Spin and spin current; From fundamentals to recent progress

前川 禎通; 吉川 貴史*; 中堂 博之; 家田 淳一; 齊藤 英治

Journal of Applied Physics, 133(2), p.020902_1 - 020902_24, 2023/01

https://doi.org/10.1063/5.0133335

Along with the progress of spin science and spintronics research, the flow of electron spins, i.e., spin current, has attracted interest. New phenomena and electronic states were explained in succession using the concept of spin current. Moreover, as many of the conventionally known spintronics phenomena became well organized based on spin current, it has rapidly been recognized as an essential concept in a wide range of condensed matter physics. In this article, we focus on recent developments in the physics of spin, spin current, and their related phenomena, where the conversion between spin angular momentum and different forms of angular momentum plays an essential role. Starting with an introduction to spin current, we first discuss the recent progress in spintronic phenomena driven by spin-exchange coupling: spin pumping, topological Hall torque, and emergent inductor. We, then, extend our discussion to the interaction/interconversion of spins with heat, lattice vibrations, and charge current and address recent progress and perspectives on the spin Seebeck and Peltier effects. Next, we review the interaction between mechanical motion and electron/nuclear spins and argue the difference between the Barnett field and rotational Doppler effect. We show that the Barnett effect reveals the angular momentum compensation temperature, at which the net angular momentum is quenched in ferrimagnets.

Triplon current generation in solids

Chen, Y.*; 佐藤 正寛*; Tang, Y.*; 塩見 雄毅*; 大柳 洸一*; 益田 隆嗣*; 南部 雄亮*; 藤田 全基*; 齊藤 英治

Nature Communications (Internet), 12, p.5199_1 - 5199_7, 2021/08

https://doi.org/10.1038/s41467-021-25494-7

A triplon refers to a fictitious particle that carries angular momentum corresponding to the elementary excitation in a broad class of quantum dimerized spin systems. Such systems without magnetic order have long been studied as a testing ground for quantum properties of spins. Although triplons have been found to play a central role in thermal and magnetic properties in dimerized magnets with singlet correlation, a spin angular momentum flow carried by triplons, a triplon current, has not been detected yet. Here we report spin Seebeck effects induced by a triplon current: triplon spin Seebeck effect, using a spin-Peierls system CuGeO. The result shows that the heating-driven triplon transport induces spin current whose sign is positive, opposite to the spin-wave cases in magnets. The triplon spin Seebeck effect persists far below the spin-Peierls transition temperature, being consistent with a theoretical calculation for triplon spin Seebeck effects.

Evaluation of edge domains in giant magnetoresistive junctions

Frost, W.*; 関 剛斎*; 窪田 崇秀*; Ramos, R.*; 齊藤 英治; 高梨 弘毅*; 廣畑 貴文*

Applied Physics Letters, 118(17), p.172405_1 - 172405_5, 2021/04

https://doi.org/10.1063/5.0049315

We demonstrate that the spin-Seebeck effect can be used to estimate the volume of edge domains formed in a giant magnetoresistive (GMR) device. The thermal gradient induced by Joule heating can be harnessed by the addition of a ferromagnetically insulating channel of FeO on the sides of the GMR pillar. This generates a spin wave in FeO, which couples with the free-layer edge magnetization and controls the reversal of the ferromagnetic layers in one direction only, increasing the current density from A/cm to A/cm. By simple assumption, we estimate the effect of the edge domain on magnetization reversal to be by spin-transfer torque.

Magnetic field dependence of the nonlocal spin Seebeck effect in Pt/YIG/Pt systems at low temperatures

大柳 洸一*; 吉川 貴史*; 齊藤 英治

AIP Advances (Internet), 10(1), p.015031_1 - 015031_5, 2020/01

https://doi.org/10.1063/1.5135944

We report the nonlocal spin Seebeck effect (nlSSE) in a lateral configuration of Pt/YFeO(YIG)/Pt systems as a function of the magnetic field (up to 10 T) at various temperatures (3 K 300 K). The nlSSE voltage decreases with increasing B in a linear regime with respect to the input power (the applied charge-current squared ). The reduction of the nlSSE becomes substantial when the Zeeman energy exceeds thermal energy at low temperatures, which can be interpreted as freeze-out of magnons relevant for the nlSSE. Furthermore, we found the nonlinear power dependence of the nlSSE with increasing at low temperatures ( 20 K), at which the B-induced signal reduction became less visible. Our experimental results suggest that in the nonlinear regime, high-energy magnons are overpopulated compared to those expected from the thermal energy. We also estimate the magnon spin diffusion length as functions of and .

