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論文

Temperature-variable apparatus for measuring Barnett field

埋田 真樹; 中堂 博之; 今井 正樹; 佐藤 奈々; 齊藤 英治

Review of Scientific Instruments, 94(6), p.063906_1 - 063906_8, 2023/06

https://doi.org/10.1063/5.0142318
 被引用回数：0 パーセンタイル：0(Instruments & Instrumentation)

We have developed experimental equipment for observing the Barnett effect, in which mechanical rotation magnetizes an object, at low temperatures. A sample in a rotor is rotated bidirectionally using a temperature-controlled high-pressure gas. The stray field generated from the sample due to the Barnett effect was detected using a fluxgate magnetic sensor with a sensitivity on the order of several picoteslas, even at low temperatures. By replacing the rotor with a solenoid coil, the magnetic susceptibility of the sample was estimated from the stray field to be of the same order of magnitude as that due to the Barnett effect. The Barnett field was estimated using the dipole model. To assess the performance of the setup at low temperatures, measurements were performed on commercial magnetite (Fe$$_3$$O$$_4$$) nanogranules. We confirmed the accordance of the $$it{g'}$$ factor between the experimental results using the present setup and those of our previous study performed at room temperature.

論文

Spin and spin current; From fundamentals to recent progress

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

https://doi.org/10.1063/5.0133335
 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.

論文

Observation of the angular momentum compensation by Barnett effect and NMR

中堂 博之; 今井 正樹; 松尾 衛; 前川 禎通; 齊藤 英治

Journal of the Physical Society of Japan, 90(8), p.081003_1 - 081003_11, 2021/08

https://doi.org/10.7566/JPSJ.90.081003
 被引用回数：3 パーセンタイル：41.09(Physics, Multidisciplinary)

We demonstrate observation of the angular momentum compensation temperature $$T_{rm A}$$, at which the net angular momentum is quenched in ferrimagnets. Using the Barnett effect, in which an object is magnetized by mechanical rotation owing to spin-rotation coupling, we measure $$T_{rm A}$$ in the Ho$$_{3-x}$$Dy$$_{x}$$Fe$$_{5}$$O$$_{12}$$ system. We determine $$T_{rm A}$$ to be 240 K in Ho$$_{3}$$Fe$$_{5}$$O$$_{12}$$ (HoIG). We find that $$T_{rm A}$$ increases with Dy content and show that $$T_{rm A}$$ of Ho$$_{1.5}$$Dy$$_{1.5}$$Fe$$_{5}$$O$$_{12}$$ corresponds with room temperature. We also demonstrate that $$^{57}$$Fe-NMR measurements can be applied to explore domain wall dynamics in HoIG. We find that the NMR intensity exhibits a maximum at $$T_{rm A}$$ in the multi-domain state. We provide a simple model for describing this NMR signal enhancement caused by enhancement of domain-wall mobility at $$T_{rm A}$$.

論文

Barnett field, rotational Doppler effect, and Berry phase studied by nuclear quadrupole resonance with rotation

中堂 博之; 松尾 衛*; 前川 禎通*; 齊藤 英治

Physical Review B, 103(17), p.174308_1 - 174308_10, 2021/05

https://doi.org/10.1103/PhysRevB.103.174308
 被引用回数：5 パーセンタイル：44.86(Materials Science, Multidisciplinary)

We report the observation of the Barnett field, rotational Doppler effect, and Berry phase using the rotating nuclear quadrupole resonance (NQR) methods. We have developed coil-spinning techniques that enable us to systematically study the effects of rotation in setups involving rotation of the signal detector, rotation of the sample, and simultaneous rotation of both the signal detector and sample. Applying these setups to NQR measurements, we observe NQR line splittings in which the spectral structures are clearly distinct among the setups. By analyzing these structures, we clarify the origin of the NQR line splittings and discuss the relationship between the rotational Doppler effect, Barnett field effect, and Berry phase in terms of the rotational degrees of freedom, such as the relative rotation and the sample rotation itself, and the observation frame of reference. We also provide clear evidence of the difference between the rotational Doppler effect and the Barnett field, and the equivalence of the Barnett field and the Berry phase.

論文

Reply to "Comment on 'Observation of Barnett fields in solids by nuclear magnetic resonance'" [Appl. Phys. Express 7, 063004 (2014)]

中堂 博之; 松尾 衛*; 針井 一哉*; 前川 禎通*; 齊藤 英治

Applied Physics Express, 13(10), p.109102_1 - 109102_2, 2020/10

https://doi.org/10.35848/1882-0786/abb343
 被引用回数：3 パーセンタイル：52.38(Physics, Applied)

バーネット効果とは物体を回転させるとその物体が磁化する現象である。これは磁気モーメントに対して回転座標系での慣性力として磁場が働くと解釈できる。その磁場をバーネット磁場と呼ぶ。バーネット磁場は慣性力であるために、高速で回転する物体と同じ速度で回転する測定系が必要である。我々は新規にコイル回転法を独自開発し、その共振回路を用いて核磁気共鳴法(NMR)測定を行ったところ、核磁気モーメントに働くバーネット磁場によってNMRの共鳴周波数が回転数に比例してシフトするという結果を得た。この成果は2014年にApplied Physics Expressに掲載されたが、2018年の夏、Jean Jeener人物から、我々が測定したものはバーネット磁場ではなく、コイルを回転させた事による人為的な効果であるとの批判が出た。本論文はこれに対する我々の返答である。

