那須 三紀*; 谷内 浩*; 平山 尚樹*; 安達 宏法*; 柿澤 優*; 白勢 裕登*; 西山 博道*; 川本 鉄平*; 犬飼 潤治*; 篠原 武尚; et al.
Journal of Power Sources, 530, p.231251_1 - 231251_11, 2022/05
To accelerate the spread use of polymer electrolyte fuel cells (PEFCs), it is essential to increase power density and durability, while reduce costs. We have succeeded in developing an innovative gas diffusion layer (GDL) with gas flow channels (GDLFC) fabricated on a flat separator that enabled both cost reduction and high performance. In this study, neutron radiography was used to observe the distribution of liquid water during power generation. With using our GDLs and interdigitated (comb-shaped) gas flow channels, the distributions of liquid water were quantitatively imaged, influenced by the current density, the relative humidity, the oxygen utilization, and the water repellency of the GDL. The increase in linear velocity of the oxidant gases effectively suppressed the retention of liquid water at the cathode.
内田 健一*; 安立 裕人; 吉川 貴史*; 桐原 明宏*; 石田 真彦*; 萬 伸一*; 前川 禎通; 齊藤 英治*
Proceedings of the IEEE, 104(10), p.1946 - 1973, 2016/10
The spin Seebeck effect (SSE) refers to the generation of a spin current as a result of a temperature gradient in magnetic materials including insulators. The SSE is applicable to thermoelectric generation because the thermally generated spin current can be converted into a charge current via spin-orbit interaction in conductive materials adjacent to the magnets. The insulator-based SSE device exhibits unconventional characteristics potentially useful for thermoelectric applications, such as simple structure, device-design exibility, and convenient scaling capability. In this article, we review recent studies on the SSE from the viewpoint of thermoelectric applications.
Geprgs, 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
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.
Ramos, R.*; 吉川 貴史*; Aguirre, M.*; Lucas, I.*; Anadn, A.*; 小宅 教文*; 内田 健一*; 安立 裕人; 塩見 淳一郎*; Algarabel, P. A.*; et al.
Physical Review B, 92(22), p.220407_1 - 220407_5, 2015/12
Spin Seebeck effects have been investigated in highly crystalline magnetic multilayer films. Voltage as well as power generated by the spin Seebeck effect were found to be significantly enhanced with increasing the number of layers, . This voltage enhancement defies the simple understanding of the spin Seebeck effect and suggests that spin current flowing between the magnetic layers in the thickness direction plays an important role in the multilayer SSE systems and the observed voltage enhancement.
大沼 悠一*; 安立 裕人; 齊藤 英治; 前川 禎通
Physical Review B, 92(22), p.224404_1 - 224404_8, 2015/12
We theoretically demonstrate that in a ferromagnet/paramagnet bilayer, a magnon instability accompanied by a gigahertz microwave emission can be driven simply by means of a temperature bias. Employing many-body theory for investigating the effects of a phonon heat current on the magnon lifetime, we show that the magnon instability occurs upon the suppression of the umklapp scattering at low temperatures, leading to microwave emission. The present finding provides crucial information about the interplay of spin current and heat current.
安立 裕人; 前川 禎通
Handbook of Spintronics, p.1553 - 1576, 2015/09
Recent progress in our understanding of the interplay of spin and heat is reviewed. A special focus is put on the newly discovered member of the thermo-spin phenomenon termed spin Seebeck effect, that enables thermal injection of spin currents from a ferromagnet into attached nonmagnetic metals over macroscopic scale of several millimeters. Theoretical basis to understand the spin Seebeck effect is reviewed, and other thermal spin effects are shortly discussed as well.
安立 裕人; 前川 禎通
Journal of Applied Physics, 117(17), p.17C710_1 - 17C710_4, 2015/05
内田 健一*; 安立 裕人; 菊池 大介*; 伊藤 俊*; Qiu, Z.*; 前川 禎通; 齊藤 英治
Nature Communications (Internet), 6, p.5910_1 - 5910_8, 2015/01
Surface plasmons, free-electron collective oscillations in metallic nanostructures, provide abundant routes to manipulate light; electron interactions that can localize light energy and alter electromagnetic field distributions at subwavelength scales. The research field of plasmonics thus integrates nano-photonics with electronics. In contrast, electronics is also entering a new era of spintronics, where spin currents play a central role in driving devices. However, plasmonics and spin-current physics have so far been developed independently. Here we report the generation of spin currents by surface plasmon resonance. Using Au nanoparticles embedded in Pt/BiYFeO bilayer films, we show that, when the Au nanoparticles fulfill the surface-plasmon-resonance conditions, spin currents are generated across the Pt/BiYFeO interface.