Room temperature and low-field resonant enhancement of spin Seebeck effect in partially compensated magnets

Ramos, R.*; 日置 友智*; 橋本 佑介*; 吉川 貴史*; Frey, P.*; Kreil, A. J. E.*; Vasyuchka, V. I.*; Serga, A. A.*; Hillebrands, B.*; 齊藤 英治

Nature Communications (Internet), 10, p.5162_1 - 5162_8, 2019/11

https://doi.org/10.1038/s41467-019-13121-5

Resonant enhancement of spin Seebeck effect (SSE) due to phonons was recently discovered in YFeO (YIG). This effect is explained by hybridization between the magnon and phonon dispersions. However, this effect was observed at low temperatures and high magnetic fields, limiting the scope for applications. Here we report observation of phonon-resonant enhancement of SSE at room temperature and low magnetic field. We observe in LuBiFeGaO an enhancement 700% greater than that in a YIG film and at very low magnetic fields around 10 T, almost one order of magnitude lower than that of YIG. The result can be explained by the change in the magnon dispersion induced by magnetic compensation due to the presence of non-magnetic ion substitutions. Our study provides a way to tune the magnon response in a crystal by chemical doping, with potential applications for spintronic devices.

Spin Seebeck effect in the layered ferromagnetic insulators CrSiTe 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

https://doi.org/10.1103/PhysRevB.100.060402

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.

スピンゼーベック効果を示すPt/YIG薄膜の硬X線光電子分光による界面分析

小畠 雅明; 吉井 賢資; 福田 竜生; 川崎 郁斗; 岡根 哲夫; 針井 一哉; 家田 淳一; 日置 友智*; 齊藤 英治

no journal, , 

熱によりスピン流を生み出すスピンゼーベック効果を示すPt/YFeO(YIG)系に対し、放射光硬X線光電子分光(HAXPES)により特異物性の起源を明らかにすることを試みた。本系は、外部磁場が存在しない状況でもホール効果を発現する(異常ホール効果)。この起源として、YIG中のFeイオンがPt膜に染み出し、磁性を持つ金属間化合物を生成していることが示唆されている。本研究ではHAXPESにより、界面近傍の鉄イオン等の電子状態を測定した。実験はSPring-8の原子力機構ビームラインBL22XUで行った。Fe 1s光電子スペクトルからは、鉄イオンが3+のものと金属的な0価に近い2つの状態が存在することが判明し、このシナリオを支持する結果が得られた。Pt 4fやO 1sスペクトルなども測定しており、詳しい結果は当日報告する。

原子力電池、原子力電池システム

岡安 悟; 針井 一哉; 家田 淳一

not registered

特願 2019-215282  公開特許公報  特許公報

【課題】放射線による劣化が小さく、小型で寿命の長い原子力電池を得る。 【解決手段】この原子力電池1においては、膜厚方向(Z方向)に沿って、基板10の上に強磁性絶縁層20、金属層30が順次形成される。この原子力電池1においては、強磁性絶縁層(強磁性体層)20と金属層30とで熱電変換素子5が構成される。基板10の下側には、放射線を発する線源(熱源)40が接続されている。スピンゼーベック効果による電位差は図中でY軸方向において発生するため、金属層30におけるY軸方向における両端部側にそれぞれ第1電極31、第2電極32が接続される。この原子力電池1における熱電変換素子5(強磁性絶縁層20、金属層30)においては、放射線照射による劣化が発生しにくいため、α線以外の放射線を発する線源40を用いることができる。