Magnons and Phonons Optically Driven Out of Local Equilibrium in a Magnetic Insulator

TL;DR

This study demonstrates optically induced local non-equilibrium between magnons and phonons in YIG, using micro-Brillouin light scattering to analyze magnon diffusion and advance understanding of spin-heat coupling in magnetic insulators.

Contribution

It provides the first direct experimental evidence of optically driven non-equilibrium between magnons and phonons in a magnetic insulator and measures magnon diffusion length.

Findings

Established non-equilibrium between magnons and phonons in YIG.

Measured magnon diffusion length using BLS.

Enhanced understanding of spin-heat coupling phenomena.

Abstract

Magnons are the energy quanta of fundamental spin excitations, namely spin waves, and they can make a considerable contribution to energy transport in some magnetic materials in a similar manner as lattice vibration waves or phonons. The coupling and possible non-equilibrium between magnons and other energy carriers have been used to explain several recently discovered thermally driven spin transport and energy conversion phenomena. Here, we report experiments in which local non-equilibrium between magnons and phonons in a single crystalline bulk magnetic insulator, Y3Fe5O12 (yttrium iron garnet, or YIG), has been created optically within a focused laser spot and probed directly with the use of micro-Brillouin light scattering (BLS). By analyzing the experimental results with a thermally induced magnon diffusion model, we obtain the magnon diffusion length of thermal magnons. By explicitly establishing non-equilibrium between magnons and phonons, our studies represent an important step toward a quantitative understanding of various spin-heat coupling phenomena.