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論文

Observation of nuclear-spin Seebeck effect

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:16 パーセンタイル:88.21(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$$_3$$ having a large nuclear spin $$(I=5/2)$$ of $$^{55}$$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.

論文

Observation of quantum interference conductance fluctuations in metal rings with strong spin-orbit coupling

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:5.69(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.

論文

Thickness dependence of spin Peltier effect visualized by thermal imaging technique

大門 俊介*; 内田 健一*; 氏家 奈緒美*; 服部 靖之*; 坪井 嶺*; 齊藤 英治

Applied Physics Express, 13(10), p.103001_1 - 103001_4, 2020/10

 被引用回数:6 パーセンタイル:45.15(Physics, Applied)

Magnon propagation length in a ferrimagnetic insulator yttrium iron garnet (YIG) has been investigated by measuring and analyzing the YIG-thickness $$t_mathrm{YIG}$$ dependence of the spin Peltier effect (SPE) in a Pt/YIG junction system. By means of the lock-in thermography technique, we measured the spatial distribution of the SPE-induced temperature modulation in the Pt/YIG system with the $$t_mathrm{YIG}$$ gradation, allowing us to obtain the accurate $$t_mathrm{YIG}$$ dependence of SPE with high $$t_mathrm{YIG}$$ resolution. Based on the $$t_mathrm{YIG}$$ dependence of SPE, we verified the applicability of several phenomenological models to estimate the magnon diffusion length in YIG.

論文

Magnon polarons in the spin Peltier effect

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:18 パーセンタイル:78.55(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 Lu$$_2$$Bi$$_1$$Fe$$_4$$Ga$$_1$$O$$_{12}$$ (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.

論文

Spin transport in insulators without exchange stiffness

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:33 パーセンタイル:88.92(Multidisciplinary Sciences)

The discovery of new materials that efficiently transmit spin currents has been important for spintronics and material science. The electric insulator Gd$$_3$$Ga$$_5$$O$$_{12}$$ (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 $$gg$$ T$$_g$$=180 mK, the magnetic glass-like transition temperature of GGG. At 5 K and 3.5 T, we find a spin diffusion length $$lambda_mathrm{GGG}=1.8pm0.2$$ $$mu$$m and a spin conductivity $$sigma_mathrm{GGG}=(7.3 pm 0.3)times 10^4$$ Sm$$^{-1}$$ that is larger than that of the record quality magnet Y$$_3$$Fe$$_5$$O$$_{12}$$ (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.

論文

Microscopic formulation of nonlinear spin current induced by spin pumping

亀田 麻衣*; 廣部 大地*; 大門 俊介*; 塩見 雄毅*; 高橋 三郎*; 齊藤 英治

Journal of Magnetism and Magnetic Materials, 476, p.459 - 463, 2019/04

 被引用回数:1 パーセンタイル:4.85(Materials Science, Multidisciplinary)

Nonlinear effects of spin pumping have been investigated by numerically calculating the temporal evolution of the magnon number affected by three- and four-magnon interactions. We showed that the three-magnon interaction gives rise to the enhancement of spin-pumping spin current. We also found that the four-magnon interaction in combination with the three-magnon interaction can be responsible for the experimentally observed low-frequency oscillation of spin current.

論文

Magnetomechanical sensing based on delta-E effect in Y$$_3$$Fe$$_5$$O$$_{12}$$ micro bridge

有沢 洋希*; 大門 俊介*; 追川 康之*; Seo, Y.-J.*; 針井 一哉; 大柳 洸一*; 齊藤 英治

Applied Physics Letters, 114(12), p.122402_1 - 122402_5, 2019/03

 被引用回数:4 パーセンタイル:22.27(Physics, Applied)

We have investigated magnetic field effects on mechanical vibration of a magnetic microbridge made of ferrimagnetic insulator Y$$_3$$Fe$$_5$$O$$_{12}$$ at room temperature. The mechanical resonance frequency of the bridge exhibits a steep change at the saturation magnetic field of the microbridge. The steep change was shown to originate from magnetoelastic coupling combined with shape magnetic anisotropy. The competition between shape magnetic anisotropy and the external magnetic field can drive a delta-E effect, the modulation of Young modulus via the magnetoelastic coupling, in a narrow field range, which results in the observed steep change in the mechanical property.

論文

Observation of anisotropic magneto-Peltier effect in nickel

内田 健一*; 大門 俊介*; 井口 亮*; 齊藤 英治

Nature, 558(7708), p.95 - 99, 2018/06

 被引用回数:56 パーセンタイル:91.16(Multidisciplinary Sciences)

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.

論文

Thermographic measurements of the spin Peltier effect in metal/yttrium-iron-garnet junction systems

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

 被引用回数:34 パーセンタイル:82.44(Materials Science, Multidisciplinary)

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.

論文

Generation of megahertz-band spin currents using nonlinear spin pumping

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

 被引用回数:6 パーセンタイル:29.83(Multidisciplinary Sciences)

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 Y$$_3$$Fe$$_5$$O$$_{12}$$. 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.

論文

Concomitant enhancement of the longitudinal spin Seebeck effect and the thermal conductivity in a Pt/YIG/Pt system at low temperatures

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

 被引用回数:46 パーセンタイル:87.78(Materials Science, Multidisciplinary)

We report a simultaneous measurement of a longitudinal spin Seebeck effect (LSSE) and thermal conductivity in a Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ (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 $$S_mathrm{LSSE} > 10 mu$$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.

論文

Thermal imaging of spin Peltier effect

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

 被引用回数:97 パーセンタイル:95.46(Multidisciplinary Sciences)

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.

