内田 健一*; 大門 俊介*; 井口 亮*; 齊藤 英治
Nature, 558(7708), p.95 - 99, 2018/06
The Peltier effect, discovered in 1834, converts a charge current into a heat current in a conductor, and its performance is described by the Peltier coefficient, which is defined as the ratio of the generated heat current to the applied charge current. To exploit the Peltier effect for thermoelectric cooling or heating, junctions of two conductors with different Peltier coefficients have been believed to be indispensable. Here we challenge this conventional wisdom by demonstrating Peltier cooling and heating in a single material without junctions. This is realized through an anisotropic magneto-Peltier effect in which the Peltier coefficient depends on the angle between the directions of a charge current and magnetization in a ferromagnet. By using active thermography techniques, we observe the temperature change induced by this effect in a plain nickel slab. We find that the thermoelectric properties of the ferromagnet can be redesigned simply by changing the configurations of the charge current and magnetization, for instance, by shaping the ferromagnet so that the current must flow around a curve. Our experimental results demonstrate the suitability of nickel for the anisotropic magneto-Peltier effect and the importance of spin-orbit interaction in its mechanism. The anisotropic magneto-Peltier effect observed here is the missing thermoelectric phenomenon in ferromagnetic materials-the Onsager reciprocal of the anisotropic magneto-Seebeck effect previously observed in ferromagnets and its simplicity might prove useful in developing thermal management technologies for electronic and spintronic devices.
小林 大眞*; 吉川 智英*; 松尾 衛*; 井口 亮*; 前川 禎通; 齊藤 英治; 能崎 幸雄*
Physical Review Letters, 119(7), p.077202_1 - 077202_5, 2017/08
We demonstrate the generation of alternating spin current (SC) via spin-rotation coupling (SRC) using a surface acoustic wave (SAW) in a Cu film. Ferromagnetic resonance caused by injecting SAWs was observed in a Ni-Fe film attached to a Cu film, with the resonance further found to be suppressed through the insertion of a SiO film into the interface. The intensity of the resonance depended on the angle between the wave vector of the SAW and the magnetization of the Ni-Fe film. This angular dependence is explicable in terms of the presence of spin transfer torque from a SC generated via SRC.
大門 俊介*; 内田 健一*; 井口 亮*; 日置 友智*; 齊藤 英治
Physical Review B, 96(2), p.024424_1 - 024424_12, 2017/07
The spin Peltier effect (SPE), heat-current generation due to spin-current injection, in various metal (Pt, W, and Au single layers and Pt/Cu bilayer)/ferrimagnetic insulator [yttrium-iron-garnet (YIG)] junction systems has been investigated by means of a lock-in thermography (LIT) method. The SPE is excited by a spin current across the metal/YIG interface, which is generated by applying a charge current to the metallic layer via the spin Hall effect. The LIT method enables the thermal imaging of the SPE free from the Joule-heating contribution. Importantly, we observed spin-current-induced temperature modulation not only in the Pt/YIG and W/YIG systems, but also in the Au/YIG and Pt/Cu/YIG systems, excluding the possible contamination by anomalous Ettingshausen effects due to proximity-induced ferromagnetism near the metal/YIG interface. As demonstrated in our previous study, the SPE signals are confined only in the vicinity of the metal/YIG interface; we buttress this conclusion by reducing a spatial blur due to thermal diffusion in an infrared-emission layer on the sample surface used for the LIT measurements. We also found that the YIG-thickness dependence of the SPE is similar to that of the spin Seebeck effect measured in the same Pt/YIG sample, implying the reciprocal relation between them.
