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Eiji Saitoh - One of the best experts on this subject based on the ideXlab platform.
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lock in thermography measurements of the spin peltier Effect in a compensated ferrimagnet and its comparison to the spin Seebeck Effect
Journal of Physics D, 2018Co-Authors: Ryo Iguchi, Ken-ichi Uchida, Eiji Saitoh, Shunsuke Daimo, A Yagmu, Stepha Geprags, Anthony Erb, R GrossAbstract:The spin Peltier Effect (SPE) in a junction comprising a gadolinium-iron-garnet (GdIG) slab and a Pt film has been investigated around the magnetization compensation temperature of GdIG by means of the lock-in thermography method. When a charge current is applied to the Pt layer, a spin current is generated across the Pt/GdIG interface via the spin Hall Effect in Pt. This spin current induces a heat current and a measurable temperature change near the Pt/GdIG interface due to the SPE. The SPE signal in the Pt/GdIG junction shows a sign change around the magnetization compensation temperature, demonstrating the similar temperature dependence of the SPE and the spin Seebeck Effect for the Pt/GdIG hybrid system.
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the bimodal distribution spin Seebeck Effect enhancement in epitaxial ni0 65zn0 35al0 8fe1 2o4 thin film
Applied Physics Letters, 2018Co-Authors: Maki Umeda, Takashi Kikkawa, Yasushi Shiomi, Ka Shen, R Ramos, Yao Chen, Hua Wang, Eiji SaitohAbstract:The temperature dependence of the spin Seebeck Effect (SSE) in epitaxial Ni0.65Zn0.35Al0.8Fe1.2O4 (NZA ferrite) thin film has been investigated systematically. The SSE at high fields shows a bimodal distribution enhancement from 3 K to 300 K and is well fitted with a double-peak Lorentzian function. We speculate the symmetric SSE enhancement in Pt/NZA ferrite bilayer, which is different from the magnon polarons induced asymmetric spikes in the SSE of Pt/YIG [T. Kikkawa et al. Phys. Rev. Lett. 117, 207203 (2016)], may result from the magnon-phonon interactions occurring at the intersections of the quantized magnon and phonon dispersions. The SSE results are helpful for the investigation of the magnon-phonon interaction in the magnetic ultrathin films.The temperature dependence of the spin Seebeck Effect (SSE) in epitaxial Ni0.65Zn0.35Al0.8Fe1.2O4 (NZA ferrite) thin film has been investigated systematically. The SSE at high fields shows a bimodal distribution enhancement from 3 K to 300 K and is well fitted with a double-peak Lorentzian function. We speculate the symmetric SSE enhancement in Pt/NZA ferrite bilayer, which is different from the magnon polarons induced asymmetric spikes in the SSE of Pt/YIG [T. Kikkawa et al. Phys. Rev. Lett. 117, 207203 (2016)], may result from the magnon-phonon interactions occurring at the intersections of the quantized magnon and phonon dispersions. The SSE results are helpful for the investigation of the magnon-phonon interaction in the magnetic ultrathin films.
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spin Seebeck Effect in the polar antiferromagnet α cu 2 v 2 o 7
Physical Review B, 2017Co-Authors: Yuki Shiomi, Rina Takashima, Daisuke Okuyama, G Gitgeatpong, P Piyawongwatthana, K Matan, T J Sato, Eiji SaitohAbstract:Spin currents in antiferromagnetic materials have recently attracted much interest in the field of spintronics. Although the thermal generation Effect of spin currents, as in the spin Seebeck Effect (SSE), is powerful for their study, the SSE in antiferromagnets has been experimentally studied only for Cr${}_{2}$O${}_{3}$ and MnF${}_{2}$. In this work, the authors experimentally observe the SSE in the polar antiferromagnet \ensuremath{\alpha}-Cu${}_{2}$V${}_{2}$O${}_{7}$. Comparison of the experimental results with calculations using magnetic parameters determined by neutron scattering studies reveals that the magnon scattering plays an important role in the antiferromagnetic SSE observed in \ensuremath{\alpha}-Cu${}_{2}$V${}_{2}$O${}_{7}$.
