記述言語：英語   出版者・発行元：Nano Letters  

We have experimentally investigated the mechanism of the exchange bias in 2D van der Waals (vdW) ferromagnets by means of the anomalous Hall effect (AHE) together with the dynamical magnetization property. The temperature dependence of the AC susceptibility with its frequency response indicates a glassy transition of the magnetic property for the Te-rich FeGeTe vdW ferromagnet. We also found that the irreversible temperature dependence in the anomalous Hall voltage follows the de Almeida-Thouless line. Moreover, the freezing temperature of the spin-glass-like phase is found to correlate with the disappearance temperature of the exchange bias. These important signatures suggest that the emergence of magnetic exchange bias in the 2D van der Waals ferromagnets is induced by the presence of the spin-glass-like state in FeGeTe. The unprecedented insights gained from these findings shed light on the underlying principles governing exchange bias in vdW ferromagnets, contributing to the advancement of our understanding.

DOI： 10.1021/acs.nanolett.4c01031

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記述言語：英語   出版者・発行元：Nature Communications  

Strongly-interacting nanomagnetic arrays are ideal systems for exploring reconfigurable magnonics. They provide huge microstate spaces and integrated solutions for storage and neuromorphic computing alongside GHz functionality. These systems may be broadly assessed by their range of reliably accessible states and the strength of magnon coupling phenomena and nonlinearities. Increasingly, nanomagnetic systems are expanding into three-dimensional architectures. This has enhanced the range of available magnetic microstates and functional behaviours, but engineering control over 3D states and dynamics remains challenging. Here, we introduce a 3D magnonic metamaterial composed from multilayered artificial spin ice nanoarrays. Comprising two magnetic layers separated by a non-magnetic spacer, each nanoisland may assume four macrospin or vortex states per magnetic layer. This creates a system with a rich 16N microstate space and intense static and dynamic dipolar magnetic coupling. The system exhibits a broad range of emergent phenomena driven by the strong inter-layer dipolar interaction, including ultrastrong magnon-magnon coupling with normalised coupling rates of Δfν=0.57, GHz mode shifts in zero applied field and chirality-control of magnetic vortex microstates with corresponding magnonic spectra.

DOI： 10.1038/s41467-024-48080-z

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Materials  

Recent discovery of 2D van der Waals magnetic materials has spurred progress in developing advanced spintronic devices. A central challenge lies in enhancing the spin-conversion efficiency for building spin-logic or spin-memory devices. Here, the anomalous Hall and Nernst effects are systematically investigated to uncover significant spin-conversion effects in above-room-temperature van der Waals ferromagnet FeGaTe with perpendicular magnetic anisotropy. The anomalous Hall effect demonstrates an efficient electric spin-charge conversion with a notable spin Hall angle of over 6%. In addition, the anomalous Nernst effect produces a significant transverse voltage at room temperature without a magnetic field, displaying unique temperature dependence with a maximum transverse Seebeck coefficient of 440 nV K−1 and a Nernst angle of ≈62%. Such an innovative thermoelectric signal arises from the efficient thermo-spin conversion effect, where the up-spin and down-spin electrons move in opposite directions under a temperature gradient. The present study highlights the potential of FeGaTe to enhance thermoelectric devices through efficient thermo-spin conversion without the need for a magnetic field.

DOI： 10.1002/adma.202309776

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Biomaterials Science and Engineering  

This study aimed to evaluate the bioactivity of poly(ether ether ketone) (PEEK) after surface modification by persistent photoconductive strontium titanate (SrTiO3) magnetron sputtering and ultraviolet (UV) C irradiation. According to the different modifications, the PEEK specimens were randomly divided into five groups (n = 38/group): PEEK, Sr100-PEEK, Sr200-PEEK, UV/PEEK, and UV/Sr200-PEEK. Then, the specimens of Sr100-PEEK and Sr200-PEEK groups were, respectively, coated with 100 and 200 nm thickness photocatalyst SrTiO3 on the PEEK surface by magnetron sputtering. Subsequently, UV-C light photofunctionalized the specimens of PEEK and Sr200-PEEK groups to form UV/PEEK and UV/Sr200-PEEK groups. The specimens were characterized by a step meter, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), and a water contact angle meter. The release test of the Sr ion was performed by inductively coupled plasma mass spectrometry (ICP-MS). In vitro study, osteogenic activity (MC3T3-E1 osteoblast-like cells) and epithelial and connective tissue attachment (gingival epithelial cells GE1 and fibroblasts NIH3T3) were analyzed in five groups. Surface morphology of the specimens was changed after coating, and the Sr content on the Sr-PEEK surface was increased with increasing coating thickness. In addition, the contact angle was increased significantly after magnetron sputtering. After UV-C photofunctionalization, the content of surface elements changed and the contact angle was decreased. The release of Sr ion was sustained, and the final cumulative release amount did not exceed the safety limit. In vitro experiments showed that SrTiO3 improved the cell activity of MC3T3-E1 and UV-C irradiation further enhanced the osteogenic performance of PEEK. Besides, UV-C irradiation also significantly promoted the cell viability, development, and expression of adhesion proteins of GE1 and NIH3T3 on PEEK. The present investigation demonstrated that nano SrTiO3 coating with UV-C photofunctionalization synergistically enhanced the osteogenic properties and soft tissue sealing function of PEEK in vitro.

DOI： 10.1021/acsbiomaterials.3c01684

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Alloys and Compounds  

Yttrium iron garnet (Y3Fe5O12, YIG) is an essential ferromagnetic insulator for enabling the transport of pure spin. The exchange coupling at the antiferromagnet/ferromagnet (AFM/FM) interface provides a means for engineering spintronic devices of YIG. In the previous results, the partially oxidized CoOx layer near the CoO/YIG interface is parallelly-coupled with the YIG layer, inducing the room temperature negative exchange bias (RT-NEB). In this study, we fabricated further oxidized CoO on YIG with sufficient O2-pressure, in which the room temperature positive exchange bias (RT-PEB) was observed. This RT-PEB can be explained if the CoO interface spins are aligned by the applied magnetic field (HAF) and coupled to YIG antiparallelly. The PEB increases with increasing HAF and saturates at HAF = 500 Oe. When the temperature is decreased below the Néel temperature of CoO, the PEB is gradually changed to NEB due to the dominance of AFM-CoO/YIG coupling. These findings pave the way for reversible modulation of the interfacial magnetic properties of insulating AFM/FM heterostructures.

DOI： 10.1016/j.jallcom.2023.172081

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

We have experimentally and theoretically investigated the influence of pressure on the spin Hall effect (SHE) for the Pt. The experimental results using a laterally configured Pt/CoFeB hybrid nanostructure suggest that the spin Hall angle for the Pt is almost constant under pressure up to 2 GPa. The theoretical study based on the first-principles calculation found the spin Hall conductivity for the Pt shows a 10% reduction due to the pressure application of 75 GPa, supporting the experimental results. These results imply that the enhanced spin Hall signal in the dynamical spin injection due to the pressure application is caused by the enhancement of the interfacial spin mixing conductance.

DOI： 10.1109/TMAG.2023.3283467

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DOI： 10.1109/TMAG.2023.3283499

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Applied  

We investigate the magnetic properties of an epitaxial full-Heusler Co2FeSi film with an atomically controlled multiferroic interface coupled with a BaTiO3 substrate. The real-space observation of the magnetic domain structure using a magneto-optical Kerr microscope reveals perfect domain-pattern transfer from the ferroelectric substrate, indicating strong interface magnetoelectric coupling. The unique anisotropic magnetization reversal process was found to be induced by lateral modulation of the magnetic anisotropy constant through the strain-induced magnetoelectric coupling effect. The strong interface coupling yields efficient electrical manipulation of the magnetic property with the appropriate initial ferroelectric domain pattern. Our finding indicates that the interface multiferroic structure based on an epitaxially grown Heusler thin film is a promising approach for efficient electrical manipulation of magnetization.

DOI： 10.1103/physrevapplied.20.034029

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevApplied.20.034029/fulltext

出版者・発行元：2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings  

We have experimentally evaluated the influence of pressure on the spin Hall effect for the Pt by using a laterally configured Pt/CoFeB hybrid nanostructure. Experimental results suggest that the spin Hall angle for the Pt is almost constant under the pressure up to 2 GPa. We have also developed the theoretical evaluation method for the pressure dependence of the spin Hall angle by using the first-principles calculation. The theoretical results also show the spin Hall angle for the Pt is insensitive to the pressure up to 75 GPa. These results imply that the enhanced spin Hall signal in the dynamical spin injection due to the pressure application is caused by the modification of the spin mixing conductance at the Pt/CoFeB interface.

DOI： 10.1109/INTERMAGShortPapers58606.2023.10228329

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings  

The magnetic voltage due to the microwave heating effect in a CoFeB/W bilayer system has been investigated experimentally. We find that the contribution from the microwave heating effect is comparable to that from the heating due to the ferromagnetic resonance at the specific field direction. We also comfirm that the magnetic signal is caused by the entanglement between anomalous Nernst and inverse spin Hall effects. This result provides an important aspect in future energy hervesting devices based on spin.

DOI： 10.1109/INTERMAGShortPapers58606.2023.10228385

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scientific Reports  

Abstract

A dynamical spin injection based on the ferromagnetic resonance in a ferromagnetic/nonmagnetic bi-layered structure, is a powerful mean for generating and manipulating the spin current. Although the mechanism of the dynamical spin injection is mainly attributed to the spin pumping, the detailed mechanism and the quantitative understanding for related phenomena are still controversial. As an another important contribution to the dynamical spin injection, the heating effect due to the resonant precessional motion of the magnetization is pointed out recently. In order to quantify the contribution from the heating effect, we here investigate the dynamical spin injection in a CoFeB/Pt/CoFeB trilayer. Although the contribution from the spin pumping diminishes because of the symmetric spin injection from the upper and lower interfaces, a significant inverse spin Hall voltage has been clearly observed. We show that the observed voltage can be quantitatively understood by the thermal spin injection due to a heating effect during the ferromagnetic resonance. A proper combination between the spin pumping and the heat-flow control in the multi-layered system is a key for the efficient dynamical spin injection.

DOI： 10.1038/s41598-022-06784-6

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その他リンク： https://www.nature.com/articles/s41598-022-06784-6

記述言語：英語   出版者・発行元：Nanomaterials  

The resonance property of a magnetic vortex contained within a micron-sized square Py dot was detected using an amplitude-modulated magnetic field excitation technique. We found a significant modulation of the resonant spectra as the external magnetic field changes. The Lorentzianlike spectrum changes from a peak to a dip via a transition of anti-Lorentzian-like spectra. By conducting the micromagnetic simulations, we confirmed that the transition behavior results from the unusual resistance change depending on the vortex core center position. Additionally, the power dependence of the anti-Lorentzian-like spectra revealed a fairly persistent coexistence of peak and dip. Thus, the tunable spectra suggest one way to develop an integratable radiofrequency microcircuits.

DOI： 10.3390/nano12132295

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出版者・発行元：Journal of Physics D: Applied Physics  

Lateral spin valves are ideal nanostructures for investigating spin-transport physics phenomena and promoting the development of future spintronic devices owing to dissipation-less pure spin current. The magnitude of the spin accumulation signal is well understood as a barometer for characterizing spin current devices. Here, we develop a novel fabrication method for lateral spin valves based on ferromagnetic nanopillar structures using a multi-angle deposition technique. We demonstrate that the spin-accumulation signal is effectively enhanced by reducing the lateral dimension of the nonmagnetic spin channel. The obtained results can be quantitatively explained by the confinement of the spin reservoir by considering spin diffusion into the leads. The temperature dependence of the spin accumulation signal and the influence of the thermal spin injection under a high bias current are also discussed.

DOI： 10.1088/1361-6463/ac47bf

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出版者・発行元：Applied Physics Express  

We experimentally investigate the influence of the pressure on the spin-charge conversion efficiency in a CoFeB/Pt bilayer system by using a specially designed pressure-cell setup. The dc voltage spectra under the dynamical spin injection is found to show the systematic increase with increasing pressure. These modifications can be understood by the enhancement of the spin-charge conversion efficiency due to the modulation of the spin-orbit interaction and/or the exchange interaction at the interface. The present demonstration indicates that the pressure provides a tunable functionality for the physical constants in spintronic devices.

DOI： 10.35848/1882-0786/ac5501

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics D: Applied Physics  

<title>Abstract</title>
A lateral spin valve consisting of highly spin-polarized CoFeAl electrodes with a CoFeAl/Cu bilayer spin channel has been developed. Despite a large spin absorption into the CoFeAl capping channel layer, an efficient spin injection and detection using the CoFeAl electrodes enable us to observe a clear spin valve signal. We demonstrate that the nonlocal spin accumulation signal is significantly modulated depending on the relative angle of the magnetizations between the spin injector and absorber. The observed modulation phenomena is explained by the longitudinal and transverse spin absorption effects into the CoFeAl channel layer with the spin resistance model.

DOI： 10.1088/1361-6463/ac34aa

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-6463/ac34aa/pdf

出版者・発行元：IEEE Transactions on Magnetics  

We have examined a dynamical spin injection in a CoFeB/Pt/CoFeB trilayered structure. Although the contribution of the spin pumping was eliminated by the symmetric spin injection from the upper and lower CoFeB layers, a clear voltage change due to the inverse spin Hall effect has been observed. We find that the observed signal can be quantitatively explained by considering the thermal spin injection due to the heating effect during ferromagnetic resonance (FMR). This innovative demonstration indicates the significant contribution of FMR heating in the dynamical spin injection.

DOI： 10.1109/TMAG.2021.3087797

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出版者・発行元：IEEE Transactions on Magnetics  

A mesoscopic multi-terminal superconducting Nb strip with a spin injection terminal has been developed. We investigate the influence of spin polarization on the relaxation process of the quasiparticle in the superconducting Nb. The position dependence of the nonlocal voltage provides the quasiparticle relaxation length. The relaxation length for the spin-polarized quasiparticle is found to show a 12.5% increase from that for the un-polarized quasiparticle. This demonstration opens a new avenue for utilization of the spin current in a superconducting device.

DOI： 10.1109/TMAG.2021.3083059

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：2D Materials  

Abstract

The magnetic exchange bias (EB) effect is one of the representative interlayer magnetic coupling phenomena and is widely utilized in numerous technological applications. However, its mechanism is still elusive even in a simple magnetic bilayered system because of the complex interface magnetic orders. Van der Waals (vdW) layered magnetic materials may provide an essential platform for deeply understanding the detailed mechanism of the EB owing to its ideal interface structure. Here we first observed the positive exchange-biased anomalous Hall effect with a hopping switching behavior in the FeGeTe vdW nano-flakes. After systemically studying the cooling field dependence properties of the EB effect, we propose that the coexistence of stable and frustrated surface magnetization of the antiferromagnetic (AFM) phase will modify the total interface coupling energy density between the ferromagnetic and AFM phases. This model could provide a consistent description for such unusual EB effect based on microspin simulation.

DOI： 10.1088/2053-1583/ac456f

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その他リンク： https://iopscience.iop.org/article/10.1088/2053-1583/ac456f/pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Status Solidi - Rapid Research Letters  

Herein, a systematic measurement of magneto-thermoelectric voltage induced in a ferromagnetic permalloy nanowire under the operation of a laterally configured nanospintronic device is performed. It is shown that the angular dependences of the magneto-thermoelectric signals with various probe configurations can be quantitatively understood by the combination of the magneto-Seebeck and anomalous Nernst effects. Surprisingly, the contribution of the transverse magneto-Seebeck effect becomes significant in a certain probe configuration, indicating the importance of the transverse heat flow. These results allow us to analyze the 3D distribution of the heat flow inside the permalloy nanowire. The present demonstration indicates that the magneto-thermoelectric effect is a powerful and reliable tool for analyzing the heat distribution in nanostructured devices.

DOI： 10.1002/pssr.202100608

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記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.35848/1882-0786/ac0b05

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0046601

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jallcom.2020.155571

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The dynamical spin injection in a ferromagnetic/paramagnetic bilayer with various paramagnetic layers has been examined by using the inverse spin Hall effect. We adapt a CoFeB film as a ferromagnetic layer, which has a large spin dependent Seebeck coefficient. The contribution of the spin pumping was evaluated from the line-width change of the ferromagnetic resonant spectra while that of the thermal spin injection was evaluated from the heat conductivity for the paramagnetic layer. We find that the spin Hall voltage does not show the systematic change with respect to the line-width change. However, the normalized spin Hall voltage is found to increase with the heat conductivity for the paramagnetic layer. These results suggest that the thermal spin injection is a major contribution for the dynamical spin injection in CoFeB/paramagnetic bilayer systems.

DOI： 10.1088/2515-7639/ab45cc

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the influence of the spin-dependent scattering on the heat transports in NiFe/Cu/NiFe and Co/Cu/Co tri-layered nanowires. The thermal conductivity and its spin dependence for the tri-layered wires have been evaluated by using an integrated nano-sized thermo couple. We find that the thermal spin-valve effect is always approximately 8 times larger than the electrical spin-valve effect, namely giant magnetoresistance effect. The numerical simulation with the experimental results enable us to estimate the thermal conductivity for the tri-layered wire and its spin dependence. Surprisingly, the spin dependence of the thermal conductivity for the Co/Cu/Co wire is as high as 8&#37;, which is much larger than the electrical one. This indicates a high potential application of the thermal spin-valve effect.

DOI： 10.1007/s10948-019-5016-5

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. We have investigated the influence of the spin-dependent scattering on the heat transports in NiFe/Cu/NiFe and Co/Cu/Co tri-layered nanowires. The thermal conductivity and its spin dependence for the tri-layered wires have been evaluated by using an integrated nano-sized thermo couple. We find that the thermal spin-valve effect is always approximately 8 times larger than the electrical spin-valve effect, namely giant magnetoresistance effect. The numerical simulation with the experimental results enable us to estimate the thermal conductivity for the tri-layered wire and its spin dependence. Surprisingly, the spin dependence of the thermal conductivity for the Co/Cu/Co wire is as high as 8&#37;, which is much larger than the electrical one. This indicates a high potential application of the thermal spin-valve effect.