渡辺 真悟*; 廣部 大地*; 塩見 雄毅*; 井口 亮*; 大門 俊介*; 亀田 麻衣*; 高橋 三郎*; 齊藤 英治
Scientific Reports (Internet), 7, p.4576_1 - 4576_6, 2017/07
Spin pumping enables the generation of d.c. and gigahertz-band (GHz-band) voltages from an applied microwave via magnetization dynamics when combined with inverse spin Hall effects. However, generating such voltages in the in-between frequency region, or the megahertz (MHz) band, has been difficult since ferromagnetic resonance usually occurs in the GHz band. Here we show that in spite of GHz-band microwaves applied, MHz-band voltages can be generated by spin pumping with use of nonlinear magnetization dynamics in YFeO. The mechanism is ascribed to the MHz-band oscillation of the amplitude of the magnetization precession, which is projected onto a rectified voltage component via spin pumping. The present finding could be useful for frequency down-conversion thanks to the simple and durable structure, continuous-wave operation, and the tunability of an output frequency with low magnetic fields.
日置 友智*; 井口 亮*; Qiu, Z.*; Hou, D.*; 内田 健一*; 齊藤 英治
Applied Physics Express, 10(7), p.073002_1 - 073002_4, 2017/06
We have investigated the magnetic-field-induced suppression of the longitudinal spin Seebeck effect (LSSE) by using a time-resolved measurement technique at room temperature. The result manifested two distinctive time domains: the short-time domain where the observed voltage is insensitive to the magnetic fields, and the long-time domain where the both response time and the magnitude of the observed voltage decreased simultaneously by the magnetic fields. We estimated the magnon propagation length by fitting the transient LSSE response. The propagation length shows a strong dependence on the applied magnetic field, indicating the importance of long-range and low-frequency magnons in the LSSE.
井口 亮*; 内田 健一*; 大門 俊介*; 齊藤 英治
Physical Review B, 95(17), p.174401_1 - 174401_7, 2017/05
We report a simultaneous measurement of a longitudinal spin Seebeck effect (LSSE) and thermal conductivity in a Pt/YFeO (YIG)/Pt system in a temperature range from 10 to 300 K. By directly monitoring the temperature difference in the system, we excluded thermal artifacts in the LSSE measurements. It is found that both the LSSE signal and the thermal conductivity of YIG exhibit sharp peaks at the same temperature, different from previous reports. The maximum LSSE coefficient is found to be V/K, one-order-of magnitude greater than the previously reported values. The concomitant enhancement of the LSSE and thermal conductivity of YIG suggests the strong correlation between magnon and phonon transport in the LSSE.
井口 亮*; 齊藤 英治
Journal of the Physical Society of Japan, 86(1), p.011003_1 - 011003_13, 2017/01
Conversions between spin and charge currents are core technologies in recent spintronics. In this article, we provide methods for estimating inverse spin Hall effects (ISHEs) induced by using microwave-driven spin pumping (SP) as a spin-current generator. ISHE and SP induce an electromotive force at the ferromagnetic or spin-wave resonance, which offers a valuable electric method of studying spin physics in materials. At the resonance, a microwave for exciting the magnetization dynamics induces an additional electromotive force via rf-current rectification and thermoelectric effects. We discuss methods of separating the signals generated from such extrinsic microwave effects by controlling sample structures and configurations. These methods are helpful in performing accurate measurements on ISHE induced by SP, enabling quantitative studies on the conversion between spin and charge currents on various kinds of materials.
廣部 大地*; 佐藤 正寛*; 川股 隆行*; 塩見 雄毅*; 内田 健一*; 井口 亮*; 小池 洋二*; 前川 禎通; 齊藤 英治
Nature Physics, 13(1), p.30 - 34, 2017/01
Quantum spin fluctuation in a low-dimensional or frustrated magnet breaks magnetic ordering while keeping spin correlation. Such fluctuation has been a central topic in magnetism because of its relevance to high-Tc superconductivity and topological states. However, utilizing such spin states has been quite difficult. In a one-dimensional spin-1/2 chain, a particle-like excitation called a spinon is known to be responsible for spin fluctuation in a paramagnetic state. Spinons behave as a Tomonaga-Luttinger liquid at low energy, and the spin system is often called a quantum spin chain. Here we show that a quantum spin chain generates and carries spin current, which is attributed to spinon spin current. This is demonstrated by observing an anisotropic negative spin Seebeck effect along the spin chains in SrCuO. The results show that spin current can flow even in an atomic channel owing to long-range spin fluctuation.