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concomitant enhancement of the longitudinal spin Seebeck Effect and the thermal conductivity in a pt yig pt system at low temperatures
Physical Review B, 2017Co-Authors: Ryo Iguchi, Ken-ichi Uchida, Shunsuke Daimon, Eiji SaitohAbstract:We report a simultaneous measurement of a longitudinal spin Seebeck Effect (LSSE) and thermal conductivity in a Pt/${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (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 ${S}_{\mathrm{LSSE}}g10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{V}/\mathrm{K}$, 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.
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concomitant enhancement of the longitudinal spin Seebeck Effect and the thermal conductivity in a pt yig pt system at low temperatures
Physical Review B, 2017Co-Authors: Ryo Iguchi, Ken-ichi Uchida, Shunsuke Daimon, Eiji SaitohAbstract:We report a simultaneous measurement of a longitudinal spin Seebeck Effect (LSSE) and thermal conductivity in a Pt/${\rm Y_{3}Fe_{5}O_{12}}$ (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, differently from previous reports. The maximum LSSE coefficient is found to be $S{\rm_{LSSE}}>10\ \mu{\rm V/K}$, 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.
Joseph P. Heremans - One of the best experts on this subject based on the ideXlab platform.
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evidence for the role of the magnon energy relaxation length in the spin Seebeck Effect
Physical Review B, 2018Co-Authors: Arati Prakash, Jack Brangham, Fengyuan Yang, Benedetta Flebus, Yaroslav Tserkovnyak, Joseph P. HeremansAbstract:Temperature-dependent spin Seebeck Effect data on Pt|yttrium iron garnet (YIG) (${\mathrm{Y}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$)|gallium gadolinium garnet ($\mathrm{G}{\mathrm{d}}_{3}\mathrm{G}{\mathrm{a}}_{5}{\mathrm{O}}_{12}$) are reported for YIG films of various thicknesses. The Effect is reported as a spin Seebeck resistivity (SSR), the inverse spin-Hall field divided by the heat flux, to circumvent uncertainties about temperature gradients inside the films. The SSR is a nonmonotonic function of YIG thickness. A diffusive model for magnon transport demonstrates how these data give evidence for the existence of two distinct length scales in thermal spin transport, a spin-diffusion length, and a magnon energy relaxation length.
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evidence for the role of the magnon energy relaxation length in the spin Seebeck Effect
arXiv: Materials Science, 2017Co-Authors: Arati Prakash, Jack Brangham, Fengyuan Yang, Benedetta Flebus, Yaroslav Tserkovnyak, Joseph P. HeremansAbstract:Temperature-dependent spin-Seebeck Effect data on Pt|YIG (Y$_3$Fe$_5$O$_{12}$)|GGG (Gd$_3$Ga$_5$O$_{12}$) are reported for YIG films of various thicknesses. The Effect is reported as a spin-Seebeck resistivity (SSR), the inverse spin-Hall field divided by the heat flux, to circumvent uncertainties about temperature gradients inside the films. The SSR is a non-monotonic function of YIG thickness. A diffusive model for magnon transport demonstrates how these data give evidence for the existence of two distinct length scales in thermal spin transport, a spin diffusion length and a magnon energy relaxation length.
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Effect of the magnon dispersion on the longitudinal spin Seebeck Effect in yttrium iron garnets
Physical Review B, 2015Co-Authors: Hyungyu Jin, Stephen R Boona, Zihao Yang, R C Myers, Joseph P. HeremansAbstract:We study the temperature dependence of the longitudinal spin Seebeck Effect (LSSE) in an yttrium iron garnet ${\mathrm{Y}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$ (YIG)/Pt system for samples of different thicknesses. In this system, the thermal spin torque is magnon driven. The LSSE signal peaks at a specific temperature that depends on the YIG sample thickness. We also observe freeze-out of the LSSE signal at high magnetic fields, which we attribute to the opening of an energy gap in the magnon dispersion. We observe partial freeze-out of the LSSE signal even at room temperature, where ${k}_{B}T$ is much larger than the gap. This suggests that a subset of the magnon population with an energy below ${k}_{B}{T}_{C} ({T}_{C}\ensuremath{\sim}40\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ contributes disproportionately to the LSSE; at temperatures above ${T}_{C}$, we label these magnons subthermal magnons. The $T$ dependence of the LSSE at temperatures below the maximum is interpreted in terms of an empirical model that ascribes most of the temperature dependence to that of the thermally driven magnon flux, which is related to the details of the magnon dispersion.