DOI： 10.1007/s10948-019-5016-5

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2019 Author(s). We fabricated quasiantiferromagnetic (quasi-AFM) layers with alternating antiparallel magnetization in the neighboring domains via 90° magnetic coupling through an Fe-O layer. We investigated the magnetic properties and the relationship between the magnetic domain size and the 90° magnetic coupling via experiments and calculations. Two types of samples with a Ru buffer and a (Ni80Fe20)Cr40 buffer were prepared, and we found that with the NiFeCr buffer, the sample has a flatter Fe-O layer, leading to stronger 90° magnetic coupling and a smaller domain size compared with the Ru buffer sample. This trend is well explained by the bilinear and biquadratic coupling coefficients, A12 and B12, in Landau-Lifshitz-Gilbert simulations, suggesting the possibility of using both AFM and FM properties by controlling the quasi-AFM domain size.

DOI： 10.1063/1.5117869

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2019 We report on current-induced ferromagnetic resonance techniques to characterise spin-Hall effect at high temperatures. A microwave current was injected into a patterned CoFeB/Pt bi-layer grown on a glass substrate, simultaneously exerting spin-transfer torques through the spin-Hall effect and also causing Joule heating enabling the control of the device temperature. We measured the device temperature by using the device itself as a local temperature sensor. A clear reduction of CoFeB magnetisation was observed as the device temperature was increased allowing us to estimate the Curie temperature of our CoFeB film to be 920 K. The spin-Hall angle of Pt was quantified as (1.72 ± 0.03) × 10−2 at 300 K and was slightly increased to (1.75 ± 0.02) × 10−2 at 410 K. This simple method can be widely used for quantifying the spin-Hall angle of a large variety of materials at high temperatures.

DOI： 10.1016/j.jmmm.2019.04.070

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2019 American Physical Society. ©2019 American Physical Society. Ferromagnetic resonance (FMR) is performed on kagome artificial spin ice (ASI) formed of disconnected Ni80Fe20 nanowires. Here we break the threefold angular symmetry of the kagome lattice by altering the coercive field of each sublattice via shape anisotropy modification. This allows for distinct high-frequency responses when a magnetic field is aligned along each sublattice and additionally enables simultaneous spin-wave resonances to be excited in all nanowire sublattices, unachievable in conventional kagome ASI. The different coercive field of each sublattice allows selective magnetic switching via global field, unlocking novel microstates inaccessible in homogeneous-nanowire ASI. The distinct spin-wave spectra of these states are detected experimentally via FMR and linked to underlying microstates using micromagnetic simulation.

DOI： 10.1103/PhysRevB.100.054433

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Crystal orientation effect on spin injection/detection efficiency in Si lateral spin-valve device
We show evident crystal orientation effect on pure spin current transport in Si-based lateral spin-valve (LSV) devices with epitaxially grown CoFe/MgO tunnel contacts. When we compare nonlocal spin signals between LSV devices along < 1 0 0 > (Si < 1 0 0 >) and < 1 1 0 > (Si < 1 1 0 >), we find that the magnitude of the spin signals for Si < 100 > LSV devices is always larger than that for Si < 1 1 0 > LSV devices. The analyses based on the one-dimensional spin diffusion model reveal that the spin diffusion length and spin lifetime between Si < 1 0 0 > and Si < 1 1 0 > LSV devices are comparable, while the spin injection/detection efficiency in Si < 1 0 0 > LSV devices is evidently larger than that in Si < 1 1 0 > ones. Possible origins of the difference in the spin injection/detection efficiency between Si < 1 0 0 > and Si < 1 1 0 > LSV devices are discussed.

DOI： 10.1088/1361-6463/aaf37c

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevmaterials.2.104403

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/jjap.57.060310

記述言語：英語   掲載種別：研究論文（学術雑誌）  

An array of NiFe nanodots has been prepared on a Cu/CoFeAl film. Since a thermal spin current is expected to be excited owing to a large spin-dependent Seebeck coefficient for the CoFeAl, we investigate the magnetization dynamics of the NiFe dots under the temperature gradient along the vertical direction. By using vector network analyzer measurements, we have demonstrated that the temperature gradient produces modulations of the frequency of ferromagnetic resonance and the linewidth of the resonance spectra. The observed parabolic dependences are well explained by the damping-like and field-like components of spin transfer torque.

DOI： 10.1088/1361-6463/aabf2a

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2018 IOP Publishing Ltd. An array of NiFe nanodots has been prepared on a Cu/CoFeAl film. Since a thermal spin current is expected to be excited owing to a large spin-dependent Seebeck coefficient for the CoFeAl, we investigate the magnetization dynamics of the NiFe dots under the temperature gradient along the vertical direction. By using vector network analyzer measurements, we have demonstrated that the temperature gradient produces modulations of the frequency of ferromagnetic resonance and the linewidth of the resonance spectra. The observed parabolic dependences are well explained by the damping-like and field-like components of spin transfer torque.

DOI： 10.1088/1361-6463/aabf2a

記述言語：英語   掲載種別：研究論文（学術雑誌）  

An array of NiFe nanodots has been prepared on a Cu/CoFeAl film. Since a thermal spin current is expected to be excited owing to a large spin-dependent Seebeck coefficient for the CoFeAl, we investigate the magnetization dynamics of the NiFe dots under the temperature gradient along the vertical direction. By using vector network analyzer measurements, we have demonstrated that the temperature gradient produces modulations of the frequency of ferromagnetic resonance and the linewidth of the resonance spectra. The observed parabolic dependences are well explained by the damping-like and field-like components of spin transfer torque.

DOI： 10.1088/1361-6463/aabf2a

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1742-6596/969/1/012028

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2017 American Physical Society. Dynamical spin injection based on the ferromagnetic resonance is an attractive and powerful method for generating and manipulating the spin current. To date, in a ferromagnet/nonmagnet bilayer system, the spin-pumping effect from the ferromagnet into the nonmagnet has been considered only as the mechanism of the dynamical spin injection. Here, we examine another method for the dynamical spin injection based on the heating effect due to the ferromagnetic resonance in a (Co,Fe)B/Pt bilayer system. The (Co,Fe)B film heated by the ferromagnetic resonance produces the temperature gradient across the (Co,Fe)B/Pt interface, resulting in the thermal spin injection from the (Co,Fe)B layer into the Pt film. The obtained electrical signal clearly shows the spin Hall signature and exceeds 20 mV Ω-1 m-1, which is relatively large compared to the values reported in similar bilayer structures driven by spin pumping. The structural dependence of the inverse spin Hall signal and its power dependence provide consistent results with the dynamical thermal-spin-injection model due to the ferromagnetic resonance.

DOI： 10.1103/PhysRevApplied.8.054031

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Dynamical spin injection based on the ferromagnetic resonance is an attractive and powerful method for generating and manipulating the spin current. To date, in a ferromagnet/nonmagnet bilayer system, the spin-pumping effect from the ferromagnet into the nonmagnet has been considered only as the mechanism of the dynamical spin injection. Here, we examine another method for the dynamical spin injection based on the heating effect due to the ferromagnetic resonance in a (Co,Fe)B/Pt bilayer system. The (Co,Fe)B film heated by the ferromagnetic resonance produces the temperature gradient across the (Co,Fe)B/Pt interface, resulting in the thermal spin injection from the (Co,Fe)B layer into the Pt film. The obtained electrical signal clearly shows the spin Hall signature and exceeds 20 mV Ω-1 m-1, which is relatively large compared to the values reported in similar bilayer structures driven by spin pumping. The structural dependence of the inverse spin Hall signal and its power dependence provide consistent results with the dynamical thermal-spin-injection model due to the ferromagnetic resonance.

DOI： 10.1103/PhysRevApplied.8.054031

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Thermal spin injection is a unique and fascinating method for generating spin current. If magnetization can be controlled by thermal spin injection, various advantages will be provided in spintronic devices, through its wireless controllability. However, the generation efficiency of thermal spin injection is believed to be lower than that of electrical spin injection. Here, we explore a suitable ferromagnetic metal for an efficient thermal spin injection, via systematic experiments based on diffusive spin transport under temperature gradients. Since a ferromagnetic metal with strong spin splitting is expected to have a large spin-dependent Seebeck coefficient, a lateral spin valve based on CoFe electrodes has been fabricated. However, the superior thermal spin injection property has not been observed, because the CoFe electrode retained its crystalline signature-where s-like electrons dominate the transport property in the ferromagnet. To suppress the crystalline signature, we adopt a CoFeAl electrode, in which the Al impurity significantly reduces the contribution from s-like electrons. Highly efficient thermal spin injection has been demonstrated using this CoFeAl electrode. Further optimization for thermal spin injection has been demonstrated by adjusting the Co and Fe composition.

DOI： 10.1088/1361-6463/aa8b5b

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Thermal spin injection is a unique and fascinating method for generating spin current. If magnetization can be controlled by thermal spin injection, various advantages will be provided in spintronic devices, through its wireless controllability. However, the generation efficiency of thermal spin injection is believed to be lower than that of electrical spin injection. Here, we explore a suitable ferromagnetic metal for an efficient thermal spin injection, via systematic experiments based on diffusive spin transport under temperature gradients. Since a ferromagnetic metal with strong spin splitting is expected to have a large spin-dependent Seebeck coefficient, a lateral spin valve based on CoFe electrodes has been fabricated. However, the superior thermal spin injection property has not been observed, because the CoFe electrode retained its crystalline signature - where s-like electrons dominate the transport property in the ferromagnet. To suppress the crystalline signature, we adopt a CoFeAl electrode, in which the Al impurity significantly reduces the contribution from s-like electrons. Highly efficient thermal spin injection has been demonstrated using this CoFeAl electrode. Further optimization for thermal spin injection has been demonstrated by adjusting the Co and Fe composition.

DOI： 10.1088/1361-6463/aa8b5b

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrate that the background signal in the nonlocal spin-valve measurement can be sufficiently suppressed by optimizing the electrode design of the lateral spin valve. A relatively long length scale of heat propagation produces spin-independent thermoelectric signals under the combination of the Peltier and Seebeck effects. These unfavorable signals can be reduced by mixing the Peltier effects in two transparent ferromagnetic/nonmagnetic junctions. Proper understanding of the contribution from the heat current in no spin-current area is a key for effective reduction of the spin-independent background signal.

DOI： 10.7567/APEX.10.063004

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrate that the background signal in the nonlocal spin-valve measurement can be sufficiently suppressed by optimizing the electrode design of the lateral spin valve. A relatively long length scale of heat propagation produces spin-independent thermoelectric signals under the combination of the Peltier and Seebeck effects. These unfavorable signals can be reduced by mixing the Peltier effects in two transparent ferromagnetic/nonmagnetic junctions. Proper understanding of the contribution from the heat current in no spin-current area is a key for effective reduction of the spin-independent background signal. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/APEX.10.063004

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Electrical and thermal spin currents excited by an electric current have been systematically investigated in lateral spin valves consisting of CoFeAl and Ni80Fe20 (Py) wires bridged by a Cu strip. In the electrical spin signal, the reciprocity between the current and voltage probes was clearly confirmed. However, a significant nonreciprocity was observed in the thermal spin signal. This provides clear evidence that a large spin-dependent Seebeck coefficient is more important than the spin polarization for efficient thermal spin injection and detection. We demonstrate that the spin-dependent Seebeck coefficient can be simply evaluated from the thermal spin signals for two configurations. Our experimental description paves a way for evaluating a small spin-dependent Seebeck coefficient for conventional ferromagnets without using complicated parameters.

DOI： 10.1103/PhysRevB.95.100403

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Electrical and thermal spin currents excited by an electric current have been systematically investigated in lateral spin valves consisting of CoFeAl and Ni80Fe20 (Py) wires bridged by a Cu strip. In the electrical spin signal, the reciprocity between the current and voltage probes was clearly confirmed. However, a significant nonreciprocity was observed in the thermal spin signal. This provides clear evidence that a large spin-dependent Seebeck coefficient is more important than the spin polarization for efficient thermal spin injection and detection. We demonstrate that the spin-dependent Seebeck coefficient can be simply evaluated from the thermal spin signals for two configurations. Our experimental description paves a way for evaluating a small spin-dependent Seebeck coefficient for conventional ferromagnets without using complicated parameters.

DOI： 10.1103/PhysRevB.95.100403

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the absorption property of the diffusive pure spin current due to a ferromagnetic nanodot in a laterally configured ferromagnetic/nonmagnetic hybrid nanostructure. The spin absorption in a nano-pillar-based lateral-spin-valve structure was confirmed to increase with increasing the lateral dimension of the ferromagnetic dot. However, the absorption efficiency was smaller than that in a conventional lateral spin valve based on nanowire junctions because the large effective cross section of the two dimensional nonmagnetic film reduces the spin absorption selectivity. We also found that the absorption efficiency of the spin current is significantly enhanced by using a thick ferromagnetic nanodot. This can be understood by taking into account the spin absorption through the side surface of the ferromagnetic dot quantitatively.

DOI： 10.1063/1.4961975

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the absorption property of the diffusive pure spin current due to a ferromagnetic nanodot in a laterally configured ferromagnetic/nonmagnetic hybrid nanostructure. The spin absorption in a nano-pillar-based lateral-spin-valve structure was confirmed to increase with increasing the lateral dimension of the ferromagnetic dot. However, the absorption efficiency was smaller than that in a conventional lateral spin valve based on nanowire junctions because the large effective cross section of the two dimensional nonmagnetic film reduces the spin absorption selectivity. We also found that the absorption efficiency of the spin current is significantly enhanced by using a thick ferromagnetic nanodot. This can be understood by taking into account the spin absorption through the side surface of the ferromagnetic dot quantitatively. Published by AIP Publishing.

DOI： 10.1063/1.4961975

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

We have investigated the influence of the injection of a large pure spin current on a magnetization process of a non-locally located ferromagnetic dot in nano-pillar-based lateral spin valves. Here, we prepared two kinds of the nano-pillar-type lateral spin valve based on Py nanodots and CoFeAl nanodots fabricated on a Cu film. In the Py/Cu lateral spin valve, although any significant change of the magnetization process of the Py nanodot has not been observed at room temperature. The magnetization reversal process is found to be modified by injecting a large pure spin current at 77 K. Switching the magnetization by the nonlocal spin injection has also been demonstrated at 77 K. In the CoFeAl/Cu lateral spin valve, a room temperature spin valve signal was strongly enhanced from the Py/Cu lateral spin valve because of the highly spin-polarized CoFeAl electrodes. The room temperature nonlocal switching has been demonstrated in the CoFeAl/Cu lateral spin valve.

DOI： 10.1063/1.4961344

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the transport properties of electrically and thermally excited spin currents in a lateral spin valve consisting of a spin injector and detector with a middle ferromagnetic wire by detecting the first- and second-harmonic voltages. The first-harmonic spin signal was significantly suppressed by the middle ferromagnetic wire because of the spin absorption effect. On the other hand, in the second-harmonic signal, a small signal related to the middle ferromagnetic wire was observed in addition to a conventional spin signal with a reduced magnitude. This indicates that the additional ferromagnetic wire acts not only as the spin absorber but also as another spin injector under thermal spin injection, because the heat current caused by direct spin injection propagates to the middle ferromagnetic wire and creates another temperature gradient. By using this effect, we show that the magnetization direction of a ferromagnetic nanodot embedded in a nonmagnetic Cu wire becomes measurable.

DOI： 10.1103/PhysRevB.94.014416

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the transport properties of electrically and thermally excited spin currents in a lateral spin valve consisting of a spin injector and detector with a middle ferromagnetic wire by detecting the first- and second-harmonic voltages. The first- harmonic spin signal was significantly suppressed by the middle ferromagnetic wire because of the spin absorption effect. On the other hand, in the second-harmonic signal, a small signal related to the middle ferromagnetic wire was observed in addition to a conventional spin signal with a reduced magnitude. This indicates that the additional ferromagnetic wire acts not only as the spin absorber but also as another spin injector under thermal spin injection, because the heat current caused by direct spin injection propagates to the middle ferromagnetic wire and creates another temperature gradient. By using this effect, we show that the magnetization direction of a ferromagnetic nanodot embedded in a nonmagnetic Cu wire becomes measurable.

DOI： 10.1103/PhysRevB.94.014416

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The resonant property of the magnetic vortex confined in a square-shaped ferromagnetic dot has been investigated. We showed that the field dependence of the resonant frequency has a unique directional dependence originating from a four-fold rotational symmetry of the square. The resonant frequency is found to be strongly modulated by the magnetic field along the diagonal direction although the magnetic field applied along the side of the square hardly modified the resonant frequency. The modulation ratio of the resonant frequency defined by the ratio between minimum and maximum frequencies for the vortex resonance was found to be tuned by the lateral dimension of the square. These unique frequency tunabilities controlled by the magnitude and the direction of the magnetic field may provide additional functions in the application of the magnetic vortex systems.

DOI： 10.1016/j.physe.2015.08.038

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The resonant property of the magnetic vortex confined in a square-shaped ferromagnetic dot has been investigated. We showed that the field dependence of the resonant frequency has a unique directional dependence originating from a four-fold rotational symmetry of the square. The resonant frequency is found to be strongly modulated by the magnetic field along the diagonal direction although the magnetic field applied along the side of the square hardly modified the resonant frequency. The modulation ratio of the resonant frequency defined by the ratio between minimum and maximum frequencies for the vortex resonance was found to be tuned by the lateral dimension of the square. These unique frequency tunabilities controlled by the magnitude and the direction of the magnetic field may provide additional functions in the application of the magnetic vortex systems. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2015.08.038

記述言語：英語  

Conventional electronic devices have been based on semiconductor transistor technology, in which electron charge is controlled by electrical means. Since the emergence of the integrated circuit concept for semiconductor devices, device performance has significantly advanced via large-scale integration with the miniaturization of transistors. However, these devices are not energy efficient because of their substantial Joule heat generation and volatile characteristics. In addition, owing to recent development of top-down nanofabrication technology, device dimensions are close to the intrinsic physical scalability limits within a few-nanometer range. To overcome these serious obstacles, innovative materials, device structures, and operational principles have been recently demonstrated. In this chapter, future prospects of next-generation nanoelectronics with low power consumption are discussed with consideration of the aforementioned proposals.

