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論文

Pseudotunnel magnetoresistance in twisted van der Waals Fe$$_3$$GeTe$$_2$$ homojunctions

小幡 玲二*; 齊藤 英治; 吉川 貴史; 他13名*

Advanced Materials, p.2411459_1 - 2411459_11, 2025/00

 被引用回数:0

Twistronics, a novel engineering approach involving the alignment of van der Waals (vdW) integrated two-dimensional materials at specific angles, has recently attracted significant attention. Novel nontrivial phenomena have been demonstrated in twisted vdW junctions (the so-called magic angle), such as unconventional superconductivity, topological phases, and magnetism. However, there have been only few reports on integrated vdW layers with large twist angles $$theta_t$$, such as twisted interfacial Josephson junctions using high-temperature superconductors. Herein, vdW homojunctions of the thin-magnetic flakes, Fe$$_{3}$$GeTe$$_{2}$$ (FGT), with large $$theta_t$$ ranging from 0 to 90 deg, without inserting any tunnel barriers are assembled. Nevertheless, these vdW homojunctions exhibit tunnel-magnetoresistance (TMR) like behavior (pseudo-TMR (PTMR) effect) with the ratios highly sensitive to the $$theta_t$$ values, revealing that the vdW gap at the junction interface between the twisted FGT layers behaves like a tunnel barrier and the $$theta_t$$ serves a control parameter for PTMR by drastically varying magnitudes of the lattice-mismatch and the subsequent appearance of antiferromagnetic (AFM) spin alignment. First-principles calculations considering vacuum gaps indicate strong dependence of TMR on the $$theta_t$$ driven by the sixfold screw rotational symmetry of bulk FGT. The present homojunctions hold promise as a platform for novel AFM spin-dependent phenomena and spintronic applications.

論文

Atom-vacancy-defect-derived electric hysteresis loops and stochastic low-frequency noises in few-atom layer MoS$$_2$$

小杉 美央子*; 吉川 貴史; 齊藤 英治; 他10名*

ACS Applied Materials & Interfaces, 16(46), p.64190 - 64196, 2024/11

 被引用回数:0 パーセンタイル:0.00(Nanoscience & Nanotechnology)

Atom-vacancy-defects present in various materials yield numerous interesting physical phenomena, even obstructing high performance in some cases. On the other hand, their valuable applications to novel devices, such as nitrogen vacancy centers in diamond for quantum bits, have gathered significant attention. In particular, these tendencies become more substantial in two-dimensional (2D) (atomically) thin van der Waals layers. However, correlations with various kinds of atom defects are still under exploration. Herein, we find the stochastic behaviors of large hysteresis loops with strong photoresponse in the static electrical properties in few-atom layer semiconductors, molybdenum disulfide (MoS$$_{2}$$). The temperature dependence and transmission electron microscopy reveal that they arise from pairs of two neighboring in-plane S-vacancy defects, which predominantly present only around the interface at the MoS$$_{2}$$ flake/substrate, with activation energies similar to 0.35 eV. The low-frequency ($$f$$) (LF) noise measurements clarify a high f shift in the two 1/$$f$$ 2-dependent regimes, implying stochastic behaviors of electric charges through the S-vacancy pairs with high-speed charge(spin) transitions across low kinetic energy barriers between narrow discrete states. The shallow energy sates are formed from the highly uniform S-vacancy pairs interacting with Mo atoms, which act like quantum dots. The observed stochastic operation holds promise for various application, particularly for probabilistic neuromorphic computation in artificial intelligence.