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giant spin Seebeck Effect in a non magnetic material
Nature, 2012Co-Authors: Christopher M Jaworski, R C Myers, Ezekiel Johnstonhalperin, Joseph P. HeremansAbstract:A giant spin Seebeck Effect—three orders of magnitude greater than previously detected—has been observed in a non-magnetic material, InSb; the proposed mechanism relies only on phonon drag and spin–orbit interactions in a spin-polarized system, not on magnetic exchange. Heat cycles provide almost all of the energy that a modern civilization consumes. The thermoelectric cycle, a latecomer compared with steam and gases, generates electrical power through the Seebeck Effect, whereby an electric voltage is generated when a conductor is placed in a temperature gradient. The 2008 discovery of the spin Seebeck Effect ( go.nature.com/dlvhz2 ) — whereby a thermal gradient applied to a spin-polarized material leads to a spatially varying transverse spin current in an adjacent non-spin-polarized material — led to a new line of research in spintronics. In this issue of Nature, Jaworski et al. describe something similar but three orders of magnitude more powerful, a 'giant spin Seebeck Effect' in a material (indium antimonide, InSb) that is non-magnetic but that has strong spin–orbit coupling and phonon–electron drag. They propose a mechanism for this phenomenon that relies on spin polarization only, not on magnetic exchange. The results, say the authors, show that the spin Seebeck Effect can be of a magnitude that may make spin-based thermal-energy converters a reality, and possibly competitive with existing technologies. The spin Seebeck Effect is observed when a thermal gradient applied to a spin-polarized material leads to a spatially varying transverse spin current in an adjacent non-spin-polarized material, where it gets converted into a measurable voltage. It has been previously observed with a magnitude of microvolts per kelvin in magnetically ordered materials, ferromagnetic metals1, semiconductors2 and insulators3. Here we describe a signal in a non-magnetic semiconductor (InSb) that has the hallmarks of being produced by the spin Seebeck Effect, but is three orders of magnitude larger (millivolts per kelvin). We refer to the phenomenon that produces it as the giant spin Seebeck Effect. Quantizing magnetic fields spin-polarize conduction electrons in semiconductors by means of Zeeman splitting, which spin–orbit coupling amplifies by a factor of ∼25 in InSb. We propose that the giant spin Seebeck Effect is mediated by phonon–electron drag, which changes the electrons’ momentum and directly modifies the spin-splitting energy through spin–orbit interactions. Owing to the simultaneously strong phonon–electron drag and spin–orbit coupling in InSb, the magnitude of the giant spin Seebeck voltage is comparable to the largest known classical thermopower values.
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spin Seebeck Effect a phonon driven spin distribution
Physical Review Letters, 2011Co-Authors: Christopher M Jaworski, R C Myers, J Yang, Shawn Mack, D D Awschalom, Joseph P. HeremansAbstract:Here we report on measurements of the spin-Seebeck Effect in GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck Effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.
Ken-ichi Uchida - One of the best experts on this subject based on the ideXlab platform.