安立 裕人; 前川 禎通
Solid State Communications, 198, p.22 - 25, 2014/11
大沼 悠一*; 安立 裕人; 齊藤 英治; 前川 禎通
Physical Review B, 89(17), p.174417_1 - 174417_10, 2014/05
A linear-response formulation of the dc spin pumping, i.e., a spin injection from a precessing ferromagnet into an adjacent spin sink, is developed in view of describing many-body effects caused by spin fluctuations in the spin sink. It is shown that, when an itinerant ferromagnet near Tc is used as the spin sink, the spin pumping is largely increased owing to the fluctuation enhancement of the spin conductance across the precessing ferromagnet/spin sink inerface. As an example, the enhanced spin pumping from yttrium iron garnet into nickel palladium alloy is analyzed by means of a self-consistent renormalization scheme, and it is predicted that the enhancement can be as large as tenfold.
葛西 伸哉*; 平山 悠介*; 高橋 有紀子*; 三谷 誠司*; 宝野 和博*; 安立 裕人; 家田 淳一; 前川 禎通
Applied Physics Letters, 104(16), p.162410_1 - 162410_4, 2014/04
We study the non-local spin transport in Permalloy/Cu lateral spin valves (LSVs) fabricated on thermally oxidized Si and MgO substrates. While these LSVs show the same magnitude of spin signals, significant substrate dependence of the baseline resistance was observed. The baseline resistance shows much weaker dependence on the inter-electrode distance than that of the spin transport observed in the Cu wires. A simple analysis of voltage-current characteristics in the baseline resistance indicates the observed result can be explained by a combination of the Peltier and Seebeck effects at the injector and detector junctions, suggesting the usage of high thermal conductivity substrate (or under-layer) is effective to reduce the baseline resistance.
吉川 貴史*; 内田 健一*; 大門 俊介*; 塩見 雄毅*; 安立 裕人; Qiu, Z.*; Hou, D.*; Jin, X.-F.*; 前川 禎通; 齊藤 英治
Physical Review B, 88(21), p.214403_1 - 214403_11, 2013/12
The longitudinal spin Seebeck effect and the anomalous Nernst effect are investigated in various metal/insulator junction systems, and the clear separation of the longitudinal spin Seebeck effect from the anomalous Nernst effect induced by static magnetic proximity is demonstrated. It is shown that, in Pt/YFeO samples, the longitudinal spin Seebeck effect is three orders of magnitude greater than the proximity-driven anomalous Nernst effect.
内田 健一*; 安立 裕人; 梶原 瑛祐*; 前川 禎通; 齊藤 英治
Solid State Physics, 64; Recent Advances in Magnetic Insulators; From Spintronics to Microwave Applications, p.1 - 27, 2013/11
A spin wave is a collective motion of magnetic moment in magnetically ordered materials. Although spin waves have been known and investigated for many years, resent research has revealed that the spin wave plays an important role in spintronics as a carrier of spin current, i.e., a flow of spin angular momentum. Such a spin-wave spin current is available in magnetic insulators even in the absence of conduction electrons, thus opens a new route for investigating spintronic phenomena in magnetic insulators. In this article we review recent progress in insulator spintronics.
前川 禎通; 安立 裕人; 内田 健一*; 家田 淳一; 齊藤 英治
Journal of the Physical Society of Japan, 82(10), p.102002_1 - 102002_23, 2013/10
The flow of electron spin, the so-called "spin current", is a key concept in the recent progress in spintronics. When the spin current interacts with the magnetic moment in a ferromagnetic metal, the angular momentum and energy conservations give rise to the spin transfer torque and spin-motive force, respectively. When it is injected into a non-magnetic metal attached to a ferromagnet, the electric current is induced through the spin-charge conversion mechanism (inverse spin Hall effect). The generation and manipulation of the spin current and a variety of novel phenomena given by the spin current, including the spin Seebeck effect and spin-motive force, are discussed.
