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論文

Tolerance of spin-Seebeck thermoelectricity against irradiation by swift heavy ions

岡安 悟; 針井 一哉*; 小畠 雅明; 吉井 賢資; 福田 竜生; 石田 真彦*; 家田 淳一; 齊藤 英治

Journal of Applied Physics, 128(8), p.083902_1 - 083902_7, 2020/08

The ion-irradiation tolerance of thermoelectric devices based on the spin Seebeck effect (SSE) was investigated by using 320 MeV gold ion (Au$$^{24+}$$) beams modeling cumulative damages due to fission products emitted from the surface of spent nuclear fuels. For this purpose, prototypical Pt/Y$$_3$$Fe$$_5$$O$$_{12}$$/Gd$$_3$$Ga$$_5$$O$$_{12}$$ SSE elements were irradiated with varying the dose level at room temperature and measured the SSE voltage of them. We confirmed that the thermoelectric and magnetic properties of the SSE elements are not affected by the ion-irradiation up to $$10^{10}$$ ions/cm$$^2$$ fluence and that the SSE signal is extinguished around $$10^{12}$$ ions/cm$$^2$$, in which the ion tracks almost fully cover the sample surface. We also performed the hard X-ray photoemission spectroscopy (HAXPES) measurements to understand the effects at the interface of Pt/Y$$_3$$Fe$$_5$$O$$_{12}$$. The HAXPES measurements suggest that the chemical reaction that diminishes the SSE signals is enhanced with the increase of the irradiation dose. The present study demonstrates that SSE-based devices are applicable to thermoelectric generation even in harsh environments for a long time period.

論文

Giant spin hydrodynamic generation in laminar flow

高橋 遼*; 中堂 博之; 松尾 衛; 針井 一哉*; 大沼 悠一*; 前川 禎通; 齊藤 英治

Nature Communications (Internet), 11, p.3009_1 - 3009_6, 2020/06

 被引用回数:0 パーセンタイル:100(Multidisciplinary Sciences)

Hydrodynamic motion can generate a flux of electron-spin's angular momentum via the coupling between fluid rotation and electron spins. Such hydrodynamic generation, called spin hydrodynamic generation (SHDG), has recently attracted attention in a wide range of fields, especially in spintronics. Spintronics deals with spin-mediated interconversion taking place on a micro or nano scale because of the spin-diffusion length scale. To be fully incorporated into the interconversion, SHDG physics should also be established in such a minute scale, where most fluids exhibit a laminar flow. Here, we report electric voltage generation due to the SHDG in a laminar flow of a liquid-metal mercury. The experimental results show a scaling rule unique to the laminar-flow SHDG. Furthermore, its energy con- version efficiency turns out to be about 105 greater than of the turbulent one. Our findings reveal that the laminar-flow SHDG is suitable to downsizing and to extend the coverage of fluid spintronics.

論文

Hard X-ray photoelectron spectroscopy study of Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$

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/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$(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$$^{3+}$$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。

論文

Spin Seebeck mechanical force

針井 一哉; Seo, Y.-J.*; 堤 康雅*; 中堂 博之; 大柳 洸一*; 松尾 衛; 塩見 雄毅*; 小野 崇人*; 前川 禎通; 齊藤 英治

Nature Communications (Internet), 10(1), p.2616_1 - 2616_5, 2019/06

 被引用回数:8 パーセンタイル:11.64(Multidisciplinary Sciences)

Electric current has been used to send electricity to far distant places. On the other hand, spin current, a flow of electron spin, can in principle also send angular momentum to distant places. In a magnet, there is a universal spin carrier called a spin wave, a wave-type excitation of magnetization. Since spin waves exhibit a long propagation length, it should be able to send angular momentum that can generate torque and force at a distant place: a new function of magnets. Here we observe mechanical angular momentum transmission and force generation due to spin waves injected into Y$$_3$$Fe$$_5$$O$$_{12}$$ by the spin-Seebeck effect. The spin-wave current, transmitted through a Y$$_3$$Fe$$_5$$O$$_{12}$$ micro cantilever, was found to create a mechanical force on the cantilever as a non-local reaction of the spin-Seebeck effect. Spin-wave current can be generated remotely even in open circuits, and it can be used to drive micro mechanical devices.