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lock in thermography measurements of the spin peltier Effect in a compensated ferrimagnet and its comparison to the spin Seebeck Effect
Journal of Physics D, 2018Co-Authors: Ryo Iguchi, Ken-ichi Uchida, Eiji Saitoh, Shunsuke Daimo, A Yagmu, Stepha Geprags, Anthony Erb, R GrossAbstract:The spin Peltier Effect (SPE) in a junction comprising a gadolinium-iron-garnet (GdIG) slab and a Pt film has been investigated around the magnetization compensation temperature of GdIG by means of the lock-in thermography method. When a charge current is applied to the Pt layer, a spin current is generated across the Pt/GdIG interface via the spin Hall Effect in Pt. This spin current induces a heat current and a measurable temperature change near the Pt/GdIG interface due to the SPE. The SPE signal in the Pt/GdIG junction shows a sign change around the magnetization compensation temperature, demonstrating the similar temperature dependence of the SPE and the spin Seebeck Effect for the Pt/GdIG hybrid system.
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concomitant enhancement of the longitudinal spin Seebeck Effect and the thermal conductivity in a pt yig pt system at low temperatures
Physical Review B, 2017Co-Authors: Ryo Iguchi, Ken-ichi Uchida, Shunsuke Daimon, Eiji SaitohAbstract:We report a simultaneous measurement of a longitudinal spin Seebeck Effect (LSSE) and thermal conductivity in a Pt/${\rm Y_{3}Fe_{5}O_{12}}$ (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, differently from previous reports. The maximum LSSE coefficient is found to be $S{\rm_{LSSE}}>10\ \mu{\rm V/K}$, 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.
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concomitant enhancement of the longitudinal spin Seebeck Effect and the thermal conductivity in a pt yig pt system at low temperatures
Physical Review B, 2017Co-Authors: Ryo Iguchi, Ken-ichi Uchida, Shunsuke Daimon, Eiji SaitohAbstract:We report a simultaneous measurement of a longitudinal spin Seebeck Effect (LSSE) and thermal conductivity in a Pt/${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (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 ${S}_{\mathrm{LSSE}}g10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{V}/\mathrm{K}$, 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.
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flexible heat flow sensing sheets based on the longitudinal spin Seebeck Effect using one dimensional spin current conducting films
Scientific Reports, 2016Co-Authors: Akihiro Kirihara, Ken-ichi Uchida, Eiji Saitoh, Koichi Kondo, Masahiko Ishida, Kazuki Ihara, Yuma Iwasaki, Hiroko Someya, Asuka Matsuba, Naoharu YamamotoAbstract:Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck Effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE Effect, the longitudinal spin Seebeck Effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management.
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flexible heat flow sensing sheets based on the longitudinal spin Seebeck Effect using one dimensional spin current conducting films
arXiv: Materials Science, 2016Co-Authors: Akihiro Kirihara, Ken-ichi Uchida, Eiji Saitoh, Koichi Kondo, Masahiko Ishida, Kazuki Ihara, Yuma Iwasaki, Hiroko Someya, Asuka Matsuba, Naoharu YamamotoAbstract:We demonstrated a flexible thermoelectric (TE) sheet based on the longitudinal spin Seebeck Effect (LSSE) that is especially suitable for heat-flow sensing applications. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as ferrite plating. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors.
S. Maekawa - One of the best experts on this subject based on the ideXlab platform.
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Spin Current Noise of the Spin Seebeck Effect and Spin Pumping.
Physical Review Letters, 2018Co-Authors: Mamoru Matsuo, Yuichi Ohnuma, Takeo Kato, S. MaekawaAbstract:: We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck Effect and spin pumping in a normal-metal-(NM-)ferromagnet(FM) bilayer system. Starting with a simple ferromagnet-insulator-(FI-)NM interface model with both spin-conserving and non-spin-conserving processes, we derive general expressions of the spin current and the spin-current noise at the interface within second-order perturbation of the FI-NM coupling strength, and estimate them for a yttrium-iron-garnet-platinum interface. We show that the spin-current noise can be used to determine the Effective spin carried by a magnon modified by the non-spin-conserving process at the interface. In addition, we show that it provides information on the Effective spin of a magnon, heating at the interface under spin pumping, and spin Hall angle of the NM.
