Language：Others   Publishing type：Research paper (other academic)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.38.011081

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Language：Others   Publishing type：Research paper (other academic)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.38.011033

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Language：Others   Publishing type：Research paper (other academic)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.38.011098

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of the National Academy of Sciences of the United States of America  

While the effective g-factor can be anisotropic due to the spin-orbit interaction (SOI), its existence in solids cannot be simply asserted from a band structure, which hinders progress on studies from such viewpoints. The effective g-factor in bismuth (Bi) is largely anisotropic; especially for holes at T-point, the effective g-factor perpendicular to the trigonal axis is negligibly small (<0.112), whereas the effective g-factor along the trigonal axis is very large (62.7). We clarified in this work that the large anisotropy of effective g-factor gives rise to the large spin conversion anisotropy in Bi from experimental and theoretical approaches. Spin-torque ferromagnetic resonance was applied to estimate the spin conversion efficiency in rhombohedral (110) Bi to be 17 to 27%, which is unlike the negligibly small efficiency in Bi(111). Harmonic Hall measurements support the large spin conversion efficiency in Bi(110). A large spin conversion anisotropy as the clear manifestation of the anisotropy of the effective g-factor is observed. Beyond the emblematic case of Bi, our study unveiled the significance of the effective g-factor anisotropy in condensed-matter physics and can pave a pathway toward establishing novel spin physics under g-factor control.

DOI： 10.1073/pnas.2215030120

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

The tunnelling electric current passing through a magnetic tunnel junction (MTJ) is strongly dependent on the relative orientation of magnetizations in ferromagnetic electrodes sandwiching an insulating barrier, rendering efficient readout of spintronics devices^1–5. Thus, tunnelling magnetoresistance (TMR) is considered to be proportional to spin polarization at the interface¹ and, to date, has been studied primarily in ferromagnets. Here we report observation of TMR in an all-antiferromagnetic tunnel junction consisting of Mn₃Sn/MgO/Mn₃Sn (ref. ⁶). We measured a TMR ratio of around 2% at room temperature, which arises between the parallel and antiparallel configurations of the cluster magnetic octupoles in the chiral antiferromagnetic state. Moreover, we carried out measurements using a Fe/MgO/Mn₃Sn MTJ and show that the sign and direction of anisotropic longitudinal spin-polarized current in the antiferromagnet⁷ can be controlled by octupole direction. Strikingly, the TMR ratio (about 2%) of the all-antiferromagnetic MTJ is much larger than that estimated using the observed spin polarization. Theoretically, we found that the chiral antiferromagnetic MTJ may produce a substantially large TMR ratio as a result of the time-reversal, symmetry-breaking polarization characteristic of cluster magnetic octupoles. Our work lays the foundation for the development of ultrafast and efficient spintronic devices using antiferromagnets^8–10.

DOI： 10.1038/s41586-022-05463-w

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Other Link： https://www.nature.com/articles/s41586-022-05463-w

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Physical Society of Japan  

We performed point-contact spectroscopy on CeB6, a heavy fermion compound, using superconducting Nb as a probe tip to achieve high-precision measurements. The differential conductance spectrum represents a sharp zero-bias conductance peak (ZBCP) below T ∼ 6 K. The temperature dependence of the spectra reveals that the ZBCP intensity increases logarithmically with decreasing temperature, owing to the evolution of Kondo resonance. A double-peak structure reflecting the indirect hybridization gap was not observed, suggesting that the development of Kondo lattice coherence is prevented by the emergence of antiferroquadrupolar and=or antiferromagnetic orderings.

