Short-range thermal magnon diffusion in magnetic garnet
Kyongmo An, Ryuhei Kohno, Nicolas M. Thiéry, Derek Reitz, L. Vila, V. V. Naletov, Nathan Beaulieu, J. Ben Youssef, G. de Loubens, Yaroslav Tserkovnyak, O. Klein
Abstract
Using the spin Seebeck effect (SSE), we study the propagation distance of thermally induced 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 heat-sinking 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, in other words, 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 thermally generated magnon transport, where a single decay length may not capture the behavior on all length scales.