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.
@article{arxiv.2008.10942,
title = {Short-range Thermal Magnon Diffusion in Magnetic Garnet},
author = {Kyongmo An and Ryuhei Kohno and Nicolas Thiery and Derek Reitz and Laurent Vila and Vladimir V. Naletov and Nathan Beaulieu and Jamal Ben Youssef and Grégoire de Loubens and Yaroslav Tserkovnyak and Olivier Klein},
journal= {arXiv preprint arXiv:2008.10942},
year = {2021}
}