論文

Angular momentum compensation manipulation to room temperature of the ferrimagnet Ho$$_{3-x}$$Dy$$_{x}$$Fe$$_5$$O$$_{12}$$ detected by the Barnett effect

今井 正樹; 中堂 博之; 小野 正雄; 針井 一哉; 松尾 衛; 大沼 悠一*; 前川 禎通; 齊藤 英治

Applied Physics Letters, 114(16), p.162402_1 - 162402_4, 2019/04

 被引用回数:6 パーセンタイル:17.09(Physics, Applied)

We demonstrate that the angular momentum compensation temperature $$T_{rm A}$$, at which the net angular momentum in the sample disappears, can be controlled in Ho$$_3$$Fe$$_5$$O$$_{12}$$ by partially substituting Dy for Ho. The $$T_{rm A}$$ can be detected using the Barnett effect, by which mechanical rotation magnetizes an object due to spin-rotation coupling. We found that $$T_{rm A}$$ increases with the Dy content and clarified that the $$T_{rm A}$$ of Ho$$_{1.5}$$Dy$$_{1.5}$$Fe$$_5$$O$$_{12}$$ coincides with room temperature. The Barnett effect enables us to explore materials applicable to magnetic devices utilizing the angular momentum compensation only by rotating the powder sample at room temperature.

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:2 パーセンタイル:50.59(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 gyromagnetic reversal

今井 正樹; 緒方 裕大*; 中堂 博之; 小野 正雄; 針井 一哉; 松尾 衛*; 大沼 悠一*; 前川 禎通; 齊藤 英治

Applied Physics Letters, 113(5), p.052402_1 - 052402_3, 2018/07

 被引用回数:7 パーセンタイル:33.3(Physics, Applied)

We report direct observation of gyromagnetic reversal, which is the sign change of gyromagnetic ratio in a ferrimagnet Ho$$_3$$Fe$$_5$$O$$_{12}$$, by using the Barnett effect measurement technique at low temperatures. The Barnett effect is a phenomenon in which magnetization is induced by mechanical rotation through the coupling between rotation and total angular momentum $$J$$ of electrons. The magnetization of Ho$$_3$$Fe$$_5$$O$$_{12}$$ induced by mechanical rotation disappears at 135 K and 240 K. The temperatures correspond to the magnetization compensation temperature $$T_{rm M}$$ and the angular momentum compensation temperature $$T_{rm A}$$, respectively. Between $$T_{rm M}$$ and $$T_{rm A}$$, the magnetization flips over to be parallel against the angular momentum due to the sign change of gyromagnetic ratio. This study provides an unprecedented technique to explore the gyromagnetic properties.

論文

Enhanced orbital magnetic moment in FeCo nanogranules observed by Barnett effect

緒方 裕大; 中堂 博之; Gu, B.; 小林 伸聖*; 小野 正雄; 針井 一哉; 松尾 衛; 齊藤 英治; 前川 禎通

Journal of Magnetism and Magnetic Materials, 442, p.329 - 331, 2017/11

 被引用回数:4 パーセンタイル:52.83(Materials Science, Multidisciplinary)

The gyroscopic g factor, $$g'$$, of FeCo nanogranules embedded in a matrix of MgF$$_2$$ (FeCo-MgF$$_2$$) was determined by measuring the magnetic-field generation from a rotating sample due to the Barnett effect. The $$g'$$ value of the FeCo-MgF$$_2$$ is estimated to be 1.76 $$pm$$ 0.11. The orbital contribution to the magnetic moment in the FeCo nanogranules was found to be quite large compared with that in bulk FeCo, being consistent with a density-functional-theory calculation that shows that the orbital magnetic moment may increase at the FeCo/MgF$$_2$$ interfaces. The result suggests that the orbital magnetic moment is enhanced by symmetry breaking at the surface of the FeCo nanogranules.