論文

Enhanced magnetism derived from pore-edge spins in thin Fe$$_3$$GeTe$$_2$$ nanomeshes

小幡 玲二*; 吉川 貴史*; 齊藤 英治; 他7名*

Nanotechnology, 35(47), p.475601_1 - 475601_9, 2024/11

 被引用回数:1 パーセンタイル:0.00(Nanoscience & Nanotechnology)

The growth of two-dimensional van der Waals magnetic materials presents attractive opportunities for exploring new physical phenomena and valuable applications. Among these materials, Fe$$_{3}$$GeTe$$_{2}$$ (FGT) exhibits a variety of remarkable properties and has garnered significant attention. Herein, we have for the first time created a nanomesh structure-a honeycomb-like array of hexagonal nanopores-with the zigzag pore-edge atomic structure on thin FGT flakes with and without oxidation of the pore edges. It is revealed that the magnitude of ferromagnetism (FM) significantly increases in both samples compared with bulk flakes without nanomeshes. Critical temperature annealing results in the formation of zigzag pore edges and interpore zigzag-edge nanoribbons. We unveil that the non-oxide (O) termination of the Fe dangling bonds on these zigzag edges enhances FM behavior, while O-termination suppresses this FM by introducing antiferromagnetic behavior through edge O-Fe coupling. FGT nanomeshes hold promise for the creation of strong FM and their effective application in magnetic and spintronic systems.

論文

Tunable sigmoid behavior of a magnon-based parametron using a Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt bilayer disk

Emdi, G.*; 日置 友智*; 巻内 崇彦*; 齊藤 英治

Physical Review Applied (Internet), 22(3), p.L031002_1 - L031002_6, 2024/09

 被引用回数:0 パーセンタイル:0.00(Physics, Applied)

Sigmoidal curve behavior of 0 and n state probability in a magnon parametron, using yttrium iron garnet (Y$$_3$$Fe$$_5$$O$$_{12}$$) thin disk, is systematically investigated. We demonstrate that the probability distribution can be tuned by bias and pump microwave power. Our numerical calculation that considers increasing damping due to four-magnon scattering processes reproduces the results well.

論文

Coexistence of quantum-spin-hall and quantum-hall-topological-insulating states in graphene/hBN on SrTiO$$_3$$ substrate

小幡 玲二*; 齊藤 英治; 吉川 貴史; 他7名*

Advanced Materials, 36(19), p.2311339_1 - 2311339_8, 2024/05

 被引用回数:0 パーセンタイル:0.00(Chemistry, Multidisciplinary)

SrTiO$$_{3}$$ (STO) substrate, a perovskite oxide material known for its high dielectric constant (epsilon), facilitates the observation of various (high-temperature) quantum phenomena. A quantum Hall topological insulating (QHTI) state, comprising two copies of QH states with antiparallel two ferromagnetic edge-spin overlap protected by the U(1) axial rotation symmetry of spin polarization, has recently been achieved in low magnetic field (B) even as high as approximate to 100 K in a monolayer graphene/thin hexagonal boron nitride (hBN) spacer placed on an STO substrate, thanks to the high epsilon of STO. Despite the use of the heavy STO substrate, however, proximity-induced quantum spin Hall (QSH) states in 2D TI phases, featuring a topologically protected helical edge spin phase within time-reversal-symmetry, is not confirmed. Here, with the use of a monolayer hBN spacer, it is revealed the coexistence of QSH (at B = 0T) and QHTI (at B not equal 0) states in the same single graphene sample placed on an STO, with a crossover regime between the two at low B. It is also classified that the different symmetries of the two nontrivial helical edge spin phases in the two states lead to different interaction with electron-puddle quantum dots, caused by a local surface pocket of the STO, in the crossover regime, resulting in a spin dephasing only for the QHTI state. The results obtained using STO substrates open the doors to investigations of novel QH spin states with different symmetries and their correlations with quantum phenomena. This exploration holds value for potential applications in spintronic devices.

論文

Persistent magnetic coherence in magnets

巻内 崇彦*; 日置 友智*; 清水 祐樹*; 星 幸治郎*; Elyasi, M.*; 山本 慧; 横井 直人*; Serga, A. A.*; Hillebrands, B.*; Bauer, G. E. W.*; et al.