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separation of longitudinal spin Seebeck Effect from anomalous nernst Effect determination of origin of transverse thermoelectric voltage in metal insulator junctions
Physical Review B, 2013Co-Authors: Takashi Kikkawa, Hiroto Adachi, K Uchida, Shunsuke Daimon, Zhiyong Qiu, Yuki Shiomi, Dazhi Hou, Xiaofeng Jin, S. MaekawaAbstract:The longitudinal spin Seebeck Effect (LSSE) and the anomalous Nernst Effect (ANE) are investigated in various metal/insulator junction systems and a clear separation of the LSSE from the ANE induced by static magnetic proximity is demonstrated. This separation is realized by comparing transverse thermoelectric voltage in in-plane magnetized (IM) and perpendicularly magnetized (PM) configurations, where the LSSE appears only in the IM configuration while the ANE appears both in the IM and PM configurations. We show that, in Pt/Y${}_{3}$Fe${}_{5}$O${}_{12}$ samples, the LSSE voltage in the IM configuration is three orders of magnitude greater than the proximity-ANE contamination estimated from the data in the PM configuration. This quantitative voltage comparison between the IM and PM configurations is corroborated by systematic voltage measurements in Ni${}_{81}$Fe${}_{19}$/Gd${}_{3}$Ga${}_{5}$O${}_{12}$, Pt/Gd${}_{3}$Ga${}_{5}$O${}_{12}$, Au/Y${}_{3}$Fe${}_{5}$O${}_{12}$, and Au/Gd${}_{3}$Ga${}_{5}$O${}_{12}$ samples and by our phenomenological model calculation. The LSSE measurements in high magnetic field regions further confirm that the observed voltage in the Pt/Y${}_{3}$Fe${}_{5}$O${}_{12}$ and Au/Y${}_{3}$Fe${}_{5}$O${}_{12}$ samples is of magnon origin. We apply this voltage comparison method also to a Ni${}_{81}$Fe${}_{19}$/Y${}_{3}$Fe${}_{5}$O${}_{12}$ sample and show that both the LSSE and ANE exist in this sample.
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Spin Seebeck Effect in antiferromagnets and compensated ferrimagnets
2013Co-Authors: Yuichi Ohnuma, Eiji Saitoh, Hiroto Adachi, S. MaekawaAbstract:We theoretically investigate the spin Seebeck Effect (SSE) in antiferromagnets and ferrimagnets, and show that the SSE vanishes in antiferromagnets but survives in ferrimagnets even at the magnetization compensation point despite the absence of its saturation magnetization. The nonvanishing SSE in ferrimagnets stems from two nondegenerate magnons. We demonstrate that the magnitude of the SSE in ferrimagnets is unchanged across the magnetization compensation point.
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Thermal spin pumping and magnon-phonon-mediated spin-Seebeck Effect
2012Co-Authors: Ken-ichi Uchida, Takeru Ota, Takahiro Nonaka, Yasuyuki Kajiwara, S. Maekawa, Gerrit E W Bauer, Hiroto Adachi, Jiang Xiao, Eiji SaitohAbstract:The spin-Seebeck Effect (SSE) in ferromagnetic metals and insulators has been investigated systematically by means of the inverse spin-Hall Effect (ISHE) in paramagnetic metals. The SSE generates a spin voltage as a result of a temperature gradient in a ferromagnet, which injects a spin current into an attached paramagnetic metal. In the paramagnet, this spin current is converted into an electric field due to the ISHE, enabling the electric detection of the SSE. The observation of the SSE is performed in longitudinal and transverse configurations consisting of a ferromagnet/paramagnet hybrid structure, where thermally generated spin currents flowing parallel and perpendicular to the temperature gradient are detected, respectively. Our results explain the SSE in terms of a two-step process: (1) the temperature gradient creates a non-equilibrium state in the ferromagnet governed by both magnon and phonon propagations and (2) the non-equilibrium between magnons in the ferromagnet and electrons in the paramagnet at the contact interface leads to ``thermal spin pumping'' and the ISHE signal. The non-equilibrium state of metallic magnets (e.g., Ni81Fe19) under a temperature gradient is governed mainly by the phonons in the sample and the substrate, while in insulating magnets (e.g., Y3Fe5O12), both magnon and phonon propagations appear to be important. The phonon-mediated non-equilibrium that drives the thermal spin pumping is confirmed also by temperature-dependent measurements, giving rise to a giant enhancement of the SSE signals at low temperatures.
