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Theory of the Spin Seebeck Effect

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Authors:
Hiroto Adachi
Hiroto Adachi
Hiroto Adachi
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Ken-ichi Uchida
Ken-ichi Uchida
Ken-ichi Uchida
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Eiji Saitoh
Eiji Saitoh
Eiji Saitoh
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Sadamichi Maekawa at RIKEN
Sadamichi Maekawa
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The spin Seebeck effect refers to the generation of a spin voltage caused by a temperature gradient in a ferromagnet, which enables the thermal injection of spin currents from the ferromagnet into an attached nonmagnetic metal over a macroscopic scale of several millimeters. The inverse spin Hall effect converts the injected spin current into a transverse charge voltage, thereby producing electromotive force as in the conventional charge Seebeck device. Recent theoretical and experimental efforts have shown that the magnon and phonon degrees of freedom play crucial roles in the spin Seebeck effect. In this article, we present the theoretical basis for understanding the spin Seebeck effect and briefly discuss other thermal spin effects.
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IOP PUBLISHING REPORTS ON PROGRESS IN PHYSICS
Rep. Prog. Phys. 76 (2013) 036501 (20pp) doi:10.1088/0034-4885/76/3/036501
Theory of the spin Seebeck effect
Hiroto Adachi1,2, Ken-ichi Uchida3,4, Eiji Saitoh1,2,4,5and
Sadamichi Maekawa1,2
1Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Ibaraki, Japan
2CREST, Japan Science and Technology Agency, Sanbancho, Tokyo 102-0075, Japan
3PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama 332-012, Japan
4Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
5WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
E-mail: adachi.hiroto@jaea.go.jp
Received 12 September 2012, in final form 23 December 2012
Published 19 February 2013
Online at stacks.iop.org/RoPP/76/036501
Abstract
The spin Seebeck effect refers to the generation of a spin voltage caused by a temperature
gradient in a ferromagnet, which enables the thermal injection of spin currents from the
ferromagnet into an attached nonmagnetic metal over a macroscopic scale of several
millimeters. The inverse spin Hall effect converts the injected spin current into a transverse
charge voltage, thereby producing electromotive force as in the conventional charge Seebeck
device. Recent theoretical and experimental efforts have shown that the magnon and phonon
degrees of freedom play crucial roles in the spin Seebeck effect. In this paper, we present the
theoretical basis for understanding the spin Seebeck effect and briefly discuss other thermal
spin effects.
This article was invited by Laura H Greene.
Contents
1. Introduction 1
2. Spin current 2
3. Spin Hall effect 3
4. Spin Seebeck effect 4
4.1. Brief summary of the spin Seebeck effect 4
4.2. Experimental details of the spin Seebeck effect 5
5. Linear-response theory of the spin Seebeck effect 5
5.1. Local picture of thermal spin injection by
magnons 5
5.2. Linear-response approach to the
magnon-driven spin Seebeck effect 7
5.3. Length scale associated with the spin Seebeck
effect 10
6. Phonon-drag contribution to the spin Seebeck effect 11
6.1. Acoustic spin pumping 11
6.2. Phonon drag in the spin Seebeck effect 12
7. Varieties of the spin Seebeck effect 14
7.1. Longitudinal spin Seebeck effect 14
7.2. Thermoelectric coating based on the spin
Seebeck effect 16
7.3. Position sensing via the spin Seebeck effect 16
8. Other thermal spintronic effects 17
8.1. Spin injection due to the spin-dependent
Seebeck effect 17
8.2. Seebeck effect in magnetic tunnel junctions 17
8.3. Magnon-drag thermopile 17
8.4. Thermal spin-transfer torque 17
8.5. Effects of heat current on magnon dynamics 18
8.6. Anomalous Nernst effect and spin Nernst effect 18
8.7. Thermal Hall effect of phonons and magnons 18
9. Conclusions and future prospects 18
Acknowledgments 19
References 19
1. Introduction
Generation of electromotive force by a temperature gradient
has been known for many years as the Seebeck effect [1]. In
recent years, a spin analog of the Seebeck effect has drawn
considerable attention in the field of spintronics, because
replacing charge transport with spin transport in modern solid-
state devices is a major issue in the spintronics community.
More than two decades ago, Johnson and Silsbee [2] published
a seminal theoretical study, in which they generalized the
0034-4885/13/036501+20$88.00 1© 2013 IOP Publishing Ltd Printed in the UK & the USA
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