Nature Materials, 23(5), p.627 - 632, 2024/05

 被引用回数:8 パーセンタイル:96.91(Chemistry, Physical)

When excited, a magnetization in a magnet precesses around the field in an anticlockwise manner on a time scale governed by viscous magnetization damping, after which any information carried by the initial actuation seems to be lost. The damping appears to be a fundamental bottleneck for the use of magnets in information processing. Nevertheless, here we demonstrate recall of the magnetization-precession phase after times that far exceed the damping time scale by two orders of magnitude using dedicated two-colour microwave pump-and-probe experiments for a Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ microstructured film. Time- resolved magnetization state tomography confirms the magnetic persistent coherence (MPC) by revealing a double-exponential decay of the magnetization correlation. We attribute MPC to a feedback effect, viz. coherent coupling of the uniform precession with long-lived excitations at the minima of the spin-wave dispersion relation. Our finding liberates magnetic systems from the strong damping in nanostructures tyranny that limits their use in coherent information storage and processing.

論文

Nonlinear enhancement of coherent magnetization dynamics

Elyasi, M.*; 山本 慧; 日置 友智*; 巻内 崇彦*; 清水 祐樹*; 齊藤 英治*; Bauer, G. E. W.*

Physical Review B, 109(18), p.L180402_1 - L180402_7, 2024/05

 被引用回数:0 パーセンタイル:0.00(Materials Science, Multidisciplinary)

Magnets are interesting materials for classical and quantum information technologies. However, the short decoherence and dephasing times that determine the scale and speed of information networks severely limit the appeal of employing the ferromagnetic resonance. Here we show that the lifetime and coherence of the uniform Kittel mode can be enhanced by three-magnon interaction-induced mixing with the long-lived magnons at the minima of the dispersion relation. Analytical and numerical calculations based on this model explain recent experimental results and predict experimental signatures of quantum coherence.

論文

Radio frequency discharge apparatus for studying spin transfer from solid surfaces to metastable helium gas

丸山 遥香*; 齊藤 英治; 他2名*

AIP Advances (Internet), 14(3), p.035217_1 - 035217_8, 2024/03

 被引用回数:0 パーセンタイル:0.00(Nanoscience & Nanotechnology)

We developed a radio frequency discharge apparatus for He gas to investigate the spin states of metastable helium (He$$^{*}$$) interacting with solid-state surfaces. Our apparatus consisted of a stainless steel vacuum chamber, in which a coil produced He$$^{*}$$ by discharging introduced He gas. The spin states of the He$$^{*}$$ were detected using optical pumping and probing techniques. The chamber was designed to accommodate various solid-state samples. We measured the He$$^{*}$$ polarization produced at a dielectric prism surface by total internal reflection of the circularly polarized pumping light. Our apparatus can be used to investigate possible spin transfer from various solid surfaces to He$$^{*}$$ atoms.

論文

Understanding spin currents from magnon dispersion and polarization; Spin-Seebeck effect and neutron scattering study on Tb$$_3$$Fe$$_5$$O$$_{12}$$

川本 陽*; 吉川 貴史; 齊藤 英治; 他9名*

Applied Physics Letters, 124(13), p.132406_1 - 132406_7, 2024/03

 被引用回数:3 パーセンタイル:88.42(Physics, Applied)

Magnon spin currents in the ferrimagnetic garnet Tb$$_{3}$$Fe$$_{5}$$O$$_{12}$$ with 4$$f$$ electrons were examined through the spin-Seebeck effect and neutron scattering measurements. The compound shows a magnetic compensation, where the spin-Seebeck signal reverses above and below $$T$$$$_{rm comp}$$ = 249.5(4) K. Unpolarized neutron scattering unveils two major magnon branches with finite energy gaps, which are well explained in the framework of spin-wave theory. Their temperature dependencies and the direction of the precession motion of magnetic moments, i.e., magnon polarization, defined using polarized neutrons, explain the reversal at $$T$$$$_{rm comp}$$ and decay of the spin-Seebeck signals at low temperatures. We illustrate an example that momentum- and energy-resolved microscopic information is a prerequisite to understand the magnon spin current.