論文

Fabrication and magnetic control of Y$$_3$$Fe$$_5$$O$$_{12}$$ cantilevers

Seo, Y.-J.*; 針井 一哉; 高橋 遼*; 中堂 博之; 大柳 洸一*; Qiu, Z.*; 小野 崇人*; 塩見 雄毅*; 齊藤 英治

Applied Physics Letters, 110(13), p.132409_1 - 132409_4, 2017/03

 被引用回数:11 パーセンタイル:29.06(Physics, Applied)

フェリ磁性体であるY$$_3$$Fe$$_5$$O$$_{12}$$を用いたサブミクロンカンチレバーを収束イオンビーム法によって作成し、その振動特性を磁場によって制御した。カンチレバーは縦横2つの振動モードを示し、それぞれのモードは外部磁場の印加によって共鳴周波数が減少、増大した。この結果は磁気力の磁場変化を取り扱った数値シミュレーションでよく再現された。周波数変化は数%に及ぶことから、磁場による高効率な振動制御が行われたと結論できる。

論文

Gyroscopic $$g$$ factor of rare earth metals

緒方 裕大; 中堂 博之; 小野 正雄; 針井 一哉; 松尾 衛; 前川 禎通; 齊藤 英治

Applied Physics Letters, 110(7), p.072409_1 - 072409_4, 2017/02

 被引用回数:9 パーセンタイル:35.46(Physics, Applied)

We develop the $$in$$ $$situ$$ magnetization measurement apparatus for observing the Barnett effect consisting of a fluxgate sensor, high speed rotor with frequencies of up to 1.5 kHz, and magnetic shield at room temperature. The effective magnetic field (Barnett field) in a sample arising from rotation magnetizes the sample and is proportional to the rotational frequency. The gyroscopic $$g$$ factor, $$g'$$, of rare earth metals, in particular, Gd, Tb and Dy were estimated to be 2.00$$pm$$0.08, 1.53$$pm$$0.17, and 1.15$$pm$$0.32, respectively, from the slopes of the rotation dependence of the Barnett field. This study provides a technique to determine the $$g'$$ factor even in samples where the spectroscopic method may not be available.

論文

Spin hydrodynamic generation

高橋 遼*; 松尾 衛; 小野 正雄; 針井 一哉; 中堂 博之; 岡安 悟; 家田 淳一; 高橋 三郎*; 前川 禎通; 齊藤 英治

Nature Physics, 12, p.52 - 56, 2016/01

 被引用回数:41 パーセンタイル:6.49(Physics, Multidisciplinary)

Magnetohydrodynamic generation is the conversion of fluid kinetic energy into electricity. Such conversion, which has been applied to various types of electric power generation, is driven by the Lorentz force acting on charged particles and thus a magnetic field is necessary. On the other hand, recent studies of spintronics have revealed the similarity between the function of a magnetic field and that of spin-orbit interactions in condensed matter. This suggests the existence of an undiscovered route to realize the conversion of fluid dynamics into electricity without using magnetic fields. Here we show electric voltage generation from fluid dynamics free from magnetic fields; we excited liquid-metal flows in a narrow channel and observed longitudinal voltage generation in the liquid. This voltage has nothing to do with electrification or thermoelectric effects, but turned out to follow a universal scaling rule based on a spin-mediated scenario. The result shows that the observed voltage is caused by spin-current generation from a fluid motion: spin hydrodynamic generation. The observed phenomenon allows us to make mechanical spin-current and electric generators, opening a door to fluid spintronics.

