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吉川 貴史*; 齊藤 英治
Annual Review of Condensed Matter Physics, 14, p.129 - 151, 2023/03
被引用回数：11 パーセンタイル：85.47(Physics, Condensed Matter)The spin Seebeck effect (SSE) refers to the generation of a spin current as a result of a temperature gradient in a magnetic material, which can be detected electrically via the inverse spin Hall effect in a metallic contact. Since the discovery of the SSE in 2008, intensive studies on the SSE have been conducted to elucidate its origin. SSEs appear in a wide range of magnetic materials including ferro-, ferri-, and antiferromagnets and also paramagnets with classical or quantum spin fluctuation. SSE voltage reflects fundamental properties of a magnet, such as elementary excitation, static magnetic order, spin correlation, and spin transport. In this article, we review recent progress on the SSE in various systems, with particular emphasis on its emerging role as a probe of these magnetic properties in solids. We also briefly discuss the recently discovered nuclear SSE.
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
被引用回数：9 パーセンタイル：96.84(Physics, Applied)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.
大柳 洸一*; 高橋 三郎*; 吉川 貴史*; 齊藤 英治
Physical Review B, 107(1), p.014423_1 - 014423_8, 2023/01
被引用回数：7 パーセンタイル：94.87(Materials Science, Multidisciplinary)We have theoretically investigated the spin Seebeck effect (SSE) in a normal metal (NM)/paramagnetic insulator (PI) bilayer system. Through a linear response approach, we calculated the thermal spin pumping from PI to NM and backflow spin current from NM to PI, where the spin-flip scattering via the interfacial exchange coupling between conduction-electron spin in NM and localized spin in PI is taken into account. We found a finite spin current appears at the interface under the difference in the effective temperatures between spins in NM and PI, and its intensity increases by increasing the density of the localized spin S. Our model well reproduces the magnetic-field-induced reduction of the paramagnetic SSE in Pt/Gd
Ga
O
experimentally observed when the Zeeman energy is comparable to the thermal energy, which can be interpreted as the suppression of the interfacial spin-flip scattering. The present finding provides an insight into the mechanism of paramagnetic SSEs and the thermally induced spin-current generation in magnetic materials.
Lee, O.*; 山本 慧; 埋田 真樹; Zollitsch, C. W.*; Elyasi, M.*; 吉川 貴史*; 齊藤 英治; Bauer, G. E. W.*; 紅林 秀和*
Physical Review Letters, 130(4), p.046703_1 - 046703_6, 2023/01
被引用回数：5 パーセンタイル：80.44(Physics, Multidisciplinary)We experimentally and theoretically demonstrate that nonlinear spin-wave interactions suppress the hybrid magnon-photon quasiparticle or "magnon polariton" in microwave spectra of an yttrium iron garnet film detected by an on-chip split-ring resonator. We observe a strong coupling between the Kittel and microwave cavity modes in terms of an avoided crossing as a function of magnetic fields at low microwave input powers, but a complete closing of the gap at high powers. The experimental results are well explained by a theoretical model including the three-magnon decay of the Kittel magnon into spin waves. The gap closure originates from the saturation of the ferromagnetic resonance above the Suhl instability threshold by a coherent back reaction from the spin waves.
大柳 洸一*; Gomez-Perez, J. M.*; Zhang, X.-P.*; 吉川 貴史*; Chen, Y.*; Sagasta, E.*; Chuvilin, A.*; Hueso, L. E.*; Golovach, V. N.*; Sebastian Bergeret, F.*; et al.
Physical Review B, 104(13), p.134428_1 - 134428_14, 2021/10
被引用回数：14 パーセンタイル：77.64(Materials Science, Multidisciplinary)We report the observation of the spin Hall magnetoresistance (SMR) in a paramagnetic insulator. By measuring the transverse resistance in a Pt/GdGaO (GGG) system at low temperatures, paramagnetic SMR is found to appear with an intensity that increases with the magnetic field aligning GGG's spins. The observed effect is well supported by a microscopic SMR theory, which provides the parameters governing the spin transport at the interface. Our findings clarify the mechanism of spin exchange at a Pt/GGG interface, and demonstrate tunable spin-transfer torque through the field-induced magnetization of GGG. In this regard, paramagnetic insulators offer a key property for future spintronic devices.