論文

Complete suppression of longitudinal spin Seebeck effect by frozen magnetization dynamics in Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$

吉川 貴史*; 内田 健一*; 大門 俊介*; 齊藤 英治

Journal of the Physical Society of Japan, 85(6), p.065003_1 - 065003_2, 2016/06

 被引用回数:11 パーセンタイル:62.77(Physics, Multidisciplinary)

The spin Seebeck effect (SSE) in a Pt-film/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ (YIG)-slab junction system has been investigated at low temperatures and under various magnetic fields in the longitudinal configuration. We found that, by increasing applied magnetic fields, the SSE signal gradually decreases and converges to zero without showing sign reversal. The complete field-induced suppression of the SSE is interpreted in terms of the effect of the Zeeman gap in magnon excitation.

論文

Critical suppression of spin Seebeck effect by magnetic fields

吉川 貴史*; 内田 健一*; 大門 俊介*; Qiu, Z.*; 塩見 雄毅*; 齊藤 英治

Physical Review B, 92(6), p.064413_1 - 064413_9, 2015/08

 被引用回数:150 パーセンタイル:97.21(Materials Science, Multidisciplinary)

The longitudinal spin Seebeck effect (LSSE) in Pt/Y$$_3$$Fe$$_5$$O$$_{12}$$ (YIG) junction systems has been investigated at various magnetic fields and temperatures. We found that the LSSE voltage in a Pt/YIG-slab system is suppressed by applying high magnetic fields and this suppression is critically enhanced at low temperatures. The field-induced suppression of the LSSE in the Pt/YIG-slab system is too large at around room temperature to be explained simply by considering the effect of the Zeeman gap in magnon excitation. This result requires us to introduce a magnon-frequency-dependent mechanism into the scenario of LSSE; low-frequency magnons dominantly contribute to the LSSE. The magnetic field dependence of the LSSE voltage was observed to change by changing the thickness of YIG, suggesting that the thermospin conversion by the low-frequency magnons is suppressed in thin YIG films due to the long characteristic lengths of such magnons.

論文

Intrinsic surface magnetic anisotropy in Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ as the origin of low-magnetic-field behavior of the spin Seebeck effect

内田 健一*; 大江 純一郎*; 吉川 貴史*; 大門 俊介*; Hou, D.*; Qiu, Z.*; 齊藤 英治

Physical Review B, 92(1), p.014415_1 - 014415_8, 2015/07

 被引用回数:33 パーセンタイル:78.69(Materials Science, Multidisciplinary)

The magnetic-field dependence of the longitudinal spin Seebeck effect (LSSE) in a Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ (YIG)-slab junction system was found to deviate from a bulk magnetization curve of the YIG slab in a low field range. In this paper, we show that the deviation originates from the difference between surface and bulk magnetization processes in the YIG slab and that it appears even when removing possible extrinsic magnetic anisotropy due to surface roughness and replacing the Pt layer with different materials. This result indicates that the anomalous field dependence of the LSSE is due to an intrinsic magnetic property of the YIG surface. Our numerical calculation based on the Landau-Lifshitz-Gilbert equation shows that the deviation between the LSSE and bulk magnetization curves is qualitatively explained by introducing easy-axis perpendicular magnetic anisotropy near the surface of YIG.

論文

Laser micro-processing as a tool for constructing insulator-based magnonic crystal

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

 被引用回数:8 パーセンタイル:38.29(Physics, Applied)

Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ (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.

論文

Sign of inverse spin Hall voltages generated by ferromagnetic resonance and temperature gradients in yttrium iron garnet platinum bilayers

Schreier, M.*; Bauer, G. E. W.*; Vasyuchka, V.*; Flipse, J.*; 内田 健一*; Lotze, J.*; Lauer, V.*; Chumak, A.*; Serga, A.*; 大門 俊介*; et al.

Journal of Physics D; Applied Physics, 48(2), p.025001_1 - 025001_5, 2015/01

 被引用回数:53 パーセンタイル:87.63(Physics, Applied)

We carried out a concerted effort to determine the absolute sign of the inverse spin Hall effect voltage generated by spin currents injected into a normal metal. We focus on yttrium iron garnet (YIG)|platinum bilayers at room temperature, generating spin currents by microwaves and temperature gradients. We find consistent results for different samples and measurement setups that agree with theory. We suggest a right-hand-rule to define a positive spin Hall angle corresponding to the voltage expected for the simple case of scattering of free electrons from repulsive Coulomb charges.

論文

Effect of spin Hall magnetoresistance on spin pumping measurements in insulating magnet/metal systems

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

磁気抵抗効果がある系では、磁化運動による交流起電力が整流されて直流電圧が生じることが知られている。本研究では、磁性絶縁体/金属複合膜で生じるスピンHall磁気抵抗効果が引き起こす整流電圧のスピンポンピングに対する影響を調べた。スピンHall磁気抵抗効果で整流された直流電圧は、薄膜面内の磁場角度変化に対して、スピンポンピングから生じる逆スピンHall起電力とは異なる角度依存性を示すことを理論的に示すと同時に、マイクロ波キャビティを用いた実験において、この電圧の影響は無視できる大きさであることを実証した。

論文

Effect of spin Hall magnetoresistance on spin pumping measurements in insulating magnet/metal systems

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

 被引用回数:20 パーセンタイル:65.37(Physics, Applied)

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.

論文

Separation of longitudinal spin Seebeck effect from anomalous Nernst effect; Determination of origin of transverse thermoelectric voltage in metal/insulator junctions

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

 被引用回数:120 パーセンタイル:96.14(Materials Science, Multidisciplinary)

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/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ samples, the longitudinal spin Seebeck effect is three orders of magnitude greater than the proximity-driven anomalous Nernst effect.

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