大門 俊介*; 井口 亮*; 日置 友智*; 齊藤 英治; 内田 健一*
Nature Communications (Internet), 7, p.13754_1 - 13754_7, 2016/12
The Peltier effect modulates the temperature of a junction comprising two different conductors in response to charge currents across the junction, which is used in solid-state heat pumps and temperature controllers in electronics. Recently, in spintronics, a spin counterpart of the Peltier effect was observed. The "spin Peltier effect" modulates the temperature of a magnetic junction in response to spin currents. Here we report thermal imaging of the spin Peltier effect; using active thermography technique, we visualize the temperature modulation induced by spin currents injected into a magnetic insulator from an adjacent metal. The thermal images reveal characteristic distribution of spin-current-induced heat sources, resulting in the temperature change confined only in the vicinity of themetal/insulator interface. This finding allows us to estimate the actual magnitude of the temperature modulation induced by the spin Peltier effect, which is more than one order of magnitude greater than previously believed.
Hou, D.*; Qiu, Z.*; 井口 亮*; 佐藤 浩司*; Vehstedt, E. K.*; 内田 健一*; Bauer, G. E. W.*; 齊藤 英治
Nature Communications (Internet), 7, p.12265_1 - 12265_6, 2016/07
Applying magnetic fields has been the method of choice to magnetize non-magnetic materials, but they are difficult to focus. The magneto-electric effect and voltage-induced magnetization generate magnetization by applied electric fields, but only in special compounds or heterostructures. Here we demonstrate that a simple metal such as gold can be magnetized by a temperature gradient or magnetic resonance when in contact with a magnetic insulator by observing an anomalous Hall-like effect, which directly proves the breakdown of time-reversal symmetry. Such Hall measurements give experimental access to the spectral spin Hall conductance of the host metal, which is closely related to other spin caloritronics phenomena such as the spin Nernst effect and serves as a reference for theoretical calculation.
Yagmur, A.*; 軽部 修太郎*; 内田 健一*; 近藤 浩太*; 井口 亮*; 吉川 貴史*; 大谷 義近*; 齊藤 英治
Applied Physics Letters, 108(24), p.242409_1 - 242409_4, 2016/06
The longitudinal spin Seebeck effect (SSE) in Bi O/Cu/yttrium-iron-garnet (YIG) devices has been investigated. When an out-of-plane temperature gradient is applied to the BiO/Cu/YIG device, a spin current is generated across the Cu/YIG interface via the SSE and then converted into electric voltage due to the spinO/Cu interface. The sign of the SSE voltage in the BiO/Cu/YIG devices is opposite to that induced by the conventional inverse spin Hall effect in Pt/YIG devices. The SSE voltage in the BiO/Cu/YIG devices disappears in the absence of the BiOlayer and its thermoelectric conversion efficiency is independent of the Cu thickness, indicating the important role of the BiO/Cu interface. This result demonstrates that not only the bulk inverse spin Hall effect but also the spin-orbit coupling near the interface can be used for SSE-based thermoelectric generation.
Haidar, S. M.*; 井口 亮*; Yagmur, A.*; Lustikova, J.*; 塩見 雄毅*; 齊藤 英治
Journal of Applied Physics, 117(18), p.183906_1 - 183906_6, 2015/05
We have investigated dc voltage generation induced by ferromagnetic resonance in a CoFe/Pt film. In order to reduce rectification effects of anisotropic magnetoresistance and the planar Hall effect, which may be observed simultaneously with the inverse spin Hall effect, we selected CoFe with extremely small anisotropic magnetoresistance as a spin injector. Using the difference in the spectral shape of voltage and in the angle dependence of in-plane magnetization among the effects, we demonstrated that the generated dc voltage is governed by the inverse spin Hall effect induced by spin pumping.