DOI： 10.1007/978-4-431-55951-1_39

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have developed a fabrication process for a laterally configured resistive switching device based on a Gd oxide. A nano-gap electrode connected by a Gd oxide with the ideal interfaces has been created by adapting the electro-migration method in a metal/GdO_x bilayer system. Bipolar set and reset operations have been clearly observed in the Pt/GdO_x system similarly in the vertical device based on GdO_x. Interestingly, we were able to observe a clear bipolar switching also in a ferromagnetic CoFeB nano-gap electrode with better stability compared to the Pt/GdO_x device. The superior performance of the CoFeB/GdO_x device implies the importance of the spin on the resistive switching.

DOI： 10.1063/1.4939683

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2015 AIP Publishing LLC. We have investigated the stability for the resonant spin precession under the strong microwave magnetic field by a specially developed detection method using the anisotropic magnetoresistance effect. The electrically separated excitation and detection circuits enable us to investigate the influence of the heating effect and the nonuniform spin dynamics independently. The large detecting current is found to induce the field shift of the resonant spectra because of the Joule heating. From the microwave power dependence, we found that the linear response regime for the standing spin wave is larger than that for the ferromagnetic resonance. This robust characteristic of the standing spin wave is an important advantage for the high power operation of the spin-wave device.

DOI： 10.1063/1.4937918

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Understanding and manipulating the dynamic properties of the magnetic vortices stabilized in patterned ferromagnetic structures are of great interest owing to the superior resonant features with the high thermal stability and their flexible tunability. So far, numerous methods for investigating the dynamic properties of the magnetic vortex have been proposed and demonstrated. However, those techniques have some regulations such as spatial resolution, experimental facility and sensitivity. Here, we develop a simple and sensitive method for investigating the vortex-core dynamics by using the electrically separated excitation and detection circuits. We demonstrate that the resonant oscillation of the magnetic vortex induced by the amplitude-modulated alternating-sign magnetic field is efficiently picked up by the lock-in detection with the modulated frequency. By extending this method, we also investigate the size dependence and the influence of the magneto-static interaction in the resonant property of the magnetic vortex.

DOI： 10.1038/srep17922

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the stability for the resonant spin precession under the strong microwave magnetic field by a specially developed detection method using the anisotropic magnetoresistance effect. The electrically separated excitation and detection circuits enable us to investigate the influence of the heating effect and the nonuniform spin dynamics independently. The large detecting current is found to induce the field shift of the resonant spectra because of the Joule heating. From the microwave power dependence, we found that the linear response regime for the standing spin wave is larger than that for the ferromagnetic resonance. This robust characteristic of the standing spin wave is an important advantage for the high power operation of the spin-wave device.

DOI： 10.1063/1.4937918

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2015 AIP Publishing LLC. The heat dissipation due to the resonant precessional motion of the magnetization in a ferromagnetic metal has been investigated. We demonstrated that the temperature during the ferromagnetic resonance can be simply detected by the electrical resistance measurement of the Cu strip line in contact with the ferromagnetic metal. The temperature change of the Cu strip due to the ferromagnetic resonance was found to exceed 10 K, which significantly affects the spin-current transport. The influence of the thermal conductivity of the substrate on the heating was also investigated.

DOI： 10.1063/1.4935243

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A sensitive and reliable detection method for magnetic vortex core dynamics at the remanent state has been demonstrated. Perfectly symmetric potential created in a circular-shaped disk produces twofold symmetry in the position dependence of the resistance of the ferromagnetic disk. We find that the detectable second-harmonic voltage can be induced by flowing the dc current when the circular-shaped core oscillation is excited by the microwave magnetic field. The consistent features have been observed in the current dependence and field dependence of the signals, indicating that the present method is a powerful technique to characterize the core dynamics, even at the remanent state.

DOI： 10.1109/TMAG.2015.2435024

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The heat dissipation due to the resonant precessional motion of the magnetization in a ferromagnetic metal has been investigated. We demonstrated that the temperature during the ferromagnetic resonance can be simply detected by the electrical resistance measurement of the Cu strip line in contact with the ferromagnetic metal. The temperature change of the Cu strip due to the ferromagnetic resonance was found to exceed 10 K, which significantly affects the spin-current transport. The influence of the thermal conductivity of the substrate on the heating was also investigated.

DOI： 10.1063/1.4935243

記述言語：英語  

The transport properties of the diffusive pure spin current induced in the metallic nanostructures are discussed. The author introduces the methods for the efficient generation, manipulation, and detection of the pure spin current in laterally configured ferromagnetic/nonmagnetic metal hybrid structures. The experimental demonstration of the magnetization switching using the pure spin current is also introduced.

DOI： 10.1007/978-94-007-6892-5_55

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrate the injection and detection of electrically and thermally generated spin currents probed in Co₂MnSi/Cu lateral spin valves. Devices with different electrode separations are patterned to measure the non-local signal as a function of the electrode spacing and we determine a relatively high effective spin polarization α of Co₂MnSi to be 0.63 and the spin diffusion length of Cu to be 500 nm at room temperature. The electrically generated non-local signal is measured as a function of temperature and a maximum signal is observed for a temperature of 80 K. The thermally generated non-local signal is measured as a function of current density and temperature in a second harmonic measurement detection scheme. We find different temperature dependences for the electrically and thermally generated non-local signals, which allows us to conclude that the temperature dependence of the signals is not just dominated by the transport in the Cu wire, but there is a crucial contribution from the different generation mechanisms, which has been largely disregarded till date.

DOI： 10.1063/1.4929423

記述言語：その他   掲載種別：研究論文（その他学術会議資料等）  

© 2015 IEEE. The resonant precession of the magnetizations such as the ferromagnetic resonance (FMR) and spin wave (SW) excitation is unique and attractive property of the ferromagnetic thin film for future applications in nano-electric and telecommunication devices. Especially, after establishing the concept of the spin current, the considerable attention has been paid to such spin dynamics. Moreover, the oscillation amplitude in such resonant spin motion is found to show the nonlinear responses under the high power excitation. These fascinating properties may open novel functional spintronic devices such as spin current amplifier and neuromophic operation. However, experimental difficulties and complicated spatial spin distribution make it difficult to understand the related phenomena deeply. In this presentation, we show that nonlinear responses for the FMR and the surface SW in a Permalloy strip can be simply excited by the application of non-uniform RF magnetic field with high amplitude.

DOI： 10.1109/INTMAG.2015.7156973

記述言語：その他   掲載種別：研究論文（その他学術会議資料等）  

© 2015 IEEE. Dynamical spin injection is attractive mean for generating and controlling the spin current without the use of the electricity. So far, the mechanism of the dynamical spin injection is attributed to the spin pumping induced by the ferromagnetic resonance (FMR). Although its quantitative evaluation is not simple because of the coexistence of the dc and ac spin pumping currents, the experimental results related to the spin pumping are mainly analyzed only by focusing on the dc spin current. Since the magnitude of the ac spin current is much larger than that of the dc spin current, the consideration of the ac spin current may be important. Apart from the spin pumping, another driving mechanism for the dynamical spin injection, we are interested in the heating effect during the resonant precession. When the temperature gradient exists across the ferromagnet/ nonmagnet interface, the spin current is generated through the thermal spin injection (spin-dependent Seebeck effect)[1,2]. In this presentation, we develop the evaluation method of the FMR heating effect for the micro- or nano-sized ferromagnet and investigate the influence of the dynamical spin injection on the magnetization dynamics.

DOI： 10.1109/INTMAG.2015.7156977

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

The manipulation of spin current is a central issue in the operation of spintronic devices because the spin current plays key role both in spin-dependent transports and spin-transfer switching. Recently, a heat utilization for creating the spin current has been paid considerable attention, leading to an emerging field, spin caloritronics. One of the representative phenomena is thermal spin injection, in which excess heat can be used to produce the spin current because of the spin-dependent Seebeck coefficient [1]. However, the generation efficiency of the thermally excited spin current was quite low because of the low spin-dependent Seebeck coefficient of conventional ferromagnetic metals. The Seebeck coefficient is strongly correlated to the band structure around the Fermi level, and, under the simple approximation in metals, the coefficient is known to be proportional to the energy derivative of the logarithmic density of state (DOS) at the Fermi level. In a ferromagnetic material, since the DOS shows different features between the up and down spins, one can separately consider the moving directions of the up-spin electrons and the down-spin electrons. Therefore, in the ferromagnetic material with a large difference in the DOS between up and down spins, the sign of the Seebeck coefficient for the up-spin electron can be reversed from that for the down-spin electron. In such a situation, the up-spin and down-spin electrons flow in opposite directions, as shown in Fig. 1(a, b). Therefore, the generation efficiency of the spin current due to thermal spin injection is significantly enhanced by the large spin-dependent Seebeck coefficient.

DOI： 10.1109/INTMAG.2015.7157260

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Magnetic vortex is one of the interesting topic for the spin dynamics due to its attractive characteristic such as the high thermal stability and the small frequency dispersion. Most of studies on the magnetic vortex have been carried out by using circular-shaped ferromagnetic disk. So far, we have investigated the magnetic vortex confined in a triangular ferromagnetic dot and found some feature shown on triangular ferromagnetic dot such as the chirality of the vortex in the regular triangle can be controlled by the direction of the initialized in-plane magnetic field [1] and the resonant frequency of the vortex-core gyration motion in the triangular dot is higher than the circular one. In addition, we here report that the dynamics properties of vortex core is reconfigurable in a polygonal ferromagnetic dot due to its anisotropic shape.

DOI： 10.1109/INTMAG.2015.7156914

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Metal-insulator transition (MIT) induced by the electric field has been intensively investigated owing to its potential for nano-sized resistance switching devices in the next generation as well as its simple device structure. Although the MIT has been reported in various oxides such as Mn oxide¹⁾, Gd oxide²⁾, and Co-doped Ti oxide³⁾, the microscopic origin of the phase transition is still controversial issue. It should be noted that some of the oxides showing the MIT include magnetic components, implying that the MIT is related to the transition of the spin state. To explore the correlation between the MIT and spin configuration, in the present study, we investigate the influence of the ferromagnetic electrode on the MIT.

DOI： 10.1109/INTMAG.2015.7157166

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Resistive switching device consisting of metallic oxide layer sandwiched by the metallic electrodes has paid considerable attention to next-generation nano-electronic devices. Two major mechanisms; filament-type and interface-type, are known for the transition between the low-resistive and high-resistive states. In both mechanism, the low voltage operation is the common issue for the reliable and low-power consumption operations. From this view point, the devices, in general, consist of vertical stuck structure with the thin oxide layer. If one obtains the resistive switching operation in the laterally configured structure, we may obtain more flexible and functional device. It also should be noted that most of the metallic oxides showing the resistive switching include magnetic components^1∼3). This implies that the resistance switching is related to the spin configuration in the metallic oxide. For these purpose, in the present study, we develop a novel method for the fabrication of the switching devices in lateral configuration and investigate the influence of the ferromagnetic electrode and spin orientation on the switching property.

DOI： 10.1109/INTMAG.2015.7156918

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/srep06260

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Dynamical spin injection is attractive mean for generating and controlling the spin current without the use of the electricity. So far, the mechanism of the dynamical spin injection is attributed to the spin pumping induced by the ferromagnetic resonance (FMR). Although its quantitative evaluation is not simple because of the coexistence of the dc and ac spin pumping currents, the experimental results related to the spin pumping are mainly analyzed only by focusing on the dc spin current. Since the magnitude of the ac spin current is much larger than that of the dc spin current, the consideration of the ac spin current may be important. Apart from the spin pumping, another driving mechanism for the dynamical spin injection, we are interested in the heating effect during the resonant precession. When the temperature gradient exists across the ferromagnet/ nonmagnet interface, the spin current is generated through the thermal spin injection (spin-dependent Seebeck effect)[1,2]. In this presentation, we develop the evaluation method of the FMR heating effect for the micro- or nano-sized ferromagnet and investigate the influence of the dynamical spin injection on the magnetization dynamics.

DOI： 10.1109/INTMAG.2015.7156977

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report real-time detection of hydrogen (H) absorption in metallic palladium (Pd) nano-contacts immersed in liquid H₂ using inelastic electron spectroscopy (IES). After introduction of liquid H₂, the spectra exhibit the time evolution from the pure Pd to the Pd hydride, indicating that H atoms are absorbed in Pd nano-contacts even at the temperature where the thermal process is not expected. The IES time and bias voltage dependences show that H absorption develops by applying bias voltage 30 ∼ 50 mV, which can be explained by quantum tunneling. The results represent that IES is a powerful method to study the kinetics of high density H on solid surface.

DOI： 10.1063/1.4905729

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Efficient generation and detection of the spin current is a crucial issue for the application of spintronic devices. In addition, integrating spintronic circuit with conventional semiconductor devices is another important milestone for the practical application of the spin devices. Recently, the interplay between the heat and spin has attracted great attention because the temperature gradient is found to generate the spin current [1]. Since the heat can generate and propagate without electricity, this novel approach using the heat may open a new avenue for simplifying integration of spin devices. The precise estimation of the spin-dependent Seebeck coefficient (S_s), which is one of the important factors for the efficient generation of the thermal spin current, is indispensable to develop and optimize the spin device structure using the heat. However, it is still a hard nut to crack for the conventional ferromagnet because of its small magnitude and tiny related spin signal. Moreover, the related spin signal is smeared out by the spurious signals induced by classical thermoelectric effects especially at room temperature. Recently, we have shown that both the electrically and thermally driven spin injection efficiencies have been dramatically enhanced by the CoFeAl electrodes because of the excellent property for the thermal spin injection and electrical spin detection of CoFeAl [2]. In this presentation, by using the excellent CoFeAl, we develop the precise evaluation method for the thermal spin injection properties of Permalloy (Py)/Cu hybrid in lateral spin valve structure.

DOI： 10.1109/INTMAG.2015.7157182

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Generation of large spin current is an important issue in the operation of spintronic devices because the spin current plays a key role in spin-dependent transports and spin-transfer switching. Recently, a heat flow across a ferromagnet (FM) / nonmagnet (NM) junction is found to be able to generate and propagate the spin current. We have found that the large spin current is efficiently produced by using a heat flow across the CoFeAl /Cu junction because of the relatively large spin-dependent Seebeck coefficient for CoFeAl. The generated spin current is, in general, detected as the electrical voltage by using another ferromagnetic electrode. Using the nonlocal electrical detection scheme, one can prevent the background signal due to the spin-independent charge current. However, in the case of the thermal spin injection, the heat current reaches at the nonlocal ferromagnetic electrode and produces classical thermoelectric effects such as anomalous Nernst effect. Such spurious signals becomes serious obstacle when the large spin current is generated by the thermal spin injection. Therefore, the optimization of the device structure is indispensable for the ideal generation of the spin current using the heat. Here, we explore better geometry for generating the thermally excited spin signal in a laterally configured FM/NM hybrid nanostructure.

DOI： 10.1109/INTMAG.2015.7157183

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the dc bias current dependence of the nonlocal spin valve signal in CoFeAl/Cu lateral spin valves. The spin signal is found to increase monotonically with the bias current. Surprisingly, the modulation amplitude from -1 mA to 1 mA exceeds 30 percent of the spin signal at low bias current. From the analysis based on the one-dimensional spin diffusion model and considering the bias-current heating effect, we find that the contribution of the thermal spin injection is much larger than the influence of the reduction of the spin diffusion length due to the Joule heating. We also show that the second harmonic lock-in signal precisely extracts the contribution of the thermal spin injection from the mixed spin signal.

DOI： 10.1103/PhysRevB.90.134412

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the dc bias current dependence of the nonlocal spin valve signal in CoFeAl/Cu lateral spin valves. The spin signal is found to increase monotonically with the bias current. Surprisingly, the modulation amplitude from -1 mA to 1 mA exceeds 30 percent of the spin signal at low bias current. From the analysis based on the one-dimensional spin diffusion model and considering the bias-current heating effect, we find that the contribution of the thermal spin injection is much larger than the influence of the reduction of the spin diffusion length due to the Joule heating. We also show that the second harmonic lock-in signal precisely extracts the contribution of the thermal spin injection from the mixed spin signal.

DOI： 10.1103/PhysRevB.90.134412

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The combination between the spin-dependent and super-conducting (SC) transports is expected to provide intriguing properties such as crossed Andreev reflection and spin-triplet superconductivity. This may be able to open a new avenue in the field of spintronics, namely superconducting spintronics because a superconductor itself has great potential for future nanoelectronic applications. To observe such SC spin transports, the suppression of the extrinsic effects originating from the heating and Oersted field due to the electric current is a crucial role. Pure spin current without accompanying the charge current is known as a powerful mean for preventing such extrinsic effects. However, non-negligible heat flow is found to exist even in a conventional pure spin current device based on laterally-configured spin valve because of the heating around the spin injector. Here, we develop a nanopillar-based lateral spin valve, which significantly reduces the heat generation, on a superconducting Nb film. By using this ideal platform, we found that the spin absorption is strongly suppressed by the SC transition of Nb. This demonstration is the clear evidence that the super-conducting Nb is an insulator for the pure spin current.

DOI： 10.1038/srep06260

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Nanoelectronic devices based on electron spin can overcome the physical limitations of the present semiconductor technology because of their low power consumption while exploiting the spin degree of freedom of electrons. Although enhancing the efficiency of generation of the spin current is imperative and a primary issue for the practical application of spin-based electronics, seamless device integration with the conventional complementary metal-oxide semiconductor technology is another important milestone for developing spin-based nanoelectronics. In particular, the preparation of nanosized, magnetic, multilayered structures with electrical connections to individual complementary metal-oxide semiconductor circuits significantly complicates the fabrication procedure of nanoelectronic devices. Thermal spin injection, which is a recently discovered unique characteristic of spin current, may be an innovative method for simplifying device integration without the need for electricity, namely wireless spintronics. However, the feasibility of using the thermal spin injection method is poor because of its extremely low-generation efficiency. Here, we demonstrate that a highly spin-polarized, ferromagnetic CoFeAl electrode with a favorable band structure has excellent properties for thermal spin injection. The spin-dependent Seebeck coefficient is approximately 70 mu VK-1, which facilitates highly efficient generation of the spin current from heat. The heat generates approximately 100 times more spin voltage than a conventional ferromagnetic injector at room temperature. This innovative demonstration may open a new route for spin-device integration and its applications.