吉川 貴史*; Reitz, D.*; 伊藤 宏陽*; 巻内 崇彦*; 杉本 宜陽*; 恒川 翔*; 大門 俊介*; 大柳 洸一*; Ramos, R.*; 高橋 三郎*; et al.
Nature Communications (Internet), 12, p.4356_1 - 4356_7, 2021/07
被引用回数：19 パーセンタイル：88.38(Multidisciplinary Sciences)Thermoelectric effects have been applied to power generators and temperature sensors that convert waste heat into electricity. The effects, however, have been limited to electrons to occur, and inevitably disappear at low temperatures due to electronic entropy quenching. Here, we report thermoelectric generation caused by nuclear spins in a solid: nuclear-spin Seebeck effect. The sample is a magnetically ordered material MnCO having a large nuclear spin 
of 
Mn nuclei and strong hyperfine coupling, with a Pt contact. In the system, we observe low-temperature thermoelectric signals down to 100 mK due to nuclear-spin excitation. Our theoretical calculation in which interfacial Korringa process is taken into consideration quantitatively reproduces the results. The nuclear thermoelectric effect demonstrated here offers a way for exploring thermoelectric science and technologies at ultralow temperatures.
Ramos, R.*; 巻内 崇彦*; 吉川 貴史*; 大門 俊介*; 大柳 洸一*; 齊藤 英治
Applied Physics Letters, 117(24), p.242402_1 - 242402_5, 2020/12
被引用回数：1 パーセンタイル：5.55(Physics, Applied)We investigated the magnetotransport properties of mesoscopic platinum nanostructures (wires and rings) with sub-100 nm lateral dimensions at very low temperatures. Despite the strong spin-orbit interaction in platinum, oscillation of the conductance as a function of the external magnetic field due to quantum interference effects was found to appear. The oscillation was decomposed into Aharonov-Bohm periodic oscillations and aperiodic fluctuations of the conductance due to a magnetic flux piercing the loop of the ring and the metal wires forming the nanostructures, respectively. We also investigated the magnetotransport under different bias currents to explore the interplay between electron phase coherence and spin accumulation effects in strong spin-orbit conductors.
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 YFeO also gives direct proof of its ferrimagnetic nature. The experiments agree very well with atomistic simulations of the scattering cross section.
PdSiHirschberger, M.*; 中島 多朗*; Kriener, M.*; 車地 崇*; Spitz, L.*; Gao, S.*; 吉川 明子*; 山崎 裕一*; 佐賀山 基*; 中尾 裕則*; et al.
Physical Review B, 101(22), p.220401_1 - 220401_6, 2020/06
被引用回数：40 パーセンタイル：91.78(Materials Science, Multidisciplinary)For the skyrmion-hosting intermetallic GdPdSi with centrosymmetric hexagonal lattice and triangular net of rare earth sites, we report a thorough investigation of the magnetic phase diagram. Our work reveals a magnetic phase with an isotropic value of the critical field for all orientations, where the magnetic ordering vector 
is depinned from its preferred directions in the basal plane. The bulk nature of the skyrmion lattice and of other magnetic phases was evidenced by specific-heat measurements. Resistivity anisotropy, likely originating from partial gapping of the density of states along in this Ruderman-Kittel-Kasuya-Yoshida magnet, is picked up via the planar Hall effect (PHE). The PHE confirms the single- nature of the magnetic order when the field is in the hexagonal plane, and allows one to detect the preferred directions of . Several scenarios for the depinned phase are discussed on the basis of the data.
Fe
O小畠 雅明; 吉井 賢資; 福田 竜生; 川崎 郁斗; 岡根 哲夫; 山上 浩志; 矢板 毅; 針井 一哉; 家田 淳一; 岡安 悟; et al.