大門 俊介*; 井口 亮*; 内田 健一*; 齊藤 英治
Journal of Physics D; Applied Physics, 48(16), p.164014_1 - 164014_4, 2015/04
YFeO (YIG) films with a periodic-antidot-array structure fabricated by laser microprocessing is shown to exhibit clear characteristics of two-dimensional (2D) magnonic crystals. The experimental results demonstrate that the spin-wave-resonance spectra in the YIG films are modulated by the periodic antidot structure. The frequency and lattice constant dependences of the spectra are well reproduced by a numerical calculation based on magnonic band structures of the 2D magnonic crystals. Since the laser micro-processing is compatible with various thin-film fabrication methods, it can be a powerful tool for constructing magnonic crystals.
内田 健一*; Qiu, Z.*; 吉川 貴史*; 井口 亮*; 齊藤 英治
Applied Physics Letters, 106(5), p.052405_1 - 052405_5, 2015/02
The temperature dependence of spin Hall magnetoresistance (SMR) in Pt/YFeO (YIG) bilayer films has been investigated in a high temperature range from room temperature to near the Curie temperature of YIG. The experimental results show that the magnitude of the magnetoresistance ratio induced by the SMR monotonically decreases with increasing the temperature and almost disappears near the Curie temperature. We found that, near the Curie temperature, the temperature dependence of the SMR in the Pt/YIG film is steeper than that of a magnetization curve of the YIG; the critical exponent of the magnetoresistance ratio is estimated to be 0.9. This critical behavior of the SMR is attributed mainly to the temperature dependence of the spin-mixing conductance at the Pt/YIG interface.
Lustikova, J.*; 塩見 雄毅*; Qiu, Z.*; 吉川 貴史*; 井口 亮*; 内田 健一*; 齊藤 英治
Journal of Applied Physics, 116(15), p.153902_1 - 053902_6, 2014/10
Spin current injection from sputtered yttrium iron garnet (YIG) films into an adjacent platinum layer has been investigated by means of the spin pumping and the spin Seebeck effects. Films witha thickness of 83 and 96 nanometers were fabricated by on-axis magnetron rf sputtering at room temperature and subsequent post-annealing. From the frequency dependence of the ferromagneticresonance linewidth, the damping constant has been estimated to be (7.01.0) 10. Magnitudes of the spin current generated by the spin pumping and the spin Seebeck effect are ofthe same order as values for YIG films prepared by liquid phase epitaxy. The efficient spin current injection can be ascribed to a good YIG/Pt interface, which is confirmed by the large spin-mixingconductance (2.0 0.2) 10 m.
井口 亮*; 佐藤 浩司*; 廣部 大地*; 大門 俊介*; 齊藤 英治
Applied Physics Express, 7(1), p.013003_1 - 013003_4, 2014/01
井口 亮*; 佐藤 浩司*; 廣部 大地*; 大門 俊介*; 齊藤 英治
Applied Physics Express, 7(1), p.013003_1 - 013003_4, 2014/01
We investigate a dc rectification effect of magnetization dynamics based on spin Hall magnetoresistance (SMR) in an insulating magnet/metal system on spin pumping measurements. We theoretically find that the rectification effect by SMR has different in-plane magnetization angle dependence from that of the inverse spin Hall effect on the spin pumping. The negligible contribution from the rectification effect is experimentally confirmed in a cavity measurement.
井口 亮*; 安藤 和也*; Qiu, Z.*; 安 東秀*; 齊藤 英治; 佐藤 徹哉*
Applied Physics Letters, 102(2), p.022406_1 - 022406_3, 2013/01
石田 真彦*; 追川 康之*; 井口 亮*; 齊藤 英治*; 澤田 亮人*; 桐原 明宏*
石田 真彦*; 追川 康之*; 井口 亮*; 齊藤 英治*; 澤田 亮人*; 桐原 明宏*