安立 裕人; 前川 禎通
Journal of the Korean Physical Society, 62(12), p.1753 - 1758, 2013/06
Spin Seebeck effect refers to a thermal spin injection from a ferromagnet into an attached nonmagnetic metal that occurs over macroscopic scale of several millimeters. The spin Seebeck effect is now established as a universal aspect of ferromagnets since it is observed in a variety of materials ranging from a metallic ferromagnet (NiFe) and semiconducting ferromagnet (GaMnAs) to an insulating magnet (YIG). Here we theoretically discuss the phonon-drag contribution to the spin Seebeck effect. The spin Seebeck effect is driven by nonequilibrium phonons that drag the low-lying spin excitations. This scenario explains simultaneously the local nature of the spin Seebeck effect and the signal enhancement at low temperatures.
前川 禎通; 安立 裕人
Journal of the Korean Physical Society, 62(12), p.1985 - 1989, 2013/06
When metals and semiconductors are placed in a temperature gradient, the electric voltage is generated. This mechanism to convert heat into electric energy, the so-called Seebeck effect, has attracted much attention as the mechanism for utilizing wasted heat energy. The Seebeck effect is due to the entropy carried by the electric current so that it may be enhanced by the internal degrees of freedom of electrons, i.e., spin and orbital. Ferromagnetic insulators are good conductors of spin current, i.e., the flow of electron spins. When they are placed in a temperature gradient, generated is the spin voltage, i.e., spin accumulation. Once the spin voltage is converted into the electric voltage by spin Hall effect in attached metal films such as Pt, the electric voltage is obtained from heat. This is called the spin Seebeck effect. Here, we discuss the Seebeck effect and spin Seebeck effect based on the fluctuation-dissipation theorem and introduce a variety of the devices.
安 東秀*; Vasyuchka, V. I.*; 内田 健一*; Chumak, A. V.*; 山口 和也*; 針井 一哉; 大江 純一郎*; Jungfleisch, M. B.*; 梶原 瑛祐*; 安立 裕人; et al.
Nature Materials, 12(6), p.549 - 553, 2013/06
In this paper, we show a magnetically controllable heat flow caused by a spin-wave current. The direction of the flow can be switched by applying a magnetic field. When microwave energy is applied to a region of ferrimagnetic YFeO, an end of the magnet far from this region is found to be heated in a controlled manner and a negative temperature gradient towards it is formed. This is due to unidirectional energy transfer by the excitation of spin-wave modes without time-reversal symmetry and to the conversion of spin waves into heat. The magnetically controlled remote heating we observe is directly applicable to the fabrication of a heat-flow controller.
安立 裕人; 内田 健一*; 齊藤 英治; 前川 禎通
Reports on Progress in Physics, 76(3), p.036501_1 - 036501_20, 2013/03
Ramos, R.*; 吉川 貴史*; 内田 健一*; 安立 裕人; Lucas, I.*; Aguirre, M.*; Algarabel, P.*; Morelln, L.*; 前川 禎通; 齊藤 英治; et al.
Applied Physics Letters, 102(7), p.072413_1 - 072413_5, 2013/02
We report the experimental observation of the spin Seebeck effect in magnetite thin films. The signal observed at temperatures above the Verwey transition is a contribution from both the anomalous Nernst (ANE) and spin Seebeck (SSE) effects. The contribution from the ANE of the FeO layer to the SSE is found to be negligible due to the resistivity difference between FeO and Pt layers. Below the Verwey transition, the SSE is free from the ANE of the ferromagnetic layer and it is also found to dominate over the ANE due to magnetic proximity effect on the Pt layer.
大沼 悠一; 安立 裕人; 齊藤 英治; 前川 禎通
Physical Review B, 87(1), p.014423_1 - 014423_7, 2013/01
We theoretically investigate the spin Seebeck effect (SSE) in antiferromagnets and ferrimagnets, and show that the SSE vanishes in antiferromagnets but survives in ferrimagnets even at the magnetization compensation point despite the absence of its saturation magnetization. The nonvanishing SSE in ferrimagnets stems from two nondegenerate magnons. We demonstrate that the magnitude of the SSE in ferrimagnets is unchanged across the magnetization compensation point.