論文

Electrical detection of parallel parametric amplification and attenuation in a Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt bilayer disk

Emdi, G.*; 日置 友智*; 星 幸治郎*; 齊藤 英治

Physical Review B, 108(14), p.L140410_1 - L140410_6, 2023/10

 被引用回数:2 パーセンタイル:36.13(Materials Science, Multidisciplinary)

We report a systematic quantitative evaluation of parametric amplification gain of magnetization dynamics in an yttrium iron garnet (Y$$_3$$Fe$$_5$$O$$_{12}$$) thin disk via ac spin pumping and the inverse spin Hall effect. We demonstrate its signature phase dependence where amplification and attenuation occur every i phase shift of the input signal. The results also show the pump-power dependence of the gain that is explained well by our theoretical model. Finally, the optimal conditions for amplification are investigated by measuring the magnetic field dependence, where we find the highest gain of 11.4 dB.

論文

Gate-tunable resistance drops related to local superconducting gaps in thin TaS$$_2$$ layers on SrTiO$$_3$$ substrates

小杉 美央子*; 齊藤 英治; 吉川 貴史*; 他11名*

APL Materials (Internet), 11(8), p.081106_1 - 081106_6, 2023/08

 被引用回数:1 パーセンタイル:18.74(Nanoscience & Nanotechnology)

Strontium titanate [SrTiO$$_{3}$$ (STO)], a perovskite oxide with an extremely high gate-tunable dielectric constant ($$varepsilon$$) due to quantum paraelectric phases, is attracting considerable attention for yielding various physical phenomena when two-dimensional (2D) layers are integrated. Superconductivity is such a typical phenomenon. However, the influence of the STO substrates on enhancing transition temperatures ($$T$$$$_{rm c}$$) for (atomically) thin 2D flakes attached to them has been rarely investigated. Here, we report gate-tunable and gradual four-terminal resistance drops with critical onset $$T$$ ($$T$$$$_{rm CR}$$) and scanning tunneling spectroscopy (STS) spectra in devices comprising thin TaS$$_{2}$$ flakes attached on monolayer hexagonal boron nitride (hBN) spacer/STO substrates. Observation of STS spectra confirms the presence of local superconducting gaps. (similar to 1.5 meV) with transition $$T$$($$T_{Delta rm C})$$ three-times higher than previous reports of $$T$$$$_{rm c}$$ under absent pressure and strong position dependence of $${Delta}$$. Depending on $$Delta$$ on back gate voltages ($$V$$$$_{rm bg}$$) and magnetic fields, there is a strong correlation between $$T$$$$_{rm CR}$$ and the onset $$T$$$$_{rm c}$$ of superconductivity, implying an enhancement of approximately five times compared with the previous highest-onset $$T$$$$_{rm c}$$ values without pressure as the applied $$V$$$$_{rm bg}$$ increases. The high onset $$T$$$$_{rm c}$$ and. are discussed based on screening of the long-range Coulomb interaction (CI) due to the high-$$varepsilon$$ of SrTiO$$_{3}$$, while the short-ranged CI remains strong in the 2D limit, causing the superconductivity. Using a monolayer hBN/SrTiO$$_{3}$$ substrate with $$V$$$$_{rm bg}$$ opens doors to $$T$$$$_{rm c}$$ enhancement in thin superconducting layers integrated on it and wide application due to the solid-state high-$$varepsilon$$ substrates.

論文

Switching of magnon parametric oscillation by magnetic field direction

堀部 聡平*; 清水 祐樹*; 星 幸治郎*; 巻内 崇彦*; 日置 友智*; 齊藤 英治

Applied Physics Express, 16(7), p.073001_1 - 073001_4, 2023/07

 被引用回数:1 パーセンタイル:18.74(Physics, Applied)

Parametric oscillation occurs when the resonance frequency of an oscillator is periodically modulated. Owing to time-reversal symmetry breaking in magnets, nonreciprocal magnons can be parametrically excited when spatial-inversion symmetry breaking is provided. This means that magnons with opposite propagation directions have different amplitudes. Here we demonstrate switching on and off the magnon parametric oscillation by reversing the external field direction applied to a Y$$_3$$Fe$$_5$$O$$_{12}$$ micro-structured film. The result originates from the nonreciprocity of surface mode magnons, leading to field-direction dependence of the magnon accumulation under nonuniform microwave pumping. Our numericalcalculation well reproduces the experimental result.