DOI： 10.1038/am.2014.74

記述言語：日本語  

7pPSA-19 Detection and nondetection of spin accumulation in multi-terminal lateral spin valve

記述言語：日本語  

10aBF-7 Indirect detection of spin signal using thermal spin injection

記述言語：日本語  

9pBF-1 Modulation of spin dynamics properties in CoFe-based ferromagnetic thin film using magnetostatic interaction

記述言語：日本語  

9pBF-2 Spin dynamics and instability of the magnetic vortex formation process of polygonal nanomagnets

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrated that the anisotropic magneto-resistance of a ferromagnetic micro-disk measured by the asymmetrically configured electrodes provide the information of the vortex chirality. The large difference of the electrical resistivity between the ferromagnetic disk and the nonmagnetic electrodes creates an inhomogeneous current distribution, allowing us to detect the local domain structure. By focusing on the chirality-dependent magneto-resistance change due to the vortex nucleation, we can clearly detect the vortex nucleation position, leading to the chirality determination. The reliability of the developed detection method has been confirmed by the magneto-resistance measurement with symmetrically configured electrodes.

DOI： 10.1063/1.4894216

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrated that the anisotropic magneto-resistance of a ferromagnetic micro-disk measured by the asymmetrically configured electrodes provide the information of the vortex chirality. The large difference of the electrical resistivity between the ferromagnetic disk and the nonmagnetic electrodes creates an inhomogeneous current distribution, allowing us to detect the local domain structure. By focusing on the chirality-dependent magneto-resistance change due to the vortex nucleation, we can clearly detect the vortex nucleation position, leading to the chirality determination. The reliability of the developed detection method has been confirmed by the magneto-resistance measurement with symmetrically configured electrodes. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4894216

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have developed a highly sensitive local magnetic sensor by using a ballistic transport property in a two-dimensional conductor. A semiclassical simulation reveals that the sensitivity increases when the geometry of the sensor and the spatial distribution of the local field are optimized. We have also experimentally demonstrated a clear observation of a magnetization process in a permalloy dot whose size is much smaller than the size of an optimized ballistic magnetic sensor fabricated from a GaAs/AlGaAs two-dimensional electron gas. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4871002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have developed a highly sensitive local magnetic sensor by using a ballistic transport property in a two-dimensional conductor. A semiclassical simulation reveals that the sensitivity increases when the geometry of the sensor and the spatial distribution of the local field are optimized. We have also experimentally demonstrated a clear observation of a magnetization process in a permalloy dot whose size is much smaller than the size of an optimized ballistic magnetic sensor fabricated from a GaAs/AlGaAs two-dimensional electron gas.

DOI： 10.1063/1.4871002

記述言語：日本語  

27aPS-7 Control of GdOx transport by spin-polarized nanogap electrodes

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Nanoelectronic devices based on electron spin can overcome the physical limitations of the present semiconductor technology because of their low power consumption while exploiting the spin degree of freedom of electrons. Although enhancing the efficiency of generation of the spin current is imperative and a primary issue for the practical application of spin-based electronics, seamless device integration with the conventional complementary metal-oxide semiconductor technology is another important milestone for developing spin-based nanoelectronics. In particular, the preparation of nanosized, magnetic, multilayered structures with electrical connections to individual complementary metal-oxide semiconductor circuits significantly complicates the fabrication procedure of nanoelectronic devices. Thermal spin injection, which is a recently discovered unique characteristic of spin current, may be an innovative method for simplifying device integration without the need for electricity, namely wireless spintronics. However, the feasibility of using the thermal spin injection method is poor because of its extremely low-generation efficiency. Here, we demonstrate that a highly spin-polarized, ferromagnetic CoFeAl electrode with a favorable band structure has excellent properties for thermal spin injection. The spin-dependent Seebeck coefficient is approximately 70 lVK^-1, which facilitates highly efficient generation of the spin current from heat. The heat generates approximately 100 times more spin voltage than a conventional ferromagnetic injector at room temperature. This innovative demonstration may open a new route for spin-device integration and its applications.

DOI： 10.1038/am.2014.74

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A magnetic vortex structure stabilized in a micron or nano-sized ferromagnetic disk has a strong potential as a unit cell for spin-based nano-electronic devices because of negligible magnetostatic interaction and superior thermal stability. Moreover, various intriguing fundamental physics such as bloch point reversal and symmetry breaking can be induced in the dynamical behaviors in the magnetic vortex. The static and dynamic properties of the magnetic vortex can be tuned by the disk dimension and/or the separation distance between the disks. However, to realize these modifications, the preparations of other devices with different sample geometries are required. Here, we experimentally demonstrate that, in a regular-triangle Permalloy dot, the dynamic properties of a magnetic vortex are greatly modified by the application of the in-plane magnetic field. The obtained wide range tunability based on the asymmetric position dependence of the core potential provides attractive performances in the microwave spintronic devices.

DOI： 10.1038/srep03567

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We show that the junction design in the laterally configured ferromagnetic/nonmagnetic (FM/NM) hybrid structure significantly affects the spin transport under high-bias current. The thermal conductivity mismatch between FM and NM and the inhomogeneous current distribution at the interface produce a reversed temperature gradient, which drastically reduces the thermal spin injection efficiency. The homogeneity in the temperature gradient at the interface is a crucial factor in determining the efficiency of the thermal spin current generation. The experimental results show excellent agreement with the theoretical model that the spin relaxation is proportional to the second spatial derivative of the temperature.

DOI： 10.1103/PhysRevB.88.184407

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We show that the difference in the Seebeck coefficients between two voltage probes produces an additional electric signal in the local resistance measurement of the submicron-sized junction. This is because the temperature increase at the junction induced by the Joule heating produces unnegligible Seebeck voltage in addition to the Ohmic voltage. In nanostructured systems, since the temperature variation becomes quite high under the high-bias current, the Seebeck voltage dominates the detected electrical voltage. This provides a consistent description for unusual bias-current dependences of the differential resistance in nano-sized metallic junction systems.

DOI： 10.1063/1.4822330

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We show that the difference in the Seebeck coefficients between two voltage probes produces an additional electric signal in the local resistance measurement of the submicron-sized junction. This is because the temperature increase at the junction induced by the Joule heating produces unnegligible Seebeck voltage in addition to the Ohmic voltage. In nanostructured systems, since the temperature variation becomes quite high under the high-bias current, the Seebeck voltage dominates the detected electrical voltage. This provides a consistent description for unusual bias-current dependences of the differential resistance in nano-sized metallic junction systems. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4822330

記述言語：日本語  

Highly efficient generation of pure spin current in nanopillar-based nonlocal spin valve.

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The ferromagnetic resonance of a single micron-scale dot of permalloy was measured by using a vector network analyzer. The resonant frequency shifted to higher frequency with increasing aspect ratio of the sample. This tendency was remarkable for narrower width samples, especially the 1-μm-width dots. This means that the demagnetization effect of thin films for the ferromagnetic resonance becomes large when the sample width is less than 1 μm. The resonant frequency can be largely controlled by changing the sample width for a thin film with a width of less than 1 μm, which is a favorable characteristics for various microwave applications. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.800

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Spin wave excitation and propagation properties in a permalloy were investigated using a vector network analyzer for the magnetostatic surface wave (MSSW) and magnetostatic backward volume wave (MSBVW) configurations. In the MSSW configuration, the excitation and transmission spectra show many peaks. They originate at the distance of antenna lines of the coplanar waveguide, and the waveguide design is important for selecting the excitation and transmission wave vectors of the spin wave. The attenuation length of the MSSW was estimated to be 7.1 μm, and the group velocity of the MSSW with a wave number of 0.26 μm-1 was estimated to be about 8.6 μm/ns for an external magnetic field of 20 mT. In the MSBVW configuration, however, the excitation spin wave spectrum shows a single peak, since many quantized peaks overlap. A transmission signal with a single peak was also detected, but this could be an artifact such as an induced current. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.083001

記述言語：日本語  

Magnetization measurement of a permalloy dot using a Hall-cross with two narrow terminals

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The ferromagnetic resonance of a single micron-scale dot of permalloy was measured by using a vector network analyzer. The resonant frequency shifted to higher frequency with increasing aspect ratio of the sample. This tendency was remarkable for narrower width samples, especially the 1-μm-width dots. This means that the demagnetization effect of thin films for the ferromagnetic resonance becomes large when the sample width is less than 1 μm. The resonant frequency can be largely controlled by changing the sample width for a thin film with a width of less than 1 μm, which is a favorable characteristics for various microwave applications.

DOI： 10.3938/jkps.63.800

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Spin wave excitation and propagation properties in a permalloy were investigated using a vector network analyzer for the magnetostatic surface wave (MSSW) and magnetostatic backward volume wave (MSBVW) configurations. In the MSSW configuration, the excitation and transmission spectra show many peaks. They originate at the distance of antenna lines of the coplanar waveguide, and the waveguide design is important for selecting the excitation and transmission wave vectors of the spin wave. The attenuation length of the MSSW was estimated to be 7.1 μm, and the group velocity of the MSSW with a wave number of 0.26 μm^-1 was estimated to be about 8.6 μm/ns for an external magnetic field of 20 mT. In the MSBVW configuration, however, the excitation spin wave spectrum shows a single peak, since many quantized peaks overlap. A transmission signal with a single peak was also detected, but this could be an artifact such as an induced current.

DOI： 10.7567/JJAP.52.083001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated a magnetization process of a permalloy nanowire by using a ballistic micro-Hall sensor consisting of GaAs/AlGaAs two-dimensional electron gas. Although a conventional bi-stable hysteresis loop with a rectangular shape was observed in the Hall resistance measurement, unexpected extra resistance changes were observed in a bend resistance measurement. These unconventional features are quantitatively explained by the magnetic transitions among the meta-stable edge-domain structures in the ferromagnetic wire. The geometrical dependence of these resistance changes and their application possibility for the multiple-valued memory were also discussed. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4812729

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated a magnetization process of a permalloy nanowire by using a ballistic micro-Hall sensor consisting of GaAs/AlGaAs two-dimensional electron gas. Although a conventional bi-stable hysteresis loop with a rectangular shape was observed in the Hall resistance measurement, unexpected extra resistance changes were observed in a bend resistance measurement. These unconventional features are quantitatively explained by the magnetic transitions among the meta-stable edge-domain structures in the ferromagnetic wire. The geometrical dependence of these resistance changes and their application possibility for the multiple-valued memory were also discussed.

DOI： 10.1063/1.4812729

記述言語：その他   掲載種別：研究論文（学術雑誌）  

We investigated the size effect on ferromagnetic resonance (FMR) in a submicron-wide single permalloy bar. The resonant frequency markedly increased with decreasing bar width to less than 1 m, since the demagnetizing field is effectively modified by changing the bar width even in thin films. The resonant frequency difference between 100- and 1000-nm-wide bars was over 4 GHz in the absence of a magnetic field. This characteristic is promising for practical microwave devices because the desired resonant frequency can be obtained simply by varying the width of narrow ferromagnetic bars so that it is not necessary to change the material or magnetic field. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.053001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Pure spin current corresponds to the flow of spin angular momentum without associating any net charge current, and possesses potential to be incorporated in special functional and high-performance devices based on nonlocal spin injection. To utilize pure spin current in practical devices, it is imperative to increase the spin generation efficiency. In this article we discuss two special configurations of nonlocal devices, known as multi-terminal injector and nanopillar devices, which possess immense potential to overcome the Joule heating problem, the key bottleneck to enhance the pure spin current generation. We also demonstrate magnetization switching of a nanosized ferromagnet due to pure spin current injection in a nanopillar-based nonlocal device.

DOI： 10.1007/s00339-012-7495-0

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Pure spin current corresponds to the flow of spin angular momentum without associating any net charge current, and possesses potential to be incorporated in special functional and high-performance devices based on nonlocal spin injection. To utilize pure spin current in practical devices, it is imperative to increase the spin generation efficiency. In this article we discuss two special configurations of nonlocal devices, known as multi-terminal injector and nanopillar devices, which possess immense potential to overcome the Joule heating problem, the key bottleneck to enhance the pure spin current generation. We also demonstrate magnetization switching of a nanosized ferromagnet due to pure spin current injection in a nanopillar-based nonlocal device.

DOI： 10.1007/s00339-012-7495-0

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigated the size effect on ferromagnetic resonance (FMR) in a submicron-wide single permalloy bar. The resonant frequency markedly increased with decreasing bar width to less than 1 m, since the demagnetizing field is effectively modified by changing the bar width even in thin films. The resonant frequency difference between 100- and 1000-nm-wide bars was over 4 GHz in the absence of a magnetic field. This characteristic is promising for practical microwave devices because the desired resonant frequency can be obtained simply by varying the width of narrow ferromagnetic bars so that it is not necessary to change the material or magnetic field.

DOI： 10.7567/JJAP.52.053001

記述言語：日本語  

27aXA-12 Distance-dependence of spin wave propagation in Py wire

記述言語：日本語  

26aPS-21 Steady-state vortex oscillation induced by spin injection and its control

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have observed unconventional asymmetric field dependence of the nonlocal spin signal under a high dc bias current injection. From the systematic studies on the bias current and the field-direction dependencies of the nonlocal signals, the origin of the asymmetry is understood as the anomalous Nernst-Ettingshausen effect driven by the bias current. The bias current dependencies of the spin accumulation signal and the background resistance are also well explained by the thermal effects induced by the bias current.

DOI： 10.1103/PhysRevB.87.014424

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have observed unconventional asymmetric field dependence of the nonlocal spin signal under a high dc bias current injection. From the systematic studies on the bias current and the field-direction dependencies of the nonlocal signals, the origin of the asymmetry is understood as the anomalous Nernst-Ettingshausen effect driven by the bias current. The bias current dependencies of the spin accumulation signal and the background resistance are also well explained by the thermal effects induced by the bias current.

DOI： 10.1103/PhysRevB.87.014424

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A magnetic resonator consisting of periodical nonmagnetic electrodes on a ferromagnetic metallic film has been fabricated. We demonstrated that the resonator efficiently excites the standing magneto-static surface spin wave with the specific wavelength, which can be controlled by the interval of the periodical electrode. The operation frequency over 5 GHz was confirmed at the interval of 4 μ m under a small bias magnetic field less than 100 Oe. The optimization of the electrode pattern for the efficient detection of the standing spin wave was also demonstrated.

DOI： 10.1063/1.4766918

記述言語：英語   掲載種別：研究論文（学術雑誌）  

So far, we have demonstrated markedly high spin polarizations (similar to 0.8) in one of the L2(1)-ordered Heusler compounds, Co2FeSi (CFS), by detecting pure spin currents using nonlocal spin-valve measurements. Here, we experimentally determine the sign of the spin polarization in the L2(1)-ordered CFS using the electrical spin Hall effect (SHE) measurements in a lateral device with Pt. Inverse SHE signals with a positive-sign hysteresis loop are clearly detected at 20 K. Since the spin Hall conductivity of Pt is the positive sign, the pure spin current generated by the CFS electrode with L2(1)-ordered structures has positive spin polarization. The SHE measurement is a powerful tool to determine the sign of the spin polarization in unknown spin injectors.

DOI： 10.1103/PhysRevB.86.174412

記述言語：英語   掲載種別：研究論文（学術雑誌）  

So far, we have demonstrated markedly high spin polarizations (∼0.8) in one of the L2 1-ordered Heusler compounds, Co 2FeSi (CFS), by detecting pure spin currents using nonlocal spin-valve measurements. Here, we experimentally determine the sign of the spin polarization in the L2 1-ordered CFS using the electrical spin Hall effect (SHE) measurements in a lateral device with Pt. Inverse SHE signals with a positive-sign hysteresis loop are clearly detected at 20 K. Since the spin Hall conductivity of Pt is the positive sign, the pure spin current generated by the CFS electrode with L2 1-ordered structures has positive spin polarization. The SHE measurement is a powerful tool to determine the sign of the spin polarization in unknown spin injectors. © 2012 American Physical Society.

DOI： 10.1103/PhysRevB.86.174412

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A magnetic resonator consisting of periodical nonmagnetic electrodes on a ferromagnetic metallic film has been fabricated. We demonstrated that the resonator efficiently excites the standing magneto-static surface spin wave with the specific wavelength, which can be controlled by the interval of the periodical electrode. The operation frequency over 5 GHz was confirmed at the interval of 4 mu m under a small bias magnetic field less than 100 Oe. The optimization of the electrode pattern for the efficient detection of the standing spin wave was also demonstrated. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4766918]

DOI： 10.1063/1.4766918

記述言語：英語   掲載種別：研究論文（学術雑誌）  

So far, we have demonstrated markedly high spin polarizations (∼0.8) in one of the L2 ₁-ordered Heusler compounds, Co ₂FeSi (CFS), by detecting pure spin currents using nonlocal spin-valve measurements. Here, we experimentally determine the sign of the spin polarization in the L2 ₁-ordered CFS using the electrical spin Hall effect (SHE) measurements in a lateral device with Pt. Inverse SHE signals with a positive-sign hysteresis loop are clearly detected at 20 K. Since the spin Hall conductivity of Pt is the positive sign, the pure spin current generated by the CFS electrode with L2 ₁-ordered structures has positive spin polarization. The SHE measurement is a powerful tool to determine the sign of the spin polarization in unknown spin injectors.

