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

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.