# Nonlocal magnon-polaron transport in yttrium iron garnet

## TL;DR

This study investigates nonlocal magnon-polaron transport in yttrium iron garnet, revealing that magnon-polaron resonances can suppress the spin Seebeck effect, providing new insights into magnon-phonon interactions.

## Contribution

It reports the first observation of magnon-polarons in nonlocal spin injection/detection devices and explains their effect on the spin Seebeck effect using finite element modeling.

## Key findings

- Magnon-polaron resonances can suppress the nonlocal SSE.
- The suppression depends on injector-detector spacing and temperature.
- Finite element modeling explains the competition between SSE and spin diffusion.

## Abstract

The spin Seebeck effect (SSE) is observed in magnetic insulator|heavy metal bilayers as an inverse spin Hall effect voltage under a temperature gradient. The SSE can be detected nonlocally as well, viz. in terms of the voltage in a second metallic contact (detector) on the magnetic film, spatially separated from the first contact that is used to apply the temperature bias (injector). Magnon-polarons are hybridized lattice and spin waves in magnetic materials, generated by the magnetoelastic interaction. Kikkawa et al. [Phys. Rev. Lett. \textbf{117}, 207203 (2016)] interpreted a resonant enhancement of the local SSE in yttrium iron garnet (YIG) as a function of the magnetic field in terms of magnon-polaron formation. Here we report the observation of magnon-polarons in \emph{nonlocal} magnon spin injection/detection devices for various injector-detector spacings and sample temperatures. Unexpectedly, we find that the magnon-polaron resonances can suppress rather than enhance the nonlocal SSE. Using finite element modelling we explain our observations as a competition between the SSE and spin diffusion in YIG. These results give unprecedented insights into the magnon-phonon interaction in a key magnetic material.