DOI： 10.1103/PhysRevB.86.174412

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Deciphering the intrinsic magnetic domain-wall (DW) resistivity of manganite materials by typical low-field magnetoresistance measurement is flawed due to the addition of different galvanomagnetic effects such as, colossal magnetoresistance, Lorentz force magnetoresistance, and anisotropic magnetoresistance (AMR). In this paper, by taking the advantage of rotational anisotropy and the stable rotation of the DW planes in half-metallic manganite La _0.7Sr _0.3MnO ₃ film, we deploy a remanent state resistance measurement technique to exclude all the field-dependent spurious effects from the intrinsic DW resistivity. To further refine its magnitude, we calculate the remanent state DW AMR by exploiting the three-dimensional micromagnetic simulation, which reveals a comparable but opposite contribution to the positive DW resistivity. From these results, we estimate the intrinsic DW resistance-area product in La _0.7Sr _0.3MnO ₃ to be 1.9×10 ^-15Ω•m2.

DOI： 10.1103/PhysRevB.86.184404

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4767341

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The static and dynamic magnetization properties in an exchange-coupled NiFe/FeMn/Cu trilayer system have been investigated. Although a clear loop shift was observed in the magnetization versus field curve, the magnitude of the exchange bias does not show a systematic dependence on the Cu thickness. On the other hand, from the ferromagnetic resonance measurements, the exchange bias is found to increase with increasing the Cu thickness. This result indicates that the resonant frequency can be controlled by the Cu thickness. The correlation between the coercivity and the damping constant is also discussed.

DOI： 10.1109/TMAG.2012.2201925

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The magnetization dynamics of a pair of the magneto-statically coupled spin torque nano oscillators (STNOs) have been investigated by using the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation with a macro-spin approximation. First, we simulated the deterministic dynamics of the coupled STNOs. Numerical simulations show that the dipole coupling mediates in-phase or out-of-phase synchronization states in the pair of the STNOs. Moreover, we found that a bistable state consisting of both in-phase and out-of phase synchronization states can exist by adjusting the experimental parameters. Second, we simulated the stochastic dynamics of the coupled STNOs under common noisy current injection. It is found that the noisy current injection into the STNOs induces to chastic state transition from the out-of-phase synchronization state to the in-phase. Such state transition arises from the cooperative effects between the noise-induced synchronization and the magneto static interactions.

DOI： 10.1109/TMAG.2012.2201145

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Spin absorption effects for the longitudinal and transverse spin currents in a Permalloy nanowire have been examined by using a lateral spin valve consisting of a V-shaped ferromagnetic injector and detector. The reduction of the nonlocal spin signal due to spin absorption for the transverse spin current was found to be stronger than that for the longitudinal spin current. This result is quantitatively explained by considering the angular dependence of the effective spin polarization, and the fact that the transverse spin relaxation length is less than half that of the longitudinal spin relaxation.

DOI： 10.1103/PhysRevB.86.104417

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Spin absorption effects for the longitudinal and transverse spin currents in a Permalloy nanowire have been examined by using a lateral spin valve consisting of a V-shaped ferromagnetic injector and detector. The reduction of the nonlocal spin signal due to spin absorption for the transverse spin current was found to be stronger than that for the longitudinal spin current. This result is quantitatively explained by considering the angular dependence of the effective spin polarization, and the fact that the transverse spin relaxation length is less than half that of the longitudinal spin relaxation.

DOI： 10.1103/PhysRevB.86.104417

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Spin absorption effects for the longitudinal and transverse spin currents in a Permalloy nanowire have been examined by using a lateral spin valve consisting of a V-shaped ferromagnetic injector and detector. The reduction of the nonlocal spin signal due to spin absorption for the transverse spin current was found to be stronger than that for the longitudinal spin current. This result is quantitatively explained by considering the angular dependence of the effective spin polarization, and the fact that the transverse spin relaxation length is less than half that of the longitudinal spin relaxation. © 2012 American Physical Society.

DOI： 10.1103/PhysRevB.86.104417

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We measured the magnetoresistance (MR) of Pd nanometer-scale constrictions while changing the constriction size by stretching the Pd wire using a mechanically controllable break junction technique. In large constrictions, the resistance is constant for | H | 400 Oe, reflecting bulk Pd paramagnetic properties. As size decreases to ∼10 nm, the MR effect with hysteresis is observed with a sweeping field, indicating the ferromagnetic transition in Pd constrictions. We proposed this technique to detect ferromagnetic transitions caused by downsizing in paramagnetic metals and to study magnetic properties after the transitions.

DOI： 10.1063/1.4754565

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We study the electrical conductance in a ferromagnetic Ni constriction, changing its size using a mechanically controllable break junction technique. A Fano resonance with a zero-bias anomaly, likely due to the Kondo effect, appears in Ni atomic-scale contacts and changes shape as the size of the contact changes. Moreover, the zero-bias anomaly persists in large size constrictions with nearly 50-atom configurations where the bulk ferromagnetic properties should be retained, despite the decrease of the signal intensity. The results suggest that the Kondo effect and ferromagnetism could coexist in the ferromagnetic nanoconstrictions.

DOI： 10.1103/PhysRevB.86.064404

記述言語：日本語  

18pPSA-16 Magnetization dynamics induced by pure spin current

記述言語：英語   掲載種別：研究論文（学術雑誌）  

An advantageous device structure for the efficient electrical detection of spin Hall effect has been demonstrated by using a V-shaped ferromagnetic wire. The spin Hall voltages were evaluated by the combination between the spin absorption into the Platinum strip and the desired spin structure in the V-shaped Permalloy wire. Rectangular-shape field dependence of the spin Hall signal with bistability in the zero magnetic field reveals the validity of the developed device structure. We also showed that the domain wall chirality trapped at the corner of the V-shape wire can be determined from the sign of the spin Hall voltage.

DOI： 10.1063/1.4747219

記述言語：英語   掲載種別：研究論文（学術雑誌）  

An advantageous device structure for the efficient electrical detection of spin Hall effect has been demonstrated by using a V-shaped ferromagnetic wire. The spin Hall voltages were evaluated by the combination between the spin absorption into the Platinum strip and the desired spin structure in the V-shaped Permalloy wire. Rectangular-shape field dependence of the spin Hall signal with bistability in the zero magnetic field reveals the validity of the developed device structure. We also showed that the domain wall chirality trapped at the corner of the V-shape wire can be determined from the sign of the spin Hall voltage. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4747219]

DOI： 10.1063/1.4747219

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We study the electrical conductance in a ferromagnetic Ni constriction, changing its size using a mechanically controllable break junction technique. A Fano resonance with a zero-bias anomaly, likely due to the Kondo effect, appears in Ni atomic-scale contacts and changes shape as the size of the contact changes. Moreover, the zero-bias anomaly persists in large size constrictions with nearly 50-atom configurations where the bulk ferromagnetic properties should be retained, despite the decrease of the signal intensity. The results suggest that the Kondo effect and ferromagnetism could coexist in the ferromagnetic nanoconstrictions.

DOI： 10.1103/PhysRevB.86.064404

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have proposed a novel device geometry of the bend resistance for collimated ballistic electrons with high magnetic sensitivity. The field response of the bend resistance can be effectively tuned by changing the relative position between two point contacts. The asymmetric field dependence of the bend resistance is found to be induced by introducing conductance asymmetry between the two point contacts. The validity of the proposed device was also confirmed experimentally by using a patterned GaAs/AlGaAs two-dimensional electron gas system. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/APEX.5.073001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have proposed a novel device geometry of the bend resistance for collimated ballistic electrons with high magnetic sensitivity. The field response of the bend resistance can be effectively tuned by changing the relative position between two point contacts. The asymmetric field dependence of the bend resistance is found to be induced by introducing conductance asymmetry between the two point contacts. The validity of the proposed device was also confirmed experimentally by using a patterned GaAs/AlGaAs two-dimensional electron gas system.

DOI： 10.1143/APEX.5.073001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Using single-crystalline spin injectors and detectors, we examine the effect of the addition of Al to CoFe electrodes on nonlocal spin signals in metallic lateral spin valves (LSVs). A molecular beam epitaxy technique enables us to obtain Heusler-alloy-like CoFeAl epitaxial layers with an ordered B2 structure. The LSVs with the CoFeAl electrodes show a remarkable enhancement of the nonlocal spin signals, six times larger than that of the LSV with the CoFe electrodes, at room temperature. The relatively low electrical resistivity of the CoFeAl electrodes means that the enhancement of the spin signals originates from an increase in the spin polarization due to the Al addition to CoFe.

DOI： 10.1143/APEX.5.063004

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Using single-crystalline spin injectors and detectors, we examine the effect of the addition of Al to CoFe electrodes on nonlocal spin signals in metallic lateral spin valves (LSVs). A molecular beam epitaxy technique enables us to obtain Heusler-alloy-like CoFeAl epitaxial layers with an ordered B2 structure. The LSVs with the CoFeAl electrodes show a remarkable enhancement of the nonlocal spin signals, six times larger than that of the LSV with the CoFe electrodes, at room temperature. The relatively low electrical resistivity of the CoFeAl electrodes means that the enhancement of the spin signals originates from an increase in the spin polarization due to the Al addition to CoFe. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/APEX.5.063004

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Two advantages of the lateral spin valve using multi-terminal spin injections have been demonstrated. First, the effective spin polarization for the pure spin current can be controlled by the two anti-parallely aligned spin injectors. We show that the magnitude and the sign of the spin polarization are electrically manipulated by adjusting the current ratio between two injectors. Secondly, we show that the giant pure spin current can be generated by the nonlolcal spin injections from the quadruple spin injectors.

DOI： 10.1063/1.3672245

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have numerically studied the stochastic magnetization dynamics of a pair of spin torque nano oscillators (STNOs) under noisy current injection by using the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation with a macro-spin approximation. Common noisy current injection into both STNOs is found to induce the phase synchronizations, where two STNOs show in-phase or anti-phase locked precession depending on the sequences of Gaussian white noise. The noise-induced synchronization could be a possible application for controlling the output power in the array of the STNOs. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3680537]

DOI： 10.1063/1.3680537

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have studied the magnetic domain structures in a magneto-statically-coupled chain array of the triangle dots and an isosceles triangle dot by means of magnetic force microscopy (MFM). Despite the strong magneto-static interaction in the chain array of the dots, each triangle dot takes a single vortex structure. The chirality of each dot is found to behave similarly to that for the isolated triangle dot. We also demonstrated that single-vortex and double-vortex structures with the desired chiralities can be stabilized in an isosceles triangle dot. (C) 2012 American Institute of Physics. [doi:10.1063/1.3673349]

DOI： 10.1063/1.3673349

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Two advantages of the lateral spin valve using multi-terminal spin injections have been demonstrated. First, the effective spin polarization for the pure spin current can be controlled by the two anti-parallely aligned spin injectors. We show that the magnitude and the sign of the spin polarization are electrically manipulated by adjusting the current ratio between two injectors. Secondly, we show that the giant pure spin current can be generated by the nonlolcal spin injections from the quadruple spin injectors. (C) 2012 American Institute of Physics. [doi:10.1063/1.3672245]

DOI： 10.1063/1.3672245

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The time evolution of vortex spin structures in ferromagnetic FeNi disks (4 μm and 6 μm in diameter and thickness of 30 nm) during fast magnetic field pulses was observed by time-resolved x-ray magnetic circular dichroism with photoelectron emission microscopy. For the smaller disk, the displacement of the vortex core was found to linearly follow the field amplitude as described by an analytical model based on Thiele's equation with boundary conditions for patterned magnets. In contrast, for the larger disk which contains a smaller magnetic restoring force, a nonlinear response of the core displacement to the field amplitude, and also a sub-ns delay of the core motion, was observed. In parallel a deformation of the vortex spin structure was observed. Part of the Zeeman energy is stored in deforming the vortex structure during the rise time of the magnetic field with a large ΔH/Δt.

DOI： 10.1103/PhysRevB.85.134414

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have numerically studied the stochastic magnetization dynamics of a pair of spin torque nano oscillators (STNOs) under noisy current injection by using the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation with a macro-spin approximation. Common noisy current injection into both STNOs is found to induce the phase synchronizations, where two STNOs show in-phase or anti-phase locked precession depending on the sequences of Gaussian white noise. The noise-induced synchronization could be a possible application for controlling the output power in the array of the STNOs.

DOI： 10.1063/1.3680537

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have studied the magnetic domain structures in a magneto-statically- coupled chain array of the triangle dots and an isosceles triangle dot by means of magnetic force microscopy (MFM). Despite the strong magneto-static interaction in the chain array of the dots, each triangle dot takes a single vortex structure. The chirality of each dot is found to behave similarly to that for the isolated triangle dot. We also demonstrated that single-vortex and double-vortex structures with the desired chiralities can be stabilized in an isosceles triangle dot.

DOI： 10.1063/1.3673349

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We study room-temperature generation and detection of pure spin currents using lateral spin-valve devices with electrodes formed from the Heusler compounds Co 2FeSi (CFS) or Fe 3Si (FS). The magnitude of the nonlocal spin-valve signals is strongly affected by resistivity variations observed particularly in low-temperature-grown Heusler compounds containing ordered structures. From an analysis based on a one-dimensional spin diffusion model, we find that the spin polarization monotonically increases with decreasing resistivity, which depends on the structural ordering, for both the CFS and FS electrodes, and show that CFS has a larger spin polarization than FS. © 2012 American Physical Society.

DOI： 10.1103/PhysRevB.85.100404

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We study room-temperature generation and detection of pure spin currents using lateral spin-valve devices with electrodes formed from the Heusler compounds Co ₂FeSi (CFS) or Fe ₃Si (FS). The magnitude of the nonlocal spin-valve signals is strongly affected by resistivity variations observed particularly in low-temperature-grown Heusler compounds containing ordered structures. From an analysis based on a one-dimensional spin diffusion model, we find that the spin polarization monotonically increases with decreasing resistivity, which depends on the structural ordering, for both the CFS and FS electrodes, and show that CFS has a larger spin polarization than FS.

DOI： 10.1103/PhysRevB.85.100404

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The generation, manipulation and detection of a pure spin current (i.e., the flow of spin angular momentum without a charge current) are prospective approaches for realizing next-generation spintronic devices with ultra-low electric power consumption. Conventional ferromagnetic electrodes such as Co and NiFe have been utilized as spin injectors to generate pure spin currents in nonmagnetic channels. However, the generation efficiency of pure spin currents is extremely low at room temperature, giving rise to a serious obstacle for device applications. Here we demonstrate the generation of giant pure spin currents at room temperature in lateral spin valve devices with a highly ordered Heusler-compound Co2FeSi (CFS) spin injector. The generation efficiency of pure spin currents from the CFS spin injectors is 10 times greater than that of the NiFe injectors, indicating that Heusler compound spin injectors with high spin polarization enable us to materialize a high-performance lateral spin device. The present study is a technological jump in spintronics, and indicates the great potential of ferromagnetic Heusler compounds with half metallicity for generating pure spin currents. NPG Asia Materials (2012) 0, e9; doi:10.1038/am.2012.16; published online 9 March 2012

DOI： 10.1038/am.2012.16

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A different type lateral spin valve structure consisting of a pair of the closely located Permalloy nanopillars on a uniform copper film has been developed. From the bias-current and temperature dependences of the spin signal, the nanopillar lateral spin valve was found to have several advantages for generating the pure spin current over the conventional lateral spin valves. We also show that the limitation of the generating spin current can be enhanced by increasing the number of the spin injectors. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3698092]

DOI： 10.1063/1.3698092

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We study room-temperature generation and detection of pure spin currents using lateral spin-valve devices with electrodes formed from the Heusler compounds Co2FeSi (CFS) or Fe3Si (FS). The magnitude of the nonlocal spin-valve signals is strongly affected by resistivity variations observed particularly in low-temperature-grown Heusler compounds containing ordered structures. From an analysis based on a one-dimensional spin diffusion model, we find that the spin polarization monotonically increases with decreasing resistivity, which depends on the structural ordering, for both the CFS and FS electrodes, and show that CFS has a larger spin polarization than FS.

DOI： 10.1103/PhysRevB.85.100404

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A different type lateral spin valve structure consisting of a pair of the closely located Permalloy nanopillars on a uniform copper film has been developed. From the bias-current and temperature dependences of the spin signal, the nanopillar lateral spin valve was found to have several advantages for generating the pure spin current over the conventional lateral spin valves. We also show that the limitation of the generating spin current can be enhanced by increasing the number of the spin injectors.

DOI： 10.1063/1.3698092

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The generation, manipulation and detection of a pure spin current (i.e., the flow of spin angular momentum without a charge current) are prospective approaches for realizing next-generation spintronic devices with ultra-low electric power consumption. Conventional ferromagnetic electrodes such as Co and NiFe have been utilized as spin injectors to generate pure spin currents in nonmagnetic channels. However, the generation efficiency of pure spin currents is extremely low at room temperature, giving rise to a serious obstacle for device applications. Here we demonstrate the generation of giant pure spin currents at room temperature in lateral spin valve devices with a highly ordered Heusler-compound Co₂FeSi (CFS) spin injector. The generation efficiency of pure spin currents from the CFS spin injectors is 10 times greater than that of the NiFe injectors, indicating that Heusler compound spin injectors with high spin polarization enable us to materialize a high-performance lateral spin device. The present study is a technological jump in spintronics, and indicates the great potential of ferromagnetic Heusler compounds with half metallicity for generating pure spin currents.

DOI： 10.1038/am.2012.16

記述言語：英語  

We have proposed a method for controlling the vortex chirality in a squared permalloy dot by using the circular Oersted field locally induced by flowing a DC current across a small Py/Cu junctions. The reliability of the chirality control has been evaluated by measuring the nonlocal spin valve signal. The desired vortex chirality has been obtained when the injecting DC current has a moderate magnitude. However, the large DC current is found to reduce the control reliability. Another possibility for controlling the vortex structure using the large DC current injection was also discussed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3669410]

DOI： 10.1063/1.3669410

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have proposed a method for controlling the vortex chirality in a squared permalloy dot by using the circular Oersted field locally induced by flowing a DC current across a small Py/Cu junctions. The reliability of the chirality control has been evaluated by measuring the nonlocal spin valve signal. The desired vortex chirality has been obtained when the injecting DC current has a moderate magnitude. However, the large DC current is found to reduce the control reliability. Another possibility for controlling the vortex structure using the large DC current injection was also discussed.