論文

Barnett effect in paramagnetic states

小野 正雄; 中堂 博之; 針井 一哉; 岡安 悟; 松尾 衛; 家田 淳一; 高橋 遼*; 前川 禎通; 齊藤 英治

Physical Review B, 92(17), p.174424_1 - 174424_4, 2015/11

 被引用回数:14 パーセンタイル:36.69(Materials Science, Multidisciplinary)

We report the observation of the Barnett effect in paramagnetic states by mechanically rotating gadolinium (Gd) metal with a rotational frequency of up to 1.5 kHz above the Curie temperature. An in situ magnetic measurement setup comprising a high-speed rotational system and a fluxgate magnetic sensor was developed for the measurement. Temperature dependence of the observed magnetization follows that of paramagnetic susceptibility, indicating that any emergent magnetic field is proportional to the rotational frequency and is independent of temperature. From the proportionality constant of the emergent field, the gyromagnetic ratio of Gd is calculated to be -29 $$pm$$ 5 GHz/T. This study revisits the primordial issue of magnetism with modern technologies to shed new light on the fundamental spin-rotation coupling.

論文

Line splitting by mechanical rotation in nuclear magnetic resonance

針井 一哉; 中堂 博之; 小野 正雄; 松尾 衛; 家田 淳一; 岡安 悟; 前川 禎通; 齊藤 英治

Japanese Journal of Applied Physics, 54(5), p.050302_1 - 050302_3, 2015/05

 被引用回数:7 パーセンタイル:57.69(Physics, Applied)

Nuclear magnetic resonance (NMR) measurements for a nuclear spin 1/2 system in an external magnet field and mechanical rotation in kHz range are reported. NMR signals are measured by the synchronous rotation of a sample and a detector coil under the condition that the rotation axis is perpendicular to the external field. NMR line splits into two despite the system having a single Zeeman level separation. We analytically show that the splitting originates in the nuclear spin motion under mechanical rotation, and is determined by only the angular velocity of the rotation without any material parameters.

論文

Rotational Doppler effect and Barnett field in spinning NMR

中堂 博之; 針井 一哉; 松尾 衛; 家田 淳一; 小野 正雄; 前川 禎通; 齊藤 英治

Journal of the Physical Society of Japan, 84(4), p.043601_1 - 043601_4, 2015/04

 被引用回数:12 パーセンタイル:27.8(Physics, Multidisciplinary)

We report the observation of the rotational Doppler effect using nuclear magnetic resonance (NMR). We have developed a coil-spinning technique that enables measurements by rotating a detector and fixing a sample. We found that the rotational Doppler effect gives rise to NMR frequency shifts equal to the rotation frequency. We formulate the rotational Doppler effect and the Barnett field using a vector model for the nuclear magnetic moment. This formulation reveals that, with just the sample rotating, both effects cancel each other, thereby explaining the absence of an NMR frequency shift in conventional sample-spinning NMR measurements.

論文

Observation of Barnett fields in solids by nuclear magnetic resonance

中堂 博之; 小野 正雄; 針井 一哉; 松尾 衛; 家田 淳一; 春木 理恵*; 岡安 悟; 前川 禎通; 安岡 弘志; 齊藤 英治

Applied Physics Express, 7(6), p.063004_1 - 063004_4, 2014/06

 被引用回数:30 パーセンタイル:16.64(Physics, Applied)

電気的に中性な物体であっても、回転する物体中の粒子には磁場が生じることが予言されている。この磁場をバーネット磁場という。我々は核磁気共鳴法が固体中に生じたバーネット磁場を測定できることを示す。我々は試料とNMR検出コイルを同じ早さで回転させると核磁気モーメントの符号を反映したNMRシフトが生じることを見いだした。この結果はバーネット磁場の直接的証拠である。NMRを用いたバーネット磁場の測定は未知の核磁気モーメントの符号を決定できる。

論文

Unidirectional spin-wave heat conveyer

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

 被引用回数:84 パーセンタイル:4.17(Chemistry, Physical)