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

 被引用回数:1 パーセンタイル:20.80(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

Laser-induced creation of antiferromagnetic 180-degree domains in NiO/Pt bilayers

Meer, H.*; Wust, S.*; Schmitt, C.*; Herrgen, P.*; Fuhrmann, F.*; Hirtle, S.*; Bednarz, B.*; Rajan, A.*; Ramos, R.*; Ni$~n$o, M. A.*; et al.

Advanced Functional Materials, 33(21), p.2213536_1 - 2213536_6, 2023/05

 被引用回数:3 パーセンタイル:50.09(Chemistry, Multidisciplinary)

The antiferromagnetic order in heterostructures of NiO/Pt thin films can be modified by optical pulses. After the irradiation with laser light, the optically induced creation of antiferromagnetic domains can be observed by imaging the created domain structure utilizing the X-ray magnetic linear dichroism effect. The effect of different laser polarizations on the domain formation can be studied and used to identify a polarization-independent creation of 180$$^{circ}$$ domain walls and domains with 180$$^{circ}$$ different N$'e$el vector orientation. By varying the irradiation parameters, the switching mechanism can be determined to be thermally induced. This study demonstrates experimentally the possibility to optically create antiferromagnetic domains, an important step towards future functionalization of all optical switching mechanisms in antiferromagnets.

論文

Current-induced crystallisation in a Heusler-alloy-based giant magnetoresistive junction for neuromorphic potentiation

Zhou, Z.*; Frost, W.*; Lloyd, D. C.*; 関 剛斎*; 窪田 崇秀*; Ramos, R.*; 齊藤 英治; 高梨 弘毅; 廣畑 貴文*

Journal of Magnetism and Magnetic Materials, 571, p.170575_1 - 170575_5, 2023/04

 被引用回数:1 パーセンタイル:15.59(Materials Science, Multidisciplinary)

Recent development in neuromorphic computation allows us to achieve low power and highly efficient calculations better than the conventional von Neumann computation. In order to achieve realistic synaptic operation, potentiation to add weighting to strengthen a selected artificial synapse. Such functionality can be achieved by reducing the electrical resistance of the artificial synapse. Recently, a ferromagnetic Heusler alloy used in a magnetoresistive junction has been demonstrated to crystallise via the layer-by-layer mode by introducing an electrical current pulse. In this study, we have extended the current-induced crystallisation to a junction with epitaxially-grown Heusler alloy after post-annealing for crystallisation. By combining this potentiation functionality with the neuromorphic operation, realistic synaptic computation can be developed.

論文

Ginzburg-Landau action and polarization current in an excitonic insulator model of electronic ferroelectricity

安立 裕人*; 池田 直*; 齊藤 英治

Physical Review B, 107(15), p.155142_1 - 155142_10, 2023/04

 被引用回数:5 パーセンタイル:68.49(Materials Science, Multidisciplinary)

In comparison to transport of spin polarization in ferromagnets, transport of electric polarization in ferroelectrics remains less explored. Taking an excitonic insulator model of electronic ferroelectricity as a prototypical example, we theoretically investigate the low-energy dynamics and transport of electric polarization by microscopically constructing the Ginzburg-Landau action. We show that, because of the scalar nature of the excitonic order parameter, only the longitudinal fluctuations are relevant to the transport of electric polarization. We also formulate the electric-polarization diffusion equation, in which the electric-polarization current is defined purely electronically without recourse to the lattice degrees of freedom.

論文

Spin Seebeck effect; Sensitive probe for elementary excitation, spin correlation, transport, magnetic order, and domains in solids

吉川 貴史*; 齊藤 英治

Annual Review of Condensed Matter Physics, 14, p.129 - 151, 2023/03

 被引用回数:25 パーセンタイル:72.97(Physics, Condensed Matter)

The spin Seebeck effect (SSE) refers to the generation of a spin current as a result of a temperature gradient in a magnetic material, which can be detected electrically via the inverse spin Hall effect in a metallic contact. Since the discovery of the SSE in 2008, intensive studies on the SSE have been conducted to elucidate its origin. SSEs appear in a wide range of magnetic materials including ferro-, ferri-, and antiferromagnets and also paramagnets with classical or quantum spin fluctuation. SSE voltage reflects fundamental properties of a magnet, such as elementary excitation, static magnetic order, spin correlation, and spin transport. In this article, we review recent progress on the SSE in various systems, with particular emphasis on its emerging role as a probe of these magnetic properties in solids. We also briefly discuss the recently discovered nuclear SSE.

