| 1. |
Yuichiro Kurokawa, Yusuke Tahara, Yuki Hamada, Masahiro Fujimoto, Hiromi Yuasa , Scalable spin Seebeck thermoelectric generation using Fe-oxide nanoparticle assembled film on flexible substrate, Scientific Reports, 12, p. 16605, 2022.10. |
| 2. |
Yuichiro Kurokawa, Keisuke Yamada, Tomohiro Taniguchi, Shu Horiike, Terumitsu Tanaka, Hiromi Yuasa, Ultra-wide-band millimeter-wave generator using spin torque oscillator with strong interlayer exchange couplings, Scientific Reports, 12, p.10849, 2022.07, Recent increased development interest in millimeter-wave oscillator devices has necessitated realization of small oscillators with high frequency, wide frequency tunability, and room-temperature operation. Spin-torque oscillators (STOs) are fascinating candidates for such applications because of their nanometer size and suitability for room-temperature operation. However, their oscillation frequency and tunable range are limited to the order of 100 MHz–10 GHz. Here, we propose use of bilinear (J1) and biquadratic (J2) interlayer exchange couplings between ferromagnets in STOs to overcome these problems. The bilinear coupling contributes to oscillation frequency enhancement, whereas the biquadratic coupling facilitates frequency tunability via a current. Using micromagnetic simulation with parameters estimated from a material with small saturation magnetization, for J1 = 0 and J2 = − 1.0 mJ/m^2, respectively, we find that the STO exhibits high frequency from 23 to 576 GHz and that its tunability reaches 61 GHz/(10^11 A/m^2) for current densities of − 0.5 to − 9.5 × 10^11 A/m^2. An analytical theory based on the macrospin model is also developed, which exhibits good quantitative agreement with the micromagnetic simulations. These results introduce new possibilities for spintronics applications in high-frequency devices such as next-generation mobile communications.. |
| 3. |
Shilei Ding, Andrew Ross, Romain Lebrun, Sven Becker, Kyujoon Lee, Isabella Boventer, Souvik Das, Yuichiro Kurokawa, Shruti Gupta, Jinbo Yang, Gerhard Jakob, and Mathias Kläui, Interfacial Dzyaloshinskii-Moriya interaction and chiral magnetic textures in a ferrimagnetic insulator, PHYSICAL REVIEW B, https://doi.org/10.1103/PhysRevB.100.100406, 100, 100406(R), 100, 100406(R) (2019), 2019.09, The interfacial Dzyaloshinskii-Moriya interaction (DMI) in multilayers of heavy metal and ferromagnetic metals enables the stabilization of novel chiral spin structures such as skyrmions. Magnetic insulators, on the other hand, can exhibit enhanced dynamics and properties such as lower magnetic damping and therefore it is of interest to combine the properties enabled by interfacial DMI with insulating systems. Here, we demonstrate the presence of interfacial DMI in heterostructures that include insulating magnetic layers. We use perpendicularly magnetized insulating thulium iron garnet (TmIG) films capped by the heavy metal platinum, grown on gadolinium gallium garnet (GGG) substrates, and find a surprisingly strong interfacial DMI that, combined with spin-orbit torque, results in efficient switching. The interfacial origin is confirmed through thickness-dependence measurements of the DMI, revealing the characteristic 1/thickness dependence. We combine chiral spin structures and spin-orbit torques for efficient switching and identify skyrmions that allow us to establish the GGG/TmIG interface as the possible origin of the DMI.. |
| 4. |
