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南部 雄亮*; Barker, J.*; 沖野 夕貴*; 吉川 貴史*; 塩見 雄毅*; Enderle, M.*; Weber, T.*; Winn, B.*; Graves-Brook, M.*; Tranquada, J. M.*; et al.
Physical Review Letters, 125(2), p.027201_1 - 027201_6, 2020/07
被引用回数：45 パーセンタイル：94.07(Physics, Multidisciplinary)We measure the mode-resolved direction of the precessional motion of the magnetic order, i.e., magnon polarization, via the chiral term of inelastic polarized neutron scattering spectra. The magnon polarization is a unique and unambiguous signature of magnets and is important in spintronics, affecting thermodynamic properties such as the magnitude and sign of the spin Seebeck effect. However, it has never been directly measured in any material until this work. The observation of both signs of magnon polarization in Y
Fe
O
also gives direct proof of its ferrimagnetic nature. The experiments agree very well with atomistic simulations of the scattering cross section.
and CrGeTe伊東 直洋*; 吉川 貴史*; Barker, J.*; 廣部 大地*; 塩見 雄毅*; 齊藤 英治
Physical Review B, 100(6), p.060402_1 - 060402_6, 2019/08
被引用回数：43 パーセンタイル：88.83(Materials Science, Multidisciplinary)We have studied the longitudinal spin Seebeck effect (LSSE) in the layered ferromagnetic insulators CrSiTe and CrGeTe covered by Pt films in the measurement configuration where spin current traverses the ferromagnetic Cr layers. The LSSE response is clearly observed in the ferromagnetic phase and, in contrast to a standard LSSE magnet YFeO, persists above the critical temperatures in both CrSiTe/Pt and CrGeTe/Pt samples. With the help of a numerical calculation, we attribute the LSSE signals observed in the paramagnetic regime to exchange-dominated interlayer transport of in-plane paramagnetic moments reinforced by short-range ferromagnetic correlations and strong Zeeman effects.
Qiu, Z.*; Hou, D.*; Barker, J.*; 山本 慧; Gomonay, O.*; 齊藤 英治*
Nature Materials, 17(7), p.577 - 580, 2018/05
被引用回数：98 パーセンタイル：95.73(Chemistry, Physical)巨大磁気抵抗とは導体絶縁体相転移の近傍で磁場により電気抵抗が大幅に変化する現象を指す。これは磁気構造と電気伝導の強い相関に由来し、数十年にわたって盛んに研究されてきた。本稿では、反強磁性絶縁体であるCr
O
が室温においてスピン流についての明確な導体不導体を起こすことを報告する。スピン流透過率はネール温度近傍の14度の間で2桁変化する。このスピン流についての導体不導体転移は磁場によって制御可能であり、定温で最大500%透過率が変化し事実上のスピン流透過不透過切り替えのスイッチとなる。
Hou, D.*; Qiu, Z.*; Barker, J.*; 佐藤 浩司*; 山本 慧; V
lez, S.*; Gomez-Perez, J. M.*; Hueso, L. E.*; Casanova, F.*; 齊藤 英治
Physical Review Letters, 118(14), p.147202_1 - 147202_6, 2017/04
被引用回数：109 パーセンタイル：97.22(Physics, Multidisciplinary)Spin Hall magnetoresistance (SMR) has been investigated in Pt/NiO/YIG structures in a wide range of temperature and NiO thickness. The SMR shows a negative sign below a temperature that increases with the NiO thickness. This is contrary to a conventional SMR theory picture applied to the Pt/YIG bilayer, which always predicts a positive SMR. The negative SMR is found to persist even when NiO blocks the spin transmission between Pt and YIG, indicating it is governed by the spin current response of the NiO layer. We explain the negative SMR by the NiO "spin flop" coupled with YIG, which can be overridden at higher temperature by positive SMR contribution from YIG. This highlights the role of magnetic structure in antiferromagnets for transport of pure spin current in multilayers.
Gepr
gs, S.*; Kehlberger, A.*; Coletta, F.*; Qiu, Z.*; Guo, E.-J.*; Schulz, T.*; Mix, C.*; Meyer, S.*; Kamra, A.*; Althammer, M.*; et al.
Nature Communications (Internet), 7, p.10452_1 - 10452_6, 2016/02
被引用回数：152 パーセンタイル：97.33(Multidisciplinary Sciences)Magnons are the elementary excitations of a magnetically ordered system. Here, we show that the spin Seebeck effect is sensitive to the complexities of the magnon spectrum. The spin Seebeck effect is caused by a thermally excited spin dynamics that is converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the spin Seebeck effect in the ferrimagnet gadlinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that high-energy exchange magnons play a key role in the spin Seebeck effect.