JPS Conference Proceedings (Internet), 30, p.011192_1 - 011192_6, 2020/03
スピンゼーベック効果を示す系として注目されているPt/YFeO(YIG)系に対し、放射光を用いた硬X線光電子分光(HAXPES)により表面及び界面の電子状態測定を行った。本系ではスピンゼーベック効果のほかに特異な性質を示すことが報告されている。例えば、外部磁場が存在しない状況でもホール効果を発現する。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可能性が提案されている。そこでHAXPESの分析深さを利用し、界面近傍の鉄イオン等の電子状態を測定した。Ptの厚みが2nm, 5nm, 8nm, 10nmの試料を測定したところ、2nmと5nmの試料において鉄イオンの分析を行うことができた。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、上記の可能性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。
大柳 洸一*; 吉川 貴史*; 齊藤 英治
AIP Advances (Internet), 10(1), p.015031_1 - 015031_5, 2020/01
被引用回数：15 パーセンタイル：71.02(Nanoscience & Nanotechnology)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 .
八尋 黎明*; 吉川 貴史*; Ramos, R.*; 大柳 洸一*; 日置 友智*; 大門 俊介*; 齊藤 英治
Physical Review B, 101(2), p.024407_1 - 024407_7, 2020/01
被引用回数：19 パーセンタイル：77.9(Materials Science, Multidisciplinary)We report the observation of anomalous peak structures induced by hybridized magnon-phonon excitation (magnon polarons) in the magnetic field dependence of the spin Peltier effect (SPE) in a LuBi
Fe
GaO (BiGa:LuIG) with Pt contact. The SPE peaks coincide with magnetic fields tuned to the threshold of magnonpolaron formation, consistent with the previous observation in the spin Seebeck effect. The enhancement of SPE is attributed to the lifetime increase in spin current caused by magnon-phonon hybridization in BiGa:LuIG.
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
被引用回数：23 パーセンタイル：76.88(Multidisciplinary Sciences)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.
O/Pt/FeO epitaxial trilayers吉川 貴史*; 鈴木 基寛*; Ramos, R.*; Aguirre, M. H.*; 岡林 潤*; 内田 健一*; Lucas, I.*; Anad
n, A.*; 菊池 大介*; Algarabel, P. A.*; et al.
Journal of Applied Physics, 126(14), p.143903_1 - 143903_11, 2019/10
被引用回数：10 パーセンタイル：49.82(Physics, Applied)Induced Pt ferromagnetism in FeO/Pt/FeO epitaxial trilayer films has been investigated by means of X-ray magnetic circular dichroism (XMCD) at the Pt 
-edges at various temperatures from 300 K to 12 K, including the metal-insulator transition temperature of FeO (
K). At all the temperatures, we observed clear XMCD signals due to Pt ferromagnetism, the amplitude of which was determined to be 0.39 
at 300K and 0.52 at 12 K for the sample with the Pt thickness of 
nm. Interestingly, these values are comparable to or even greater than those in Pt/3
-ferromagnetic-metal (Fe, Ni, Co, and Ni
Fe
) junction systems. The results can be interpreted in terms of a possible Fe interdiffusion into the Pt layer and also possible Fe-Pt alloying due to its high-temperature deposition.
大柳 洸一*; 高橋 三郎*; Cornelissen, L. J.*; Shan, J.*; 大門 俊介*; 吉川 貴史*; Bauer, G. E. W.*; Van Wees, B. J.*; 齊藤 英治
Nature Communications (Internet), 10, p.4740_1 - 4740_6, 2019/10
被引用回数：38 パーセンタイル：89.44(Multidisciplinary Sciences)The discovery of new materials that efficiently transmit spin currents has been important for spintronics and material science. The electric insulator GdGaO (GGG), a standard substrate for growing magnetic films, can be a spin current generator, but has never been considered as a superior conduit for spin currents. Here we report spin current propagation in paramagnetic GGG over several microns. Surprisingly, spin transport persists up to temperatures of 100 K 
T
=180 mK, the magnetic glass-like transition temperature of GGG. At 5 K and 3.5 T, we find a spin diffusion length 
m and a spin conductivity 
Sm that is larger than that of the record quality magnet YFeO (YIG). We conclude that exchange stiffness is not required for efficient spin transport, which challenges conventional models and provides new material-design strategies for spintronic devices.