DOI： 10.1063/1.3669410

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Static and dynamical properties of a magnetic vortex stabilized in a regular polygonal nanomagnet were investigated. We have demonstrated that the chirality of the magnetic vortex in a odd-sided regular nanomagnet can be controlled by the in-plane magnetic field. We also observed the resonant spectrum of a vortex core in the triangular nanomagnet using the homodyne detection technique. The resonant frequency of the vortex core in the triangular nanomagnet was found to be higher than that in a circular nanomagnet.

DOI： 10.1109/TMAG.2011.2158408

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the magneto- and spin-current-transport properties in patterned Gd wires in order to understand the interplay between the spin current and the spin entropy. From the magneto-transport measurements, the electrical resistance was found to decrease with decreasing the spin entropy because of the suppression of the spin fluctuation. We also found that the Gd acts as a strong absorber both for the ac and dc pure spin currents from the ferromagnetic resonance and nonlocal spin injection experiments.

DOI： 10.1109/TMAG.2011.2158407

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Static and dynamical properties of a magnetic vortex stabilized in a regular polygonal nanomagnet were investigated. We have demonstrated that the chirality of the magnetic vortex in a odd-sided regular nanomagnet can be controlled by the in-plane magnetic field. We also observed the resonant spectrum of a vortex core in the triangular nanomagnet using the homodyne detection technique. The resonant frequency of the vortex core in the triangular nanomagnet was found to be higher than that in a circular nanomagnet.

DOI： 10.1109/TMAG.2011.2158408

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the magneto- and spin-current-transport properties in patterned Gd wires in order to understand the interplay between the spin current and the spin entropy. From the magneto-transport measurements, the electrical resistance was found to decrease with decreasing the spin entropy because of the suppression of the spin fluctuation. We also found that the Gd acts as a strong absorber both for the ac and dc pure spin currents from the ferromagnetic resonance and nonlocal spin injection experiments.

DOI： 10.1109/TMAG.2011.2158407

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The transport properties of diffusive spin currents have been investigated in lateral ferromagnetic/non-magnetic metal hybrid structures. The spin diffusion processes were found to be strongly dependent on the magnitude of the spin resistances of connected materials. Efficient spin injection and detection are accomplished by optimizing the junction structures on the basis of the spin resistance circuitry. The magnetization switching of a nanoscale ferromagnetic particle and also room temperature spin Hall effect measurements were realized by using an efficient pure-spin-current injection.

DOI： 10.1098/rsta.2011.0010

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report on the fabrication of metallic lateral spin valves using different evaporation directions for respective ferromagnetic and nonmagnetic materials. In this way, we can fabricate and connect different nanowires through the same resist mask in a single evaporation sequence, avoiding interface contamination. With this technique and by reducing the wire widths down to 50 nm, we obtained spin signals as large as 24mω at 77 K in devices with transparent interfaces. We studied the influence of the nonmagnetic metal. Spin signals are found to be much larger for Al and Cu than for Au-based devices.

DOI： 10.1143/APEX.4.063007

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We here experimentally demonstrate that gyration modes of coupled vortices can be resonantly excited primarily by the ac current in a pair of ferromagnetic disks with variable separation. The sole gyration mode clearly splits into higher and lower frequency modes via dipolar interaction, where the main mode splitting is due to a chirality sensitive phase difference in gyrations of the coupled vortices, whereas the magnitude of the splitting is determined by their polarity configuration. These experimental results show that the coupled pair of vortices behaves similar to a diatomic molecule with bonding and antibonding states, implying a possibility for designing the magnonic band structure in a chain or an array of magnetic vortex oscillators.

DOI： 10.1103/PhysRevLett.106.197203

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated spin Hall effects in 4d and 5d transition metals, Nb, Ta, Mo, Pd, and Pt, by incorporating the spin absorption method in the lateral spin valve structure, where large spin current preferably relaxes into the transition metals, exhibiting strong spin-orbit interactions. Thereby nonlocal spin valve measurements enable us to evaluate their spin Hall conductivities. The sign of the spin Hall conductivity changes systematically depending on the number of d electrons. This tendency is in good agreement with the recent theoretical calculation based on the intrinsic spin Hall effect.

DOI： 10.1103/PhysRevB.83.174405

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated spin Hall effects in 4d and 5d transition metals, Nb, Ta, Mo, Pd, and Pt, by incorporating the spin absorption method in the lateral spin valve structure, where large spin current preferably relaxes into the transition metals, exhibiting strong spin-orbit interactions. Thereby nonlocal spin valve measurements enable us to evaluate their spin Hall conductivities. The sign of the spin Hall conductivity changes systematically depending on the number of d electrons. This tendency is in good agreement with the recent theoretical calculation based on the intrinsic spin Hall effect.

DOI： 10.1103/PhysRevB.83.174405

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The dynamics of magnetostatically coupled vortices in a pair of ferromagnetic micron-sized disks has been observed in real space by pump-probe time-resolved photoemission electron microscopy. It is found that the dynamics of paired vortices is affected by a magnetic dipolar interaction. The displacement of a vortex core from its equilibrium position in the paired vortices during the supply of a magnetic field pulse is smaller than that in the isolated vortex, which is in qualitative agreement with micromagnetic simulation results. Unexpectedly, two eigenfrequencies of the paired vortices are different from each other. When the separation distance between the paired disks is shorter, the difference between the two eigenfrequencies is larger.

DOI： 10.1143/JJAP.50.053001

記述言語：日本語  

26aPS-30 Detection of loop current induced by pure spin current

記述言語：日本語  

26aPS-33 Electrical detection of pure spin current using a quaternary Heusler-compound spin injector and detector

記述言語：日本語  

26aPS-34 Electrical detection of spin Hall effect in lateral spin-valve devices with Heusler-compound electrodes

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We microscopically investigate the magnetic domain wall motion induced by current pulse application in a small in-plane magnetic field in U-shaped Permalloy wires by means of Lorentz microscopy together with simultaneous transport measurement. An in-plane magnetic field less than 7 Oe parallel to the wire direction in U-shaped geometry effectively works to impede bidirectional motion of the domain wall induced by current pulse application, i.e. to suppress the stochastic nature of the domain wall displacement. The present finding will provide practical and reliable ways of controlling and manipulating the domain wall dynamics, which are widely applicable in spintronic devices, especially when stochastic nature causes serious problems in device operation. Reliable manipulation of the magnetic state is discussed using the current-driven domain wall motion and domain nucleation in the magnetic wire device.

DOI： 10.1088/0022-3727/44/6/064015

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We microscopically investigate the magnetic domain wall motion induced by current pulse application in a small in-plane magnetic field in U-shaped Permalloy wires by means of Lorentz microscopy together with simultaneous transport measurement. An in-plane magnetic field less than 7 Oe parallel to the wire direction in U-shaped geometry effectively works to impede bidirectional motion of the domain wall induced by current pulse application, i.e. to suppress the stochastic nature of the domain wall displacement. The present finding will provide practical and reliable ways of controlling and manipulating the domain wall dynamics, which are widely applicable in spintronic devices, especially when stochastic nature causes serious problems in device operation. Reliable manipulation of the magnetic state is discussed using the current-driven domain wall motion and domain nucleation in the magnetic wire device.

DOI： 10.1088/0022-3727/44/6/064015

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have fabricated multi-terminal superconductor/normal metal/superconductor junctions comprising superconductor Nb and normal metal Cu. By means of the local and non-local measurements of the junction, we successfully detected the non-existence of a bias current in the Cu wire and the non-local voltage. These results indicate that the current flowing non-locally over the junction is due to the proximity effects and the conversion of the supercurrent and normal current.

DOI： 10.1007/s10948-010-0992-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The transport properties of diffusive spin currents have been investigated in lateral ferromagnetic/nonmagnetic metal hybrid structures. The spin diffusion processes were found strongly dependent on the magnitude of the spin resistances of connected materials. The efficient spin injection and detection are accomplished by optimizing the junction structures on the basis of the spin resistance circuitry. The magnetization switching of a nano-scale ferromagnetic particle and also room temperature spin Hall effect measurements were demonstrated by using an efficient pure-spin-current injection. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2010.07.041

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have fabricated multi-terminal superconductor/normal metal/superconductor junctions comprising superconductor Nb and normal metal Cu. By means of the local and non-local measurements of the junction, we successfully detected the non-existence of a bias current in the Cu wire and the non-local voltage. These results indicate that the current flowing non-locally over the junction is due to the proximity effects and the conversion of the supercurrent and normal current.

DOI： 10.1007/s10948-010-0992-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The transport properties of diffusive spin currents have been investigated in lateral ferromagnetic/nonmagnetic metal hybrid structures. The spin diffusion processes were found strongly dependent on the magnitude of the spin resistances of connected materials. The efficient spin injection and detection are accomplished by optimizing the junction structures on the basis of the spin resistance circuitry. The magnetization switching of a nano-scale ferromagnetic particle and also room temperature spin Hall effect measurements were demonstrated by using an efficient pure-spin-current injection.

DOI： 10.1016/j.physe.2010.07.041

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The authors propose a nonvolatile multiple-valued memory based on a nonlocal spin valve structure. Multibit informations are formed by changing the magnetization configuration in a nonlocal voltage probe consisting of a magnetic multilayer. A simple calculation method for the spin-accumulation voltage induced in lateral ferromagnetic/nonmagnetic multilayered hybrid structures is also developed on the basis of the spin resistance model. The developed model enables us to find the thickness of each ferromagnetic layer for the optimized operation of the multiple-valued memory. (c) 2010 American Institute of Physics. [doi:10.1063/1.3502475]

DOI： 10.1063/1.3502475

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The authors propose a nonvolatile multiple-valued memory based on a nonlocal spin valve structure. Multibit informations are formed by changing the magnetization configuration in a nonlocal voltage probe consisting of a magnetic multilayer. A simple calculation method for the spin-accumulation voltage induced in lateral ferromagnetic/nonmagnetic multilayered hybrid structures is also developed on the basis of the spin resistance model. The developed model enables us to find the thickness of each ferromagnetic layer for the optimized operation of the multiple-valued memory.

DOI： 10.1063/1.3502475

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The authors have proposed a control method of the magnetic vortex chirality in regular polygonal nanomagnets with an odd number of sides. The asymmetric nucleation energy of the vortex from the uniformly magnetized state enables us to simply control the vortex chirality by an in-plane magnetic field. The reliability of the proposed method has been numerically and experimentally confirmed in the triangle, pentagonal, heptagonal, and nonagonal Permalloy nanomagnets. The authors also confirmed that the vortex chirality is uncontrollable when the number of the side is even.

DOI： 10.1063/1.3521407

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We present the experimental observation of gyration mode splitting by the time-resolved magneto-optical Kerr effect in an array consisting of magnetostatically coupled Ni81Fe19 discs of 1 μm diameter, 50 nm thickness and inter-disc separations varying between 150 and 270 nm. A splitting of the vortex core gyration mode is observed when the inter-disc separation is 200 nm or less and the splitting is controllable by a bias magnetic field. The observed mode splitting is interpreted by micromagnetic simulations as the normal modes of the vortex cores analogous to the coupled classical oscillators. The splitting depends upon the strength of the inter-disc magnetostatic coupling mediated by magnetic side charges, which depends strongly on the magnetic ground states of the samples.

DOI： 10.1088/0022-3727/43/42/422001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We perform a detailed comparison of the nonlocal magnetoresistance (MR) curve with the local MR ones in Si-based lateral spin-valve devices with epitaxial ferromagnetic Fe₃Si contacts, where the local MR originates from the anisotropic MR of the ferromagnetic contacts. We find that the nonlocal MR signals clearly depend on the magnetization reversal of the contacts, and they show positive or negative peak values when the magnetic configuration between two ferromagnetic contacts becomes nearly anti-parallel. These features mean that the obtained nonlocal MR signals can be distinguished from the suspicious signals, indicating a reliable result of the spin transport in Si.

DOI： 10.1143/APEX.3.093001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Pure spin current injection into a superconductive Nb was demonstrated experimentally by employing a nonlocal spin absorption technique in a multiterminal lateral structure. From the reduction in spin signals, we found the absorption efficiency remained almost unchanged even after superconducting transition. The Nb/Cu interface properties were also complementarily examined by using a Nb/Cu/Nb junction incorporated in the same device, revealing superconductivity below the transition temperature. These experimental results support that the pure spin current can be absorbed into a superconductive Nb wire with almost the same efficiency as in a normal state.

DOI： 10.1063/1.3427483

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In the third- and coming fourth-generation synchrotron radiation facilities, X-rays having both high brightness and high coherency can be utilized. Such X-rays require high accuracy in the reflective optics. In this study, we developed an ultra-precise measurement instrumentation for tangentially long X-ray mirrors using a Fizeau interferometer. In the system, the mirror figure is measured by stitching the subaperture profiles measured by the relative-angle determinable stitching interferometry, which we developed previously. High measurement accuracy of approximately 2 nm (peak to valley) was achieved in the measurement of a 400 mm-long aspherical surface.

DOI： 10.1016/j.nima.2009.11.014

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Pure spin current injection into a superconductive Nb was demonstrated experimentally by employing a nonlocal spin absorption technique in a multiterminal lateral structure. From the reduction in spin signals, we found the absorption efficiency remained almost unchanged even after superconducting transition. The Nb/Cu interface properties were also complementarily examined by using a Nb/Cu/Nb junction incorporated in the same device, revealing superconductivity below the transition temperature. These experimental results support that the pure spin current can be absorbed into a superconductive Nb wire with almost the same efficiency as in a normal state. (C) 2010 American Institute of Physics. [doi:10.1063/1.3427483]

DOI： 10.1063/1.3427483

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate crystalline structures of a permalloy nanowire subject to current pulses by using standard transmission and scanning electron microscope techniques, together with the analysis of magnetic states by means of Lorenz microscopy. We find that crystalline grains grow slightly larger in a current region around the Curie temperature, which does not affect significantly the uniformly-magnetized state in the wire because of strong uniaxial shape anisotropy given by the wire geometry. When crystalline grains grow large enough to additionally provide in-plane anisotropy comparable to the shape anisotropy by averaging crystalline anisotropy over the grains, the magnetic ripple will be induced in the wire. Such situations can be found in the case when very large current pulses are applied to the wire. (C) 2010 American Institute of Physics. [doi:10.1063/1.3356229]

DOI： 10.1063/1.3356229

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate crystalline structures of a permalloy nanowire subject to current pulses by using standard transmission and scanning electron microscope techniques, together with the analysis of magnetic states by means of Lorenz microscopy. We find that crystalline grains grow slightly larger in a current region around the Curie temperature, which does not affect significantly the uniformly-magnetized state in the wire because of strong uniaxial shape anisotropy given by the wire geometry. When crystalline grains grow large enough to additionally provide in-plane anisotropy comparable to the shape anisotropy by averaging crystalline anisotropy over the grains, the magnetic ripple will be induced in the wire. Such situations can be found in the case when very large current pulses are applied to the wire.

DOI： 10.1063/1.3356229

記述言語：日本語  

22pGJ-2 Extrinsic Spin Hall Effect in CuIr wire II

記述言語：日本語  

20aPS-18 Hanle effect in lateral spin valves consisting of ohmic and tunnel junctions

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

We have proposed a method for controlling the vortex chirality in a regular polygonal nanomagnet with an odd number of sides using an in-plane magnetic field. We confirmed the reliability of the proposed method in the triangle, pentagonal and heptagonal nanomagnets by using micromagnetic simulation. However, when the number of the sides is 9 or more, the chirality does not change systematically because of the insufficient in-plane shape anisotropy. Stabilizations of a single vortex in polygonal nanomagnets with an even number of sides have been also investigated.

DOI： 10.1109/TENCON.2010.5686386

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

We microscopically investigate the dynamics of magnetic domains and domain walls induced by a current pulse in Permalloy narrow wires by means of Lorentz microscopy and simultaneous transport measurement. A variety of magnetic domain and domain wall dynamics are induced as a function of current density flowing into the wire and wire resistance. Important finding is that observed magnetic domain wall displacement and domain nucleation explicitly exhibit stochastic nature, indicating that the magnetic state in the wire is hardly controlled by using solely the current pulse. However, the application of small in-plane magnetic field changes drastically the nature into deterministic, which effectively improves controllability of the magnetic domain and domain wall dynamics using current.

DOI： 10.1109/TENCON.2010.5685851

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Magneto-transport prosperities of the Gd film and wire have been investigated. Negative magnetoresistances due to the reduction of the spin entropy were observed at various temperatures. The magnetoresistance changes were found to depend on the direction of the in-plane magnetic field at low temperature because of the Lorenz magnetoresistance effect. The strong spin current absorption effect into the Gd was also found.

DOI： 10.1109/TENCON.2010.5686393

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

We have investigated the cleaning condition of the Permalloy (Py) surface optimized for the efficient pure spin current injection in Py/Cu lateral spin valve structure. The efficiency of the spin injection is found to depend on the beam voltage and milling time strongly. The post annealing is also found to improve the spin injection efficiency.

DOI： 10.1109/TENCON.2010.5685852

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the injection of a pure spin current into a non-magnetic Cu wire in a lateral spin valve. We detect the spin accumulation occurring at the interfaces between the magnetic nanopillars and the non-magnetic wire in the non-local geometry. We confirm that the accumulated spins diffuse equally in the Cu wire irrespective of the presence of a charge current. The inversion of the injector and detector magnetic nanopillars does not affect the spin signal, in agreement with analytical predictions for this system.

DOI： 10.1016/j.jmmm.2009.07.045

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the injection of a pure spin current into a non-magnetic Cu wire in a lateral spin valve. We detect the spin accumulation occurring at the interfaces between the magnetic nanopillars and the non-magnetic wire in the non-local geometry. We confirm that the accumulated spins diffuse equally in the Cu wire irrespective of the presence of a charge current. The inversion of the injector and detector magnetic nanopillars does not affect the spin signal, in agreement with analytical predictions for this system. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2009.07.045

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this paper, we present the coherent suppression of precessional dynamics in a Ni₈₁Fe₁₉ (permalloy) microwire of 12-μm width and 100-μm length in presence of multiple spin-wave modes. The lateral confinement of the microwire causes spin-wave modes of frequencies very close to each other and local suppression of the modes were experimentally achieved with field pulses of slightly different durations but with the same rise time and fall time. Analysis shows that application of the pulsed field causes a large angle reorientation of the magnetization followed by a precession. The termination of the pulsed field at around 500 ps causes the magnetization to return back to the equilibrium position and to align parallel to the effective field so that the torque on the magnetization vanishes. However, this applies only to localized regions due to the presence of spin-wave modes of slightly different frequencies. Pulses of slight under or overwidth cause the precession to continue at a slightly different frequency suggesting that the spin-wave modes are not truly localized but there are overlapping regions where one mode dominates. When the dominating mode is partially suppressed, the relative amplitude of the modes changes significantly and the overall power spectrum peaks at a slightly different frequency.