論文

角運動量物性としてのバーネット効果

中堂 博之; 今井 正樹

固体物理, 55(9), p.435 - 443, 2020/09

バーネット効果とは物体を回転させるとその物体が磁化するという1915年に発見された効果である。我々はここ10年間にわたって、スピントロニクスの文脈からこの効果を見直し、最先端のテクノロジーを用いてより高性能、高機能化した装置を用いて現代によみがえらせた。本レビューは装置開発当時から物体中の角運動量測定の成功に至るまでを、マル秘エピソードを交えてまとめたものである。

論文

Enhancement of domain-wall mobility detected by NMR at the angular momentum compensation temperature

今井 正樹; 中堂 博之; 松尾 衛; 前川 禎通; 齊藤 英治

Physical Review B, 102(1), p.014407_1 - 014407_5, 2020/07

https://doi.org/10.1103/PhysRevB.102.014407
 被引用回数：6 パーセンタイル：38.95(Materials Science, Multidisciplinary)

The angular momentum compensation temperature $$T_{rm A}$$ of ferrimagnets has attracted much attention because of high-speed magnetic dynamics near $$T_{rm A}$$. We show that NMR can be used to investigate domain wall dynamics near $$T_{rm A}$$ in ferrimagnets. We performed $$^{57}$$Fe-NMR measurements on the ferrimagnet Ho$$_3$$Fe$$_5$$O$$_{12}$$ with $$T_{rm A}$$ = 245 K. In a multi-domain state, the NMR signal is enhanced by domain wall motion. We found that the NMR signal enhancement shows a maximum at $$T_{rm A}$$ in the multi-domain state. The NMR signal enhancement occurs due to increasing domain-wall mobility toward $$T_{rm A}$$. We develop the NMR signal enhancement model involves domain-wall mobility. Our study shows that NMR in multi-domain state is a powerful tool to determine $$T_{rm A}$$, even from a powder sample and it expands the possibility of searching for angular momentum-compensated materials.

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

https://doi.org/10.1038/s41467-020-16753-0
 被引用回数：18 パーセンタイル：80.01(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

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, p.2616_1 - 2616_5, 2019/06

https://doi.org/10.1038/s41467-019-10625-y
 被引用回数：28 パーセンタイル：81.46(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

https://doi.org/10.1063/1.5095166
 被引用回数：20 パーセンタイル：73.01(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

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

https://doi.org/10.1063/1.5041464
 被引用回数：18 パーセンタイル：65.6(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

https://doi.org/10.1016/j.jmmm.2017.06.101
 被引用回数：8 パーセンタイル：66.67(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

https://doi.org/10.1063/1.4979553
 被引用回数：12 パーセンタイル：50.89(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

https://doi.org/10.1063/1.4976998
 被引用回数：19 パーセンタイル：65.79(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

https://doi.org/10.1038/nphys3526
 被引用回数：108 パーセンタイル：96.36(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

https://doi.org/10.1103/PhysRevB.92.174424
 被引用回数：29 パーセンタイル：74.62(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

https://doi.org/10.7567/JJAP.54.050302
 被引用回数：13 パーセンタイル：49.9(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

https://doi.org/10.7566/JPSJ.84.043601
 被引用回数：18 パーセンタイル：72.24(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

https://doi.org/10.7567/APEX.7.063004
 被引用回数：44 パーセンタイル：84.37(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

Microscopic properties of the heavy-fermion superconductor PuCoIn$$_5$$ explored by nuclear quadrupole resonance

Koutroulakis, G.*; 安岡 弘志; 中堂 博之; Tobash, P. H.*; Mitchell, J. N.*; Bauer, E. D.*; Thompson, J. D.*

New Journal of Physics (Internet), 16, p.053019_1 - 053019_12, 2014/05

https://doi.org/10.1088/1367-2630/16/5/053019
 被引用回数：6 パーセンタイル：44.89(Physics, Multidisciplinary)

重い電子系超伝導体PuCoIn$$_5$$において、0.29K $$leq Tleq$$75Kの温度領域で$$^{115}$$In核四重極共鳴(NQR)測定を行ったので報告する。結晶学的に異なるInサイトのNQRパラメーターを決定し、その温度依存性を調べた。超伝導転移温度以下においてNQR周波数が温度に比例してシフトすることを明らかにし、これは複合対形成模型からの予想と一致する。核スピン格子緩和率$$T_1^{-1}(T)$$は$$T_c simeq $$2.3Kで超伝導転移を示し、$$T_c$$近傍においてab面内の異方的揺らぎが大きな強結合系超伝導であることを示している。$$T_1^{-1}$$の解析はPuCoIn$$_5$$は強結合系d波超伝導体であることを示している。

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