Short-range Thermal Magnon Diffusion in Magnetic Garnet

TL;DR

This study investigates short-range thermal magnon diffusion in magnetic garnet using the spin Seebeck effect, revealing a much smaller diffusion length than previously thought and emphasizing the complexity of magnon transport modeling.

Contribution

It provides the first direct measurement of submicron magnon diffusion length in magnetic garnet and highlights limitations of diffusive models for thermal magnon transport.

Findings

Magnon diffusion length is in the submicron range.

Thermal magnon transport cannot be fully described by a single diffusion length.

Short-range behavior differs significantly from long-range estimates.

Abstract

Using the spin Seebeck effect (SSE), we study the propagation distance of thermal spin currents inside a magnetic insulator thin film in the short-range regime. We disambiguate spin currents driven by temperature and chemical potential gradients by comparing the SSE signal before and after adding a thermalization capping layer on the same device. We report that the measured spin decay behavior near the heat source is well accounted for by a diffusion model where the magnon diffusion length is in submicron range, \textit{i.e.} two orders of magnitude smaller than previous estimates inferred from the long-range behavior. Our results highlight the caveat in applying a diffusive theory to describe thermal magnon transport, where a single decay length may not capture the behavior on all length scales.