DOI： 10.7566/JPSJ.91.113705

Web of Science

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Electrical control of a magnetic state of matter lays the foundation for information technologies and for understanding of spintronic phenomena. Spin–orbit torque provides an efficient mechanism for the electrical manipulation of magnetic orders1–11. In particular, spin–orbit torque switching of perpendicular magnetization in nanoscale ferromagnetic bits has enabled the development of stable, reliable and low-power memories and computation12–14. Likewise, for antiferromagnetic spintronics, electrical bidirectional switching of an antiferromagnetic order in a perpendicular geometry may have huge impacts, given its potential advantage for high-density integration and ultrafast operation15,16. Here we report the experimental realization of perpendicular and full spin–orbit torque switching of an antiferromagnetic binary state. We use the chiral antiferromagnet Mn3Sn (ref. 17), which exhibits the magnetization-free anomalous Hall effect owing to a ferroic order of a cluster magnetic octupole hosted in its chiral antiferromagnetic state18. We fabricate heavy-metal/Mn3Sn heterostructures by molecular beam epitaxy and introduce perpendicular magnetic anisotropy of the octupole using an epitaxial in-plane tensile strain. By using the anomalous Hall effect as the readout, we demonstrate 100 per cent switching of the perpendicular octupole polarization in a 30-nanometre-thick Mn3Sn film with a small critical current density of less than 15 megaamperes per square centimetre. Our theory reveals that the perpendicular geometry between the polarization directions of current-induced spin accumulation and of the octupole persistently maximizes the spin–orbit torque efficiency during the deterministic bidirectional switching process. Our work provides a significant basis for antiferromagnetic spintronics.

DOI： 10.1038/s41586-022-04864-1

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Other Link： https://www.nature.com/articles/s41586-022-04864-1

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

Chirality-induced current-perpendicular-to-plane magnetoresistance (CPP-MR) originates from current-induced spin polarization in molecules. The current-induced spin polarization is widely recognized as a fundamental principle of chiral-induced spin selectivity (CISS). In this study, we investigate chirality-induced current-in-plane magnetoresistance (CIP-MR) in a chiral molecule/ferromagnetic metal bilayer at room temperature. In contrast to CPP-MR, CIP-MR observed in the present study requires no bias charge current through the molecule. The temperature dependence of CIP-MR suggests that thermally driven spontaneous spin polarization in chiral molecules is the key to the observed MR. The novel MR is consistent with recent CISS-related studies, that is, chiral molecules in contact with a metallic surface possess a finite spin polarization.

DOI： 10.1021/jacs.2c00496

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Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.104.L140406

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.104.134431

Language：English   Publishing type：Research paper (scientific journal)  

We performed a point contact spectroscopy study in an intermediate-valence heavy-fermion (HF) compound EuNi2P2. Above the Kondo temperature T-K, the differential conductance spectra show a broad peak due to the Kondo resonance at the Eu site. Below T-K, the broad peak splits into two peaks that can be reproduced by the summation of two Fano curves with the same parameters, indicating the emergence of the indirect hybridization gap in an Anderson lattice. With decreasing temperature, the separation between the two peaks increases and saturates at very low temperatures. The results reveal the evolution of the electronic structure in the HF state due to the development of the lattice coherence.

DOI： 10.1103/physrevb.103.l041113

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.7566/jpscp.30.011022

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.7566/jpscp.30.011139

Language：English   Publishing type：Research paper (scientific journal)  

We performed a point-contact spectroscopy study of intermediate valence compound YbPd, in which two Yb sites are ordered with the valence values of 3+ and 2.6+. Differential conductance spectra exhibit a dip structure at around zero bias with an asymmetric background, which can be reproduced by the summation of two Kondo resonances. Fitting with the Fano equation, the Kondo temperature of the 3+ site is estimated to be similar to 30K, while that of the 2.6+ site is similar to 800K. Additionally, the dip amplitude exhibits -lnT dependence below similar to 25K and saturates at similar to 1K. These results provide direct evidence for the screening of magnetic moments at the valence ordering sites owing to the Kondo effect.

DOI： 10.1103/physrevb.100.245117

Language：Others   Publishing type：Research paper (scientific journal)  

© Published under licence by IOP Publishing Ltd. We report experimental study on low-Temperature hydrogen (H) absorption in vanadium (V) and niobium (Nb) nanocontacts below T = 20 K using a point-contact spectroscopy (PCS) technique. When a small bias voltage is applied between both sides of nanocontacts immersed in liquid H2, the differential conductance (dI/dV) and the second derivative (d2 I/dV 2) are changed from those for pure V and Nb nanocontacts. Further, the spectra approach to those for a high concentrated phase of H with increasing the bias voltage. The results indicate that in-situ investigation of H absorption process from liquid H2 is possible through dI/dV and d2 I/dV 2 measurements using the PCS technique.

DOI： 10.1088/1742-6596/969/1/012008

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1742-6596/897/1/012001

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1742-6596/807/8/082001

Event date： 2023.12

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese  

Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.3

Language：Japanese  

Country：Japan  

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Country：Viet Nam  

Event date： 2022.8

Language：English  

Country：Japan