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

論文

Mechanical generation of spin current by spin-rotation coupling

松尾 衛; 家田 淳一; 針井 一哉; 齊藤 英治; 前川 禎通

Physical Review B, 87(18), p.180402_1 - 180402_4, 2013/05

 被引用回数:42 パーセンタイル:12.27(Materials Science, Multidisciplinary)

弾性変形によって誘起される回転とスピンとの相互作用を用いたスピン流生成が可能であることを理論的に示す。この方法は磁場やスピン軌道相互作用を必要としない。非磁性体中で表面音波によって生成されるスピン流を拡張されたスピン拡散方程式によって計算した結果、スピン緩和時間の長い物質でより大きいスピン流が得られることがわかった。

論文

Interface induced inverse spin Hall effect in bismuth/permalloy bilayer

Hou, D.*; Qiu, Z.*; 針井 一哉; 梶原 瑛祐*; 内田 健一*; 藤川 安仁*; 中山 裕康*; 吉野 達郎*; 安 東秀*; 安藤 和也*; et al.

Applied Physics Letters, 101(4), p.042403_1 - 042403_4, 2012/07

 被引用回数:51 パーセンタイル:9.16(Physics, Applied)

ビスマス/パーマロイ二層膜における逆スピンホール効果をスピンポンピングを用いて室温下で測定した。その結果、強磁性共鳴の吸収線幅からビスマスが良いスピン吸収材であることわかった。また、二層膜の逆スピンホール電圧と抵抗値の測定により、ビスマス膜厚の増大とともに逆スピンホール電流が減少することを見いだした。これは白金/パーマロイのような従来の二層膜における逆スピンホール効果の理解とは異なるものである。ビスマス/パーマロイ界面のスピン伝導の変調を考慮することで、この逆スピンホール電流の膜厚依存性を定量的に説明できるモデルを構築した。

論文

Geometry dependence on inverse spin Hall effect induced by spin pumping in Ni$$_{81}$$Fe$$_{19}$$/Pt films

中山 裕康*; 安藤 和也*; 針井 一哉; 吉野 達郎*; 高橋 遼*; 梶原 瑛祐*; 内田 健一*; 藤川 安仁*; 齊藤 英治

Physical Review B, 85(14), p.144408_1 - 144408_7, 2012/04

 被引用回数:147 パーセンタイル:2.01(Materials Science, Multidisciplinary)

強磁性共鳴(FMR)によるスピンポンピングで誘起される逆スピンHall効果(ISHE)の形状依存性を定量的に調べた。Ni$$_{81}$$Fe$$_{19}$$/Pt薄膜のサイズと膜厚を変え、FMRスペクトルとISHEによって誘起される起電力を測定した。薄膜形状を変えるとISHEによって誘起される電流はシステマティックに変化する。スピンポンピングによって誘起されるISHEの膜厚依存性はNi$$_{81}$$Fe$$_{19}$$とPtでは異なっている。

論文

All-oxide system for spin pumping

Qiu, Z.*; 梶原 瑛祐*; 安藤 和也*; 藤川 安仁*; 内田 健一*; 田代 隆治*; 針井 一哉*; 吉野 達郎*; 齊藤 英治

Applied Physics Letters, 100(2), p.022402_1 - 022402_3, 2012/01

 被引用回数:27 パーセンタイル:21.47(Physics, Applied)

単純な酸化物のみからなる系においてスピン波共鳴によるスピンポンプを逆スピンホール効果(ISHE)を用いて詳しく調べた。ランタンドープのイットリウム鉄ガーネット(La:YIG)/インジウムスズ酸化物(ITO)の2層膜においてスピンポンプが生じスピン流がITO層に注入され、それがISHEを通じて起電力として観測される。この起電力は面外磁場角度と励起マイクロ波パワーに依存して観測されたが、これはISHEの理論予測とよい一致を示す。酸化物のみからなる系でのスピンポンプの発見は酸化物スピントロニクスの可能性を広げるものである。

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