Evidence for the role of the magnon energy relaxation length in the Spin Seebeck Effect

TL;DR

This study investigates how magnon energy relaxation length influences the spin Seebeck effect in YIG films, revealing two key length scales that govern thermal spin transport through temperature-dependent measurements.

Contribution

It provides experimental evidence for the existence of a magnon energy relaxation length, a novel insight into thermal spin transport mechanisms in magnetic insulators.

Findings

SSR is non-monotonic with YIG thickness

Data support two distinct length scales in magnon transport

Diffusive model explains the observed behavior

Abstract

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.