Yuichiro Kurokawa, Masakazu Wakae, Satoshi Sumi, Hiroyuki Awano, Kohei Ohnishi, Hiromi Yuasa, Spin-orbit torque-driven current-induced domain wall motion in Gd-Fe magnetic wires, Japanese Journal of Applied Physics, 10.7567/1347-4065/aafa91, 58, 3, 2019.03, We fabricated Gd-Fe/Ta/sub. and W/Gd-Fe/Ta/sub. perpendicular magnetized magnetic wires and investigated current-induced domain wall motion (CIDWM) in them. The propagation field of the Gd-Fe wires is low (∼3 mT), and the wires were found to have a low threshold current density (∼3.1 ×1010 A m-2) of CIDWM. The directions of the CIDWM in Gd-Fe/Ta and W/Gd-Fe/Ta wires are opposite to each other, indicating that the CIDWM in both wires is driven by spin-orbit torque because the spin Hall torque generated by the Ta underlayer and W cap layer oppose each other.. |
| 5. |
Masakazu Wakae, Yuichiro Kurokawa, Hiromi Yuasa, Observation of spin-orbit torque-induced magnetization switching in Gd-Fe perpendicular magnetized wire with in-plane exchange bias field, Japanese Journal of Applied Physics, 10.7567/1347-4065/aaf877, 58, 2019.01, We fabricated a Ta/Gd-Fe/Ta and a Ta/Gd-Fe/Ir22Mn78/Co90Fe10/Ta multilayered magnetic wire and investigated spin-orbit torque current-induced magnetization switching in these wires. Magnetization switching in the Ta/Gd-Fe/Ir22Mn78/Co90Fe10/Ta multilayered magnetic wire can be observed by an electric current even if the external in-plane magnetic field is not applied at all. Moreover, we successfully observed the periodical magnetization switching in the Ta/Gd-Fe/Ir22Mn78/Co90Fe10/Ta multilayered magnetic wire in zero magnetic field. This indicates that the present wire is a promising material to realize magnetic random access memory with low power consumption.. |
| 6. |
Yuichiro Kurokawa, Hiroyuki Awano, Multilayered current-induced domain wall motion in Pt/Tb-Co/Ta/Tb-Co/Pt magnetic wire, AIP ADVANCES, 10.1063/1.5017814, 8, 2, 2018.02, We fabricated a Pt (3 nm)/Tb0.28Co0.72 (4 nm)/Ta (4 nm)/Tb0.26Co0.74 (4 nm)/Pt
(3 nm) multilayered magnetic wire and investigated current-induced domain wall
motion within it.We found that the Hall resistance of the Pt/Tb-Co/Ta/Tb-Co/Pt wire
has four stable levels under a magnetic field of zero. Moreover, we observed that the
domain walls in both the upper and lower ferromagnetic layers are controlled by a
single current source. This indicates that Pt/Tb-Co/Ta/Tb-Co/Pt wire can be used in
multi-level magnetic wire memory.. |
| 7. |
Yuichiro Kurokawa, Akihiro Shibata, Hiroyuki Awano, Enhancement of spin orbit torques in a Tb-Co alloy magnetic wire by controlling its Tb composition, AIP ADVANCES, 10.1063/1.4974280, 7, 5, 2017.05. |
| 8. |
＠Yuichiro Kurokawa, Ryogo Yoshimura, Satoshi Sumi, Hiroyuki Awano, Thermal reduction of the threshold current density for current-induced domain wall motion in Tb-Co magnetic alloy wire, AIP ADVANCES, 10.1063/1.4979727, 7, 3, 2017.03. |
| 9. |
Yuichiro Kurokawa, Masaya Kawamoto, Hiroyuki Awano, Current-induced domain wall motion attributed to spin Hall effect and Dzyaloshinsky-Moriya interaction in Pt/GdFeCo (100 nm) magnetic wire, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.7567/JJAP.55.07MC02, 55, 7, 2016.07. |
| 10. |
Yuichiro Kurokawa, Takehiko Hihara, Ikuo Ichinose, Critical field of two-dimensional superconducting Sn1-x/Si x bimetallic composite cluster assembled films with energetic cluster impact deposition, Journal of Applied Physics, 10.1063/1.4798262, 113, 17, 2013.05. |