DOI： 10.1109/TMAG.2009.2023995

記述言語：日本語  

27aRA-6 Current-induced magnetic domain nucleation in anisotropic Permalloy nanowires

記述言語：日本語  

25pPSA-23 Hanle effect in lateral spin valve with different ferro-magnetic electrodes

記述言語：日本語  

26aVD-1 Spin Hall effect in superconducting wires

記述言語：日本語  

25pPSA-33 Extrinsic Spin Hall Effect in CuIr wire

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A highly precise adaptive optical system that can be used in the hard X-ray region was developed. To achieve highly precise control of the wavefront shape, we discussed an optical system with a bendable mirror of deformation accuracy better than 0.4nm RMS. Using the system, we demonstrated the controllability of the wavefront of a 15nm hard X-ray nanobeam. The intensity profile of the wavefrontmodified beam was in good agreement with the wave-optically calculated profile.

DOI： 10.1143/JJAP.48.072503

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The spin Hall effect in molybdenum wires has been experimentally investigated by means of spin absorption method using lateral spin valve structure. The spin Hall conductivity of Mo wire is negative and decreases with increasing the resistivity. These tendencies are surprisingly consistent with the recent theoretical calculation based on the intrinsic spin Hall effect.

DOI： 10.1063/1.3076145

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Under electrical injection, spin accumulation occurs in lateral spin valves at the two ferromagnet/nonmagnet interfaces, which produces a torque on the ferromagnetic electrodes, and the possibility of pure spin-current-induced magnetization reversal. Here, we generate a pure spin current in a lateral spin valve while simultaneously sweeping an external magnetic field. We observe changes to the switching properties in accordance with the effective spin torque. We also find that the spin current necessary for magnetization reversal is much lower than that required in the absence of an external field, indicative that the effective potential barrier to be overcome is lowered by the applied magnetic field. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3058621]

DOI： 10.1063/1.3058621

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The spin Hall effect in molybdenum wires has been experimentally investigated by means of spin absorption method using lateral spin valve structure. The spin Hall conductivity of Mo wire is negative and decreases with increasing the resistivity. These tendencies are surprisingly consistent with the recent theoretical calculation based on the intrinsic spin Hall effect. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3076145]

DOI： 10.1063/1.3076145

記述言語：日本語  

27aTF-9 Detection of vortex translational resonance of magnetically coupled nanomagnets by means of spin torque diode effects

記述言語：日本語  

27pTF-3 Influence of interface resistance on Hanle effect in lateral spin valves

記述言語：日本語  

27aTF-11 Static and Dynamic Properties of Magnetic Vortex in Asymmetric Magnetic Disk

記述言語：日本語  

27aTF-5 Spin relaxation and spin Hall effect of non-magnetic metals

記述言語：日本語  

Spin Hall Effect in Spintronics

記述言語：その他   掲載種別：研究論文（その他学術会議資料等）  

We evaluated the magneto-optical properties of spin-valve (SV) stacks with perpendicular magnets comprised of a Gd-Fe (4-30 nm) free layer and a Tb-Fe-Co/CoFe pinned layer, and the spin-transfer switching properties of current-perpendicular-to-plane (CPP) SVs with the perpendicular magnets. The Gd-Fe free layer had polar Kerr rotation θ of 0.12° at a thickness of 10 nm. The θ reduced with a decrease in GdFe thickness and the sign of θ switched from positive to negative at a Gd-Fe thickness of 6 nm or thinner. Coercivity (H ) was maximum and saturation magnetization (M ) was minimum at a thickness of 8 nm. These phenomena may be explained by an inhomogeneous Gd-Fe composition. The CPP spin valves with the Gd-Fe (10 nm) free layer had a magneto-resistance (MR) of 0.038&#37;. The free layer of a CPP SV device was switched by a pulsed current, which exhibited intrinsic switching current densities of J = -3.3 × 10 A/cm and J = 4.3 × 10 A/cm with a thermal stability of 75, which is above the required value of 40. Perpendicular magnets are very useful for obtaining large magneto-optical signals from nano-magnets driven by spin-transfer switching. © 2008 IEEE. k k k c s c0-P-AP c0-AP-P 7 2 7 2

DOI： 10.1109/TMAG.2008.2002615

記述言語：日本語  

21pQG-1 Magnetization state change in Permalloy nanowires subject to current

記述言語：日本語  

21pPSA-17 Experimental expoloration into the origin of the spin Hall effect in transition metals

記述言語：日本語  

22pQG-1 Spin transports in ferromagnetic/nonmagnetic hybrid structures with planar configurations

記述言語：日本語  

22pQG-2 Relaxation processes of spin-injection-induced quasi-particles in superconducting wires

記述言語：日本語  

29pPSA-20 Influence of ferromagnetic ohmic contact on Hanle effect in a nonmagnetic wire

記述言語：日本語  

21pPSA-21 Detection of ferromagnetic resonance of a single nanomagnet by means of galvanomagnetic effects

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Laterally configured ferromagnetic/nonmagnetic multiterminal structures have great potential for developing future spintronic devices. We demonstrate two kinds of novel spintronic devices. One is a lateral spin valve with noncollinear dual spin injectors by which the direction of the spin accumulation in a nonmagnetic metal can be changed by varying the currents injected by two spin injectors. The other is a transformer between spin and charge currents using the spin Hall effect. A large spin Hall conductivity of 260 S/cm at room temperature, which is 10(4) times larger than that in semiconductor systems, is found in the Pt wire. We also demonstrate the reciprocal relation between the spin and charge currents. Temperature dependence of the spin Hall conductivity is also discussed.

DOI： 10.1109/TMAG.2008.924535

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the local magnetization process in a 100-nm-wide Permalloy/CoO exchange-coupled wire by means of nonlocal spin valve measurements for a structure with lateral geometry. The domain structure in the exchange-coupled wire is found to change with the direction of the exchange bias. When the exchange bias is parallel to the easy axis of the Permalloy wire, the magnetization-reversal process can be expressed by the single domain model. However, when the exchange bias is perpendicular to the easy axis, the magnetization reversal is accompanied by domain nucleation and annihilation processes even in the lateral dimension of 100 nm. The reason for the dependence of the domain structure on the direction of the exchange bias is discussed. (c) 2008 American Institute of Physics.

DOI： 10.1063/1.2903509

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Spin currents absorption effect into a Pt wire is demonstrated by mean of the nonlocal spin valve measurement. Using this absorption effect, an inverse spin Hall effect is successively observed at room temperature. Moreover, the direct spin Hall effect is also demonstrated by a Pt spin current generator with nonlocal detection technique. The spin Hall conductivity in the Pt wire is 260 S/cm at room temperature, which is 10(4) times larger than that in semiconductor systems. Temperature dependence of the spin Hall conductivity is also investigated. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2832665

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated dynamics of paired domain walls in a microfabricated ferromagnetic ring by using a ballistic transport character of a two-dimensional electron gas (2DEG) microcross. The stray field from the domain walls results in a change in the bend resistance of the 2DEG cross lying beneath the ferromagnetic ring depending on the positions of the domain walls. The measurements for different directional angles of the applied magnetic field reveal that the domain wall behavior is strongly affected by identical local defects in the ring. We have also studied a response of paired domain walls under a pulsed magnetic field. We find that the paired domain walls switch the positions without annihilation under a pulsed magnetic field with a short rise time. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2007.08.031

記述言語：日本語  

24aWL-3 Temperature dependence of spin diffusion in nonmagnetic metal

記述言語：日本語  

23pWL-1 Spin Hall effect in normal and superconducting Nb wire

記述言語：日本語  

23pWL-15 Thermal conductance dependence of current-excited magnetization dynamics

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated superconductive properties of nano-scale Nb wires fabricated by a simple lift-off process with magnetron sputtering. The superconductive properties of the Nb wires were remarkably improved by employing highly plasma resistant electron-beam resist ZEP520A combined with a thin Ti passivation layer. This optimized fabrication process yielded a 300-nm-wide Nb wire with the same transition temperature as that of the reference Nb film. Thereby, a highly transparent Nb/Cu junction was successfully fabricated. (c) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.021701

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Temperature dependence of spin relaxation process in a Cu wire has been studied by means of nonlocal spin-valve measurements. The spin-diffusion length of the Cu wire is found to take maximum at the characteristic temperature, below which the spin-diffusion length is reduced. The mechanism of the reduction can be explained by considering the spin-flip scattering due to the oxidized surface of the Cu wire. The thickness dependence of the characteristic temperature supports the interpretation with the surface oxidation.

DOI： 10.1103/PhysRevLett.100.066602

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We microscopically demonstrate that the magnetic domain is controllably nucleated and erased in the uniformly magnetized wire using a current pulse in small magnetic fields. Lorentz microscopy is performed in Permalloy nanowires with in-plane anisotropy. The stochastic nature of the magnetization reversal due to spin wave and thermal excitations in the absence of magnetic field completely disappears and turns into deterministic in the presence of small magnetic field, which enables the magnetization reversal control. We interpret that the phenomena are associated with Zeeman energy stabilization. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2828865

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have studied the evolution of the spin Hall effect (SHE) in the regime where the material size responsible for the spin accumulation is either smaller or larger than the spin diffusion length. Lateral spin valve structures with Pt insertions were successfully used to measure the spin absorption efficiency as well as the spin accumulation in Pt induced through the spin Hall effect. Under a constant applied current the results show a decrease of the spin accumulation signal is more pronounced as the Pt thickness exceeds the spin diffusion length. This implies that the spin accumulation originates from bulk scattering inside the Pt wire and the spin diffusion length limits the SHE. We have also analyzed the temperature variation of the spin Hall conductivity to identify the dominant scattering mechanism.

DOI： 10.1103/PhysRevLett.99.226604

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Vertical stacks of two Co rings with deep submicron lateral sizes and different thicknesses are fabricated and studied. The experimental results suggest the existence of a metastable domain wall structure revealed by the micromagnetics simulation. The technologically important vortex-vortex switching is found dominated by the annular Oersted field of perpendicularly injected dc, but also significantly affected by the spin-transfer torque. The efficiency of the spin-transfer torque and the switching process are discussed.

DOI： 10.1103/PhysRevB.76.172401

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A large spin accumulation due to the electrical spin injection has been observed in Permalloy-silver lateral spin-valve structures. The observed resistance change is the largest among the reported metallic lateral spin valves with Ohmic junctions. The spin-diffusion length deduced from the experimental results is also found to be the longest among the normal metals reported so far. All the results can be quantitatively explained by the common spin-diffusion model without any discrepancies unlike the results of Godfrey and Johnson.

DOI： 10.1103/PhysRevLett.99.196604

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We are able to continuously change the direction of polarization of spin accumulation in a nonmagnetic metal by varying the currents injected by two ferromagnetic spin injectors. From measurements made at a distance from the injection area, we find a cos phi variation of the spin signal. This confirms that the angle of polarization of the nonlocal spin polarization with respect to the magnetization of the fixed spin detector is continuously varied as we change the injection currents. We give an explanation for the origin of this simple cos phi variation of the spin signal.

DOI： 10.1103/PhysRevLett.99.166601

記述言語：日本語  

22pWB-3 Current-excitated domain nucleation and annihilation in uniformly magnetized state

記述言語：日本語  

21pPSB-72 Effect of spin accumulation on nonmagnetic/superconducting junction characteristics

記述言語：日本語  

Generation of Spin Currents and Magnetization Reversal by Means of Non-Local Technique

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The authors have investigated dynamics of paired domain walls in a ferromagnetic ring circuit, driven by a variable pulsed magnetic field. The magnetic reversal accompanied by the propagations of the domain walls depends not only on the amplitude but also on the rise time of the applied pulsed magnetic field. The threshold of the rise time is found comparable to the propagation time of a domain wall along a half-path of the ring. This finding may be useful for the high speed operation of the magnetic logic devices based on the domain wall motion. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2748339

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the magnetization process of a 200-nm-wide Permalloy ring using a nonlocal spin-valve measurement technique in a lateral geometry. The nonlocal spin signal is found to reveal the chirality of the flux closure state in the magnetic ring. The angular dependence of the magnetization process of the Permalloy ring are also studied. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2745311

記述言語：英語  

DOI： 10.1103/PhysRevLett.98.249901

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Reversible spin Hall effect comprising the direct and inverse spin Hall effects was electrically detected at room temperature. A platinum wire with a strong spin-orbit interaction is used not only as a spin current absorber but also as a spin-current source in the specially designed lateral structure. The obtained spin Hall conductivities are 2: 4 x 10(4) (Omega m)(-1) at room temperature, 10(4) times larger than the previously reported values of semiconductor systems. Spin Hall conductivities obtained from both the direct and inverse spin Hall effects are experimentally confirmed to be the same, demonstrating the Onsager reciprocal relations between spin and charge currents.

DOI： 10.1103/PhysRevLett.98.156601

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Laterally configured ferromagnetic/nonmagnetic multi-terminal spintronic devices enable the performance of detailed study of spin accumulation in nonmagnets. The spin diffusion processes in lateral structures are investigated using nonlocal spin injection techniques. Efficient spin injection and detection are accomplished by optimizing the probe configuration and junction structures on the basis of the concept of spin resistance. The magnetization switching of a nanoscale ferromagnet is finally realized using efficient spin current absorption behaviour induced by nonlocal spin injection.

DOI： 10.1088/0953-8984/19/16/165216

記述言語：英語  

The authors investigate the influence of the vortex chirality on the magnetization processes of a magnetostatically coupled pair of magnetic disks. The magnetic vortices with opposite chiralities are realized by introducing asymmetry into the disks. The motion of the paired vortices are studied by measuring the magnetoresistance with a lock-in resistance bridge technique. The vortex annihilation process is found to depend on the moving directions of the magnetic vortices. The experimental results are well reproduced by the micromagnetic simulation. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2716861

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jmmm.2006.10.909

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The domain formation induced by perpendicular spin injection has been studied with the magnetic nanopillar structure. When the bottom layer is an unpatterned thin film, an intermediate state is observed and characterized to be a domain formed in the bottom layer. Domain formation is also investigated when the size of the top nanomagnet is increased. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.931

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The influence of the pure spin current injection on a domain wall nucleation process in a magnetic wire is investigated by using the nonlocal spin injection technique. The pure spin current injection is found to assist the domain wall nucleation. The spin current responsible for nucleating the domain wall in the nonlocal configuration is comparable to the threshold spin current for the domain wall displacement in the direct current injection. The bias-field dependence of the switching current shows a complicated behaviour. This may be related to the detailed domain structure in the vicinity of the domain wall.

DOI： 10.1088/0022-3727/40/5/S14

記述言語：日本語  

19pZC-4 Inverse spin Hall effect in ferromagnetic/normal-metal junction

記述言語：日本語  

18aPS-41 Spin Hall effect and anomalous Hall effect in a ferromagnetic permalloy nano-wire

記述言語：日本語  

18pZC-11 Direct observation of current-driven magnetization dynamics using Lorentz microscopy

記述言語：日本語  

18pZC-12 Current-excitated domain nucleation and annihilation in uniformly magnetized state

記述言語：英語  

19pZC-2 Electrical characterization of spin Hall effect in Pt-based nanostructures

記述言語：日本語  

19pZC-3 Spin-current absrobtion and spin Hall effect in a Gold nano wire

記述言語：日本語  

19pZC-8 Spin-Current Interference in a Cu Nano-Ring

記述言語：日本語  

18aPS-33 Local Magnetization Measurement of Vortex Nucleation and Annihilation Processes in Ferromagnetic Disks

記述言語：日本語  

18aPS-34 Spin transfer induced magnetic vortex dynamics observed by planar Hall effect

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The authors fabricated a current-perpendicular-to-plane pseudo-spin-valve nanopillar comprising a thick and a thin Co rings with deep submicron lateral sizes. The dc current can effectively induce the flux-closure vortex states in the rings with desired chiralities. Abrupt transitions between the vortex states are also realized by the dc current and detected with the giant magnetoresistance effect. Both Oersted field and spin-transfer torque are found important to the magnetic transitions, but the former is dominant. They can be designed to cooperate with each other in the vortex-to-vortex transitions by carefully setting the chirality of the vortex state in the thick Co ring. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2710185

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The authors fabricated Co nanorings incorporated in the vertical pseudo-spin-valve nanopillar structures with deep submicron lateral sizes. It is shown that the current-perpendicular-to-plane giant magnetoresistance can be used to characterize a very small magnetic nanoring effectively. Both the onion state and the flux-closure vortex state are observed. The Co nanorings can be switched between the onion states as well as between onion and vortex states not only by the external field but also by the perpendicularly injected dc current.

DOI： 10.1063/1.2431471

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the current-driven magnetization dynamics in narrow Permalloy wires by means of Lorentz microscopy and electron holography. Current pulses are found to transform the magnetic structure in the uniformly magnetized state below the Curie temperature. A variety of magnetic states including reversed magnetic domains are randomly obtained in low probability. The dynamics of vortices found in most of observed magnetic states seems to play a key role in triggering the magnetization reversal.

DOI： 10.1143/JJAP.45.L1322

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The temperature dependence of the switching current of a magnetic nanopillar is investigated from 10 to 290 K. According to the switching probability measurement with the pulsed current, and the differential resistance measurement with sweeping the dc current, the intrinsic switching currents increase with decreasing the temperature. Transport calculations show that this temperature dependence is closely related to the reduced spin accumulation and spin polarization of the electrical current at low temperatures, attributed to the varied transport parameters. The conclusion is in accordance with the temperature dependence of the resistance difference between antiparallel and parallel magnetic configurations. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2420789

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Magnetically coupled domain wall pinning has been investigated by means of an attached pair of ferromagnetic wires. The magnetic configuration of the paired wires (parallel or antiparallel) can be controlled by applying an external magnetic field along the wires. The strength of the pinning due to the magnetic interaction between the domain wall and the paired wires shows a significant difference between the parallel and antiparallel configurations, which is well reproduced by a micromagnetics simulation.

