Magnon-polaron transport in magnetic insulators

TLDR

Yttrium iron garnet films exhibit higher acoustic than magnetic quality, as shown by Kikkawa et al., explaining their transport behavior. We theoretically study the effects of strong magnetoelastic coupling on the transport properties of magnetic insulators. We develop a Boltzmann transport theory for mixed magnon‑phonon modes (magnon polarons) to determine transport coefficients and spin diffusion length. Magnon‑polaron formation produces anomalous magnetic‑field and temperature dependence of the spin Seebeck effect when disorder scattering differs between magnetic and elastic subsystems, and we predict similar anomalies in spin and heat conductivity and non‑local spin transport experiments.

Abstract

We theoretically study the effects of strong magnetoelastic coupling on the transport properties of magnetic insulators. We develop a Boltzmann transport theory for the mixed magnon-phonon modes (magnon polarons) and determine transport coefficients and spin diffusion length. Magnon-polaron formation causes anomalous features in the magnetic field and temperature dependence of the spin Seebeck effect when the disorder scattering in the magnetic and elastic subsystems is sufficiently different. Experimental data by Kikkawa et al. [PRL 117, 207203 (2016)] on yttrium iron garnet films can be explained by an acoustic quality that is much better than the magnetic quality of the material. We predict similar anomalous features in the spin and heat conductivity and non-local spin transport experiments.