論文

Lanthanide and actinide ion complexes containing organic ligands investigated by surface-enhanced infrared absorption spectroscopy

平田 早紀子*; 日下 良二; 明地 省吾*; 為国 誠太*; 奥寺 洸介*; 浜田 昇賢*; 坂本 知優*; 本田 匠*; 松下 高輔*; 村松 悟*; et al.

Inorganic Chemistry, 62(1), p.474 - 486, 2023/01

 被引用回数:3 パーセンタイル:33.37(Chemistry, Inorganic & Nuclear)

A new technique, surface-enhanced infrared absorption (SEIRA) spectroscopy, was used for the structural investigation of lanthanide (Ln) and actinide (An) complexes containing organic ligands. We synthesized thiol derivatives of organic ligands with coordination sites similar to those of diglycolamide (DGA), Cyanex-272, and $$N,N,N',N'$$-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN), which have been used for separating Ln and An through solvent extraction. These ligands were attached on a gold surface deposited on an Si prism through S-Au covalent bonds; the gold surface enhanced the IR absorption intensity of the ligands. Aqueous solutions of Ln (Eu$$^{3+}$$, Gd$$^{3+}$$, Tb$$^{3+}$$) and An (Am$$^{3+}$$) ions were loaded onto the gold surface to form ion complexes. The IR spectra of the ion complexes were obtained using FT-IR spectroscopy in the attenuated total reflection mode. In this study, we developed a new sample preparation method for SEIRA spectroscopy that enabled us to obtain the IR spectra of the complexes with a small amount of ion solution (5 $$mu$$L). This is a significant advantage for the IR measurement of radiotoxic Am$$^{3+}$$ complexes. In the IR spectra of DGA, the band attributed to C=O stretching vibrations at $$sim$$1630 cm$$^{-1}$$ shifted to a lower wavenumber by $$sim$$20 cm$$^{-1}$$ upon complexation with Ln and An ions. Moreover, the amount of the red-shift was inversely proportional to the extraction equilibrium constant reported in previous studies on solvent extraction. The coordination ability of DGA toward Ln and An ions could be assessed using the band position of the C=O band. The Cyanex-272- and TPEN-like ligands synthesized in this report also showed noticeable SEIRA signals for Ln and An complexes. This study indicates that SEIRA spectroscopy can be used for the structural investigation of ion complexes and provides a microscopic understanding of selective extraction of Ln and An.

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

 被引用回数:20 パーセンタイル:94.98(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

Mechanism of paramagnetic spin Seebeck effect

大柳 洸一*; 高橋 三郎*; 吉川 貴史*; 齊藤 英治

Physical Review B, 107(1), p.014423_1 - 014423_8, 2023/01

 被引用回数:10 パーセンタイル:86.58(Materials Science, Multidisciplinary)

We have theoretically investigated the spin Seebeck effect (SSE) in a normal metal (NM)/paramagnetic insulator (PI) bilayer system. Through a linear response approach, we calculated the thermal spin pumping from PI to NM and backflow spin current from NM to PI, where the spin-flip scattering via the interfacial exchange coupling between conduction-electron spin in NM and localized spin in PI is taken into account. We found a finite spin current appears at the interface under the difference in the effective temperatures between spins in NM and PI, and its intensity increases by increasing the density of the localized spin S. Our model well reproduces the magnetic-field-induced reduction of the paramagnetic SSE in Pt/Gd$$_3$$Ga$$_5$$O$$_{12}$$ experimentally observed when the Zeeman energy is comparable to the thermal energy, which can be interpreted as the suppression of the interfacial spin-flip scattering. The present finding provides an insight into the mechanism of paramagnetic SSEs and the thermally induced spin-current generation in magnetic materials.

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