Thermal spin current and spin accumulation at ferromagnetic insulator/nonmagnetic metal interface

TL;DR

This paper theoretically investigates how thermal gradients at a FI/NM interface induce spin currents and accumulations, highlighting the role of interfacial electron-magnon interactions and the negligible effect of temperature gradients in the nonmagnetic metal.

Contribution

It introduces a theoretical model explaining spin current generation via interfacial electron-magnon scattering under thermal gradients, aligning well with experimental observations.

Findings

Spin currents are generated by temperature gradients in FI and across the interface.

Spin current induced by temperature gradients in NM is negligible.

Theoretical results agree with existing experimental data.

Abstract

Spin current injection and spin accumulation near a ferromagnetic insulator (FI)/nonmagnetic metal (NM) bilayer film under a thermal gradient is investigated theoretically. Using the Fermi golden rule and the Boltzmann equations, we find that FI and NM can exchange spins via interfacial electron-magnon scattering because of the imbalance between magnon emission and absorption caused by either non-equilibrium distribution of magnons or non-equilibrium between magnons and electrons. A temperature gradient in FI and/or a temperature difference across the FI/NM interface generates a spin current which carries angular momenta parallel to the magnetization of FI from the hotter side to the colder one. Interestingly, the spin current induced by a temperature gradient in NM is negligibly small due to the nonmagnetic nature of the non-equilibrium electron distributions. The results agree well with all existing experiments.