Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

TL;DR

This paper develops a linear-response theory for magnon-driven spin and heat transport in magnetic insulators, emphasizing the role of the magnon chemical potential in long-range transport phenomena.

Contribution

It introduces a comprehensive diffusion model incorporating the magnon chemical potential, providing new insights into spin transport in magnetic insulators like YIG.

Findings

Long-range transport dominated by magnon chemical potential.

Extracted magnon spin conductivity of 5×10^5 S/m.

Model aligns with experimental spin Seebeck measurements.

Abstract

We develop a linear-response transport theory of diffusive spin and heat transport by magnons in magnetic insulators with metallic contacts. The magnons are described by a position dependent temperature and chemical potential that are governed by diffusion equations with characteristic relaxation lengths. Proceeding from a linearized Boltzmann equation, we derive expressions for length scales and transport coefficients. For yttrium iron garnet (YIG) at room temperature we find that long-range transport is dominated by the magnon chemical potential. We compare the model's results with recent experiments on YIG with Pt contacts [L.J. Cornelissen, et al., Nat. Phys. 11, 1022 (2015)] and extract a magnon spin conductivity of $\sigma_{m}=5\times10^{5}$ S/m. Our results for the spin Seebeck coefficient in YIG agree with published experiments. We conclude that the magnon chemical potential is an essential ingredient for energy and spin transport in magnetic insulators.