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.
Wang, H.*; Hou, D.*; Qiu, Z.*; 吉川 貴史*; 齊藤 英治; Jin, X.*
Journal of Applied Physics, 122(8), p.083907_1 - 083907_6, 2017/08
被引用回数：3 パーセンタイル：15.1(Physics, Applied)An electric method for measuring magnetic anisotropy in antiferromagnetic insulators (AFIs) is proposed. When a metallic film with strong spin-orbit interactions, e.g., platinum (Pt), is deposited on an AFI, its resistance should be affected by the direction of the AFI N
el vector due to the spin Hall magnetoresistance (SMR). Accordingly, the direction of the AFI Nel vector, which is affected by both the external magnetic field and the magnetic anisotropy, is reflected in resistance of Pt. The magnetic field angle dependence of the resistance of Pt on AFI is calculated by considering the SMR, which indicates that the antiferromagnetic anisotropy can be obtained experimentally by monitoring the Pt resistance in strong magnetic fields. Calculations are performed for realistic systems such as Pt/CrO, Pt/NiO, and Pt/CoO.
FeO via X-ray magnetic circular dichroism吉川 貴史*; 鈴木 基寛*; 岡林 潤*; 内田 健一*; 菊池 大介*; Qiu, Z.*; 齊藤 英治
Physical Review B, 95(21), p.214416_1 - 214416_7, 2017/06
被引用回数：16 パーセンタイル：60.44(Materials Science, Multidisciplinary)Magnetic moments in an ultrathin Pt film on a ferrimagnetic insulator YFeO
(YIG) have been investigated at high magnetic fields and low temperatures by means of X-ray magnetic circular dichroism (XMCD). We observed an XMCD signal due to the magnetic moments in a Pt film at the Pt 
and 
edges. By means of the element-specific magnetometry, we found that the XMCD signal at the Pt edge gradually increases with increasing the magnetic field even when the field is much greater than the saturation field of YIG. Importantly, the observed XMCD intensity was found to be much greater than the intensity expected from the Pauli paramagnetism of Pt when the Pt film is attached to YIG. These results imply the emergence of induced paramagnetic moments in Pt on YIG and explain the characteristics of the unconventional Hall effect in Pt/YIG systems.
O
/Pt]n multilayersRamos, R.*; 吉川 貴史*; Anadn, A.*; Lucas, I.*; 内田 健一*; Algarabel, P. A.*; Morelln, L.*; Aguirre, M. H.*; 齊藤 英治; Ibarra, M. R.*
AIP Advances (Internet), 7(5), p.055915_1 - 055915_7, 2017/05
被引用回数：19 パーセンタイル：65.79(Nanoscience & Nanotechnology)We report temperature dependent measurements of the spin Seebeck effect (SSE) in multilayers formed by repeated growth of a FeO/Pt bilayer junction. The magnitude of the observed enhancement of the SSE, relative to the SSE in the single bilayer, shows a monotonic increase with decreasing the temperature. This result can be understood by an increase of the characteristic length for spin current transport in the system, in qualitative agreement with the recently observed increase in the magnon diffusion length in FeO at lower temperatures. Our result suggests that the thermoelectric performance of the SSE in multilayer structures can be further improved by careful choice of materials with suitable spin transport properties.
Yagmur, A.*; 内田 健一*; 井原 和紀*; 井岡 郁夫; 吉川 貴史*; 小野 円佳*; 遠藤 純一*; 柏木 王明*; 中島 哲也*; 桐原 明宏*; et al.
Applied Physics Letters, 109(24), p.243902_1 - 243902_4, 2016/12
被引用回数：3 パーセンタイル：14.94(Physics, Applied)スピンゼーベック効果(SSE)に基づく熱電素子の
線抵抗性を調べるため、約3
10
Gyの線照射試験を実施した。SSE素子には、Pt/Ni
Zn
Fe
O/GlassとPt/Bi
Y
FeO/GdGaOを用いた。SSE素子の熱電特性,磁気特性、構造は、線照射により影響されないことを確認した。この結果は、SSE素子が厳しい照射環境でさえ熱電素子として適用可能なことを示した。
