Influence of yttrium iron garnet thickness and heater opacity on the nonlocal transport of electrically and thermally excited magnons

TL;DR

This study investigates how YIG thickness and heater opacity affect nonlocal magnon transport, revealing a sign reversal in thermally generated magnons and estimating the bulk spin Seebeck coefficient through modeling.

Contribution

It provides new insights into the influence of YIG thickness and interface opacity on nonlocal magnon transport and introduces a finite element model to estimate the spin Seebeck coefficient.

Findings

Nonlocal signals decrease with increasing YIG thickness for electrically excited magnons.

Sign reversal occurs in thermally generated magnon signals depending on heater-detector distance.

Estimated bulk spin Seebeck coefficient at room temperature using 2D-FEM.

Abstract

We studied the nonlocal transport behavior of both electrically and thermally excited magnons in yttrium iron garnet (YIG) as a function of its thickness. For electrically injected magnons, the nonlocal signals decrease monotonically as the YIG thickness increases. For the nonlocal behavior of the thermally generated magnons, or the nonlocal spin Seebeck effect (SSE), we observed a sign reversal which occurs at a certain heater-detector distance, and it is influenced by both the opacity of the YIG/heater interface and the YIG thickness. Our nonlocal SSE results can be qualitatively explained by the bulk-driven SSE mechanism together with the magnon diffusion model. Using a two-dimensional finite element model (2D-FEM), we estimated the bulk spin Seebeck coefficient of YIG at room temperature. The quantitative disagreement between the experimental and modeled results indicates more complex processes going on in addition to magnon diffusion and relaxation, especially close to the contacts.