DOI： 10.1063/1.2385224

記述言語：英語   掲載種別：研究論文（学術雑誌）  

With the experimental results obtained with a special nanopillar structure and the calculations based on the one-dimensional diffusion equations, the respective contributions to the spin torque from spin accumulation and local spin current are quantitatively deduced. The results for a typical nanopillar structure show that the spin accumulation contributes to about 90&#37; of the necessary torque for the antiparallel to parallel switching, while the parallel to antiparallel switching is totally dominated by the local spin current. Both the variations in spin accumulation and local spin current should be considered in any effort to reduce the critical switching current density. However it seems more effective to increase the local spin current in most cases.

DOI： 10.1103/PhysRevB.74.153301

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A special nanopillar comprised of a thick top ferromagnetic layer and a thin bottom ferromagnetic layer is fabricated and the transport properties are measured by applying a dc current and an external field. It is shown experimentally that the dc current flowing through the nanopillar could lead to intermediate states between the antiparallel and the parallel magnetic configurations. The intermediate states are characterized to be the result of domain formation in the bottom ferromagnetic layer, due to the injection of spin-polarized current. The results verify that the spin-transfer effect may induce domain formation in a magnetic thin film. It is also suggested that when the spin-transfer effect is utilized to switch the nanopillar device, the domain formation may result in the incomplete magnetization switching. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2357002

記述言語：日本語  

23pXH-3 Spin torque exerting on a magnetic vortex structure with a controlled gyro vector

記述言語：日本語  

23aPS-17 Magneto-transport properties in NiFe/Cu and Co/Cu lateral spin valves

記述言語：日本語  

23pXH-1 Spin-Current Interference in a Cu Nano-Ring

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the current-excited magnetization dynamics in a narrow ferromagnetic Permalloy wire by means of Lorentz microscopy, together with the results of simultaneous transport measurements. A detailed structural evolution of the magnetization is presented as a function of the applied current density. Local structural deformation, bidirectional displacement, and magnetization reversal are found below the Curie temperature with increasing the current density. We discuss probable mechanisms of observed features of the current-excited magnetization dynamics.

DOI： 10.1143/JJAP.45.L683

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The induced motion of a magnetic vortex in a micron-sized ferromagnetic disk due to the dc current injection is studied by measuring planar Hall effect. We demonstrated that the vortex motion induced by the dc current injection has no threshold current and is proportional to the injecting current. The induced displacement deduced from the change in planar Hall resistance is quantitatively consistent with theoretical predictions. The dc current injection is also found to induce the spin torque that sweeps the vortex out of the disk at the critical current while bias magnetic fields are applied. Peak structures similar to those originated from spin wave excitations are observed in the differential planar Hall resistance curve.

DOI： 10.1103/PhysRevB.74.014424

記述言語：英語   掲載種別：研究論文（学術雑誌）  

To clarify the contributions of spin-polarized current and spin accumulation to the current-induced magnetization switching, the effects of the top electrode size of the magnetic nanopillar are investigated both theoretically and experimentally. Theoretical calculation demonstrates that the spin-polarized current and the spin accumulation can be adjusted in opposite directions by modifying the size of the top electrode. Increase in the size of the top electrode suppresses the spin accumulation but enhances the spin-polarized current inside the nanopillar. On the other hand, it is shown experimentally that the nanopillar with a wide top electrode exhibits small critical switching current compared to the nanopillar with a narrow top electrode. The results suggest that the spin-polarized current contributes to the current-induced magnetization switching dominantly over the spin accumulation. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2005.07.013

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The junction size dependence of the spin accumulation in a nonmagnet is studied by using lateral spin valves geometry consisting of the Py/Cu ohmic junctions. We experimentally demonstrate that reducing the size of the junction drastically improves the efficiency of the spin injection into the Cu wire because of the enhancement of the spin resistance for the Py wire. The spin polarization in the Cu wire increases exponentially with reducing the junction area irrespective of the same spacing between the injector and the detector. The junction size dependence of the spin signal yields the spin diffusion lengths and the spin polarization which are reasonable values compared with previous experiments.

DOI： 10.1103/PhysRevB.73.132405

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Nonlocal spin-valve configuration is used for spin current injection into a nanoscale ferromagnetic particle to reverse its magnetization. The nonlocal spin injection aligns the magnetization of the nanoscale particle along the spin injector, whereas the reverse switching is hardly observed up to the available maximum exciting current of about 15 mA. This asymmetric behavior implies the presence of asymmetric barrier formed in the vicinity of the interface. The magnitude of the essential spin current for the reversal is determined to be about 160 mu A, on the reasonable order of magnitude compared with the experimental values for conventional pillar structures. (C) 2006 American Institute of Physics.

DOI： 10.1063/1.2162031

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Taking into account the thermal effect, we verify that the strong spin relaxation in the capping layer of a magnetic nanopillar significantly affects the current-induced magnetization switching behavior by reducing the critical switching current density. Theoretical calculations reveal that increasing the spin relaxation in the capping layer enhances the spin-polarized current while suppresses the contribution of the spin accumulation to the magnetization switching. The results suggest that the spin-polarized current, rather than the spin accumulation, dominates the current-induced magnetization switching. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2189205

記述言語：日本語  

29pSC-9 Rotational dynamics of paired nano-domain walls confined in an elliptical ring

記述言語：日本語  

28pSC-6 Quantum Spin Interference in a Cu Nano-Ring

記述言語：日本語  

28pSC-8 Control of spin accumulation in nonmagnet by dual ferromagnetic injectors

記述言語：日本語  

29pSC-7 Control of magnetization structure of concatenate micro-scale magnetic disks under spin current injection

記述言語：日本語  

Manipulation of magnetization state using spin current

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have performed nonlocal spin injection into a nanoscale ferromagnetic particle configured in a lateral spin-valve structure to switch its magnetization only by spin current. The nonlocal spin injection aligns the magnetization of the particle parallel to the magnetization of the spin injector. The spin current responsible for switching is estimated from the experiment to be about 200 mu A, which is reasonable compared with the values obtained for conventional pillar structures. Interestingly, the switching always occurs from antiparallel to parallel in the particle-injector magnetic configurations, where no opposite switching is observed. Possible reasons for this discrepancy are discussed.

DOI： 10.1103/PhysRevLett.96.037201

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrate the determination of the vortex chirality using a nonlocal spin-valve measurement technique in a lateral spin valve consisting of a Permalloy (Py) disk 1 mu m in diameter and a Py wire 100 nm in width. The vortex chirality is determined under two probe configurations; the disk as the current probe and the disk as the voltage probe. The vortex chirality is found to depend on the probe configuration because of the current-induced Oersted field. (C) 2005 American Institute of Physics.

DOI： 10.1063/1.2120911

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Magnetic nanopillars with variable top electrodes were fabricated to clarify the roles of the spin current and the spin accumulation in the current-induced magnetic switching. The critical switching current is significantly increased when the size of the top electrode is comparable to that of the nanopillar. This result implies that the dominant contribution in the current-induced magnetic switching is not the spin accumulation, but the spin current. (C) 2005 American Institute of Physics.

DOI： 10.1063/1.2093921

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the influence of An capping layer on the spin accumulation in a lateral spin valve consisting of Permalloy and Cu wires. The nonlocal spin valve measurements show that the An capping significantly suppresses the spin accumulation in the Cu wire, although it improves the electrical conductivity. This is understood as a result of the small spin-flip resistance of An whereby absorbed spins are successively flipped.

DOI： 10.1109/TMAG.2005.854799

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We present a formalism to determine the three-dimensional (3D) distribution of the spin-polarized current and electrochemical potential inside arbitrary nanostructures such as magnetic/nonmagnetic layered pillars, etc. The model is based on dividing the nanostructure into a 3D electric circuit of spin-dependent-resistor elements, inside each of which the propagation is treated as a one-dimensional problem. The solutions presented here are calculated in the diffusive transport regime for the parallel/antiparallel magnetic states. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.2037868

記述言語：日本語  

19pYB-1 Magnetic domain wall pinning by using switchable magnetic gate

記述言語：日本語  

19aYB-5 Probe-configuration dependence of the spin signal in lateral spin valve structure

記述言語：日本語  

21pPSA-3 Magnetization process of micro-scale magnetic disk under spin current injection

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrate the method to calculate the spatial distributions of the spin current and accumulation in the multiterminal ferromagnetic/nonmagnetic hybrid structure using an approximate electrotransmission line. The analyses based on the obtained equation yield the results, in good agreement with the experimental ones. This implies that the method allows us to determine the spin diffusion length of an additionally connected electrically floating wire from the reduction of the spin signal.

DOI： 10.1103/PhysRevB.72.014461

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report that the inhomogeneous spin accumulation in a nonmagnetic layer induces the spin-polarized current flowing in a detector ferromagnetic strip lying underneath the nonmagnetic layer. In Ni-Fe/Cu planar spin-valve structures, the induced spin-polarized current causes the spin-valve-like signal in the Ni-Fe wire without any boundary resistance in the Cu/Ni-Fe junction. The relation between the inhomogeneous spin accumulation and the magnitude of the induced spin-valve-like signal is investigated by varying the width of the Cu wire. (C) 2005 American Institute of Physics.

DOI： 10.1063/1.1883717

記述言語：日本語  

Laterally nanostructured ferromagnetic / nonmagnetic hybrid multi-terminal devices are potential spintronic devices, and allow detailed study of the spin accumulation in non-magnetic layers. We investigate the dependence of the spin signal in the non-local spinvalve configuration on the width of the Cu strip and the influence of an additional Permalloy ohmic contact on the spin signal in lateral spin-valve structures consisting of Py/Cu ohmic junctions. We also report the non-local Hall resistance measurements, which reflect the spin current in the non-magnetic layer.

記述言語：日本語  

25aXN-4 Enhancement of spin signal in lateral spin-valve structure

記述言語：日本語  

25aXN-7 Detection of magnetization process in a small ferromagnetic ring by using semiconductor two-dimensional electron system

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated experimentally the nonlocal voltage signal (NLVS) in the lateral Permalloy (Py)/Cu/Py spin-valve devices with different width of Cu stripes. We found that NLVS strongly depends on the distribution of the spin-polarized current inside Cu strip in the vicinity of the Py detector. To explain these data we have developed a diffusion model describing spatial (three dimensional) distribution of the spin-polarized current in the device. The results of our calculations show that NLVS is decreased by a factor of 10 due to spin flip scattering occurring at the Py/Cu interface. The interface resistivity on the Py/Cu interface is also present, but its contribution to reduction of NLVS is minor. We also found that most of the spin-polarized current is injected within the region 30 nm from the Py injector/Cu interface. In the area at Py detector/Cu interface, the spin-polarized current is found to flow mainly close on the injector side, with 1/e exponential decay in the magnitude within the distance 80 nm.

DOI： 10.1103/PhysRevB.71.094402

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Within diffusive transport, we calculate three-dimensional current distribution inside a (Cu/Co) pillar structure, where the pillar is terminated either by an infinitely large Cu layer, or by a Cu wire with a cross-sectional area identical to that of the pillar. We study how pillar terminations (infinitely large or finite) influence the magnitudes and inhomogeneities of the spin-polarized current and electrochemical potential. We found that infinitely large Cu layers work as strong spin scatterers, increasing the magnitude of spin-polarized current inside the pillar twice and reducing spin accumulation to nearly zero. The inhomogeneities of the electrochemical potential are found to be much smaller than those of the spin-polarized current.

DOI： 10.1103/PhysRevB.71.094434

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Within diffusive transport, we calculate three-dimensional current distribution inside a (Cu/Co) pillar structure, where the pillar is terminated either by an infinitely large Cu layer, or by a Cu wire with a cross-sectional area identical to that of the pillar. We study how pillar terminations (infinitely large or finite) influence the magnitudes and inhomogeneities of the spin-polarized current and electrochemical potential. We found that infinitely large Cu layers work as strong spin scatterers, increasing the magnitude of spin-polarized current inside the pillar twice and reducing spin accumulation to nearly zero. The inhomogeneities of the electrochemical potential are found to be much smaller than those of the spin-polarized current. ©2005 The American Physical Society.

DOI： 10.1103/PhysRevB.71.094434

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A nanoscale pillar consisting of a Co/Cu/Co layered structure was fabricated by means of electron-beam lithography to study perpendicular transport properties as a function of both dc electric currents and applied magnetic fields. The nanopillar exhibits sharp transitions in magnetoresistance associated with magnetization reversal between antiparallel and parallel configurations of the two Co layers. Remarked is that the application of a large initializing field of 1 kOe and a current of 16 mA prior to the measurement results in an intermediate state. This intermediate state seems nucleated due to the spin wave instability. (C) 2005 American Institute of Physics.

DOI： 10.1063/1.1863431

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the dependance of the spin signal in a lateral spin-valve structure Ni-Fe/Cu ohmic junction on the probe configuration. The spin-valve signal is strongly affected by probe configuration because of the non-uniform spin-current distribution due to a wide non-magnetic probe. (C) 2004 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2004.09.043

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We propose a nonlocal spin-valve measurement combined with a local spin-valve structure to enlarge spin signal. The probe configuration consists of a lateral spin valve with three Ni-Fe wires bridged by a Cu wire. The advantage is that the spin polarization in the Cu wire induced by the spin injection can be enhanced compared to the conventional method. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1829772

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the detection of clear spin-valve signal without any spurious magnetoresistive signal in a lateral spin-valve structure consisting of Cu/Ni-Fe ohmic junction using local current injection. The obtained spin-valve signal is much larger than that of the nonlocal spin-valve configuration because of the efficient spin accumulation. The local current injection experiments with different probe configurations proved that the spin-valve signal is caused by the spin-dependent boundary resistance at the interface between the ferromagnetic voltage probe and the spin-polarized nonmagnetic wire. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1805698

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We experimentally demonstrate that the ohmic contact of a Ni-Fe wire additionally connected to a Cu strip between an injector and detector in a nonlocal spin-valve structure signicantly suppresses the spin polarization induced in the Cu strip. This behavior is attributable to spin current absorption into the connected additional Ni-Fe wire. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1811801

記述言語：日本語  

13pWB-1 Spin Accumulation and Spin-Flip Resistance in Lateral Spin Valve

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We here experimentally demonstrate the domain wall depinning triggered by injecting the current into the domain wall. The domain wall is pinned at the connection of a large pad and a narrow wire prior to the current injection experiment. The pinned domain wall is freed and pushed into the wire at the critical current, only when the current is injected along the direction of the domain wall propagation. These results imply that the injection of the spin-polarized current into the domain wall causes additional magnetic pressure due to the spin-momentum transfer between the spin-olarized current and the localized magnetic moment. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.205

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We here demonstrate the measurement of the non-local Hall resistance which reflects the spatial distribution of non-equilibrium magnetization induced in the nano-scale normal metal Cu/ferromagnetic Ni-Fe alloy junction. The non-local Hall resistance seems to vary proportional to the perpendicular component of the injected spin current. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.197

記述言語：日本語  

27pXJ-5 Spin accumulation measured in the non-local configuration

記述言語：日本語  

We describe the detailed design of a highly sensitive magnetometer based on micro-magneto-optical Kerr effect (MOKE) magnetometry, consisting of an optical microscope combined with an ordinary MOKE set-up. The system enables microscopic MOKE hysteresis loops to be measured with a spatial resolution 10^4 times better than that of conventional longitudinal MOKE magnetometry. The sensitivity of the system is demonstrated by measuring MOKE hysteresis curves of submicron permalloy rectangular dots and wires.

記述言語：日本語  

Measurement of Spin Accumulation in Non-Local Configuration

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrate experimentally the domain-wall depinning triggered by injecting the polarized spin current into the domain wall. The domain wall is pinned at the junction of a large pad and a narrow wire prior to the current injection experiment. When the polarized spin current is injected along the direction of the domain-wall propagation, the pinned domain wall is freed and pushed into the wire at the critical current that monotonously decreases by increasing the applied bias magnetic field. These results imply that the injection of the spin-polarized current into the domain wall causes additional magnetic pressure due to the spin-momentum transfer between the spin-polarized current and the localized magnetic moment. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1629150

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the influence of the dc current injection on trapped domain walls in magnetic nanostructures designed for high precision anisotropy magnetoresistance measurements. The results obtained for a simple strip with no trapped domain wall are compared with those for the strip with the trapped domain wall. The depinning field of the domain wall decreases significantly when the electron current is applied along the direction of the domain wall propagation. On the other hand, the switching field only shows a small reduction when the electron current is opposed to the domain wall propagation. The origin of this behavior can be explained by considering Joule heat as well as an additional pressure exerted on the domain wall due to the transfer of the spin angular momentum from the spin-polarized current to the local magnetic moment. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1618941

記述言語：日本語  

Domain wall depinning in a magnetic wire due to spin polarized current

記述言語：日本語  

Spin Hall effect in ferromagneto/nonmagneto small junctions

記述言語：日本語  

Non-local Hall effect in ferromagneto/nonmagneto small junctions

記述言語：日本語  

Non-local Hall effect in ferromagneto/nonmagneto small junctions

開催年月日： 2009年12月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：東北大学   国名：その他  

開催年月日： 2009年7月

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Karlsruhe   国名：ドイツ連邦共和国  

開催年月日： 2009年6月

記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

開催地：大阪大学   国名：日本国  

開催年月日： 2009年4月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：東京   国名：日本国  

開催年月日： 2009年3月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：九州大学   国名：日本国  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：日本語   会議種別：口頭発表（一般）  

記述言語：日本語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

掲載種別：記事・総説・解説・論説等（学術雑誌）  

掲載種別：記事・総説・解説・論説等（学術雑誌）  

掲載種別：記事・総説・解説・論説等（学術雑誌）