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long range spin Seebeck Effect and acoustic spin pumping
Nature Materials, 2011Co-Authors: K Uchida, Takeru Ota, S. Maekawa, Hiroto Adachi, Masaya Toda, Burkard Hillebrands, Eiji SaitohAbstract:Imagine that a metallic wire is attached to a part of a large insulator, which itself exhibits no magnetization. It seems impossible for electrons in the wire to register where the wire is positioned on the insulator. Here we found that, using a Ni₈₁Fe₁₉/Pt bilayer wire on an insulating sapphire plate, electrons in the wire recognize their position on the sapphire. Under a temperature gradient in the sapphire, surprisingly, the voltage generated in the Pt layer is shown to reflect the wire position, although the wire is isolated both electrically and magnetically. This non-local voltage is due to the coupling of spins and phonons: the only possible carrier of information in this system. We demonstrate this coupling by directly injecting sound waves, which realizes the acoustic spin pumping. Our finding provides a persuasive answer to the long-range nature of the spin Seebeck Effect, and it opens the door to 'acoustic spintronics' in which sound waves are exploited for constructing spin-based devices.
K Uchida - One of the best experts on this subject based on the ideXlab platform.
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magnon polarons in the spin Seebeck Effect
Physical Review Letters, 2016Co-Authors: Takashi Kikkawa, Ka Shen, K Uchida, Benedetta Flebus, R A Duine, Zhiyong Qiu, G Bauer, Eiji SaitohAbstract:Sharp structures in the magnetic field-dependent spin Seebeck Effect (SSE) voltages of Pt/Y_{3}Fe_{5}O_{12} at low temperatures are attributed to the magnon-phonon interaction. Experimental results are well reproduced by a Boltzmann theory that includes magnetoelastic coupling. The SSE anomalies coincide with magnetic fields tuned to the threshold of magnon-polaron formation. The Effect gives insight into the relative quality of the lattice and magnetization dynamics.
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complete suppression of longitudinal spin Seebeck Effect by frozen magnetization dynamics in y3fe5o12
Journal of the Physical Society of Japan, 2016Co-Authors: Takashi Kikkawa, K Uchida, Shunsuke Daimon, Eiji SaitohAbstract:The spin Seebeck Effect (SSE) in a Pt-film/Y3Fe5O12 (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.
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critical suppression of spin Seebeck Effect by magnetic fields
Physical Review B, 2015Co-Authors: Takashi Kikkawa, K Uchida, Shunsuke Daimon, Zhiyong Qiu, Yuki Shiomi, Eiji SaitohAbstract:The longitudinal spin Seebeck Effect (LSSE) in $\mathrm{Pt}/{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}\phantom{\rule{0.28em}{0ex}}(\mathrm{YIG})$ 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.
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intrinsic surface magnetic anisotropy in y 3 fe 5 o 12 as the origin of low magnetic field behavior of the spin Seebeck Effect
Physical Review B, 2015Co-Authors: Jun Ichiro Ohe, Takashi Kikkawa, K Uchida, Shunsuke Daimon, Zhiyong Qiu, Dazhi Hou, Eiji SaitohAbstract:The magnetic-field dependence of the longitudinal spin Seebeck Effect (LSSE) in a $\mathrm{Pt}/{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (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.
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quantitative temperature dependence of longitudinal spin Seebeck Effect at high temperatures
Physical Review X, 2014Co-Authors: Takashi Kikkawa, K Uchida, Asuka Miura, Junichiro Shiomi, Eiji SaitohAbstract:The growing field of spintronics is partially propelled by the spin Seebeck Effect, in which a spin current results from a temperature gradient. Researchers report temperature-dependent measurements of the spin Seebeck Effect in a previously unexplored temperature regime.
