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

TLDR

The authors develop a linear‑response theory for diffusive magnon spin and heat transport in magnetic insulators with metallic contacts and compare its predictions with YIG/Pt experiments to extract a magnon spin conductivity of 5 × 10⁵ S/m. Magnons are modeled by position‑dependent temperature and chemical potential obeying diffusion equations, with length scales and transport coefficients derived from a linearized Boltzmann equation. The model predicts that at room temperature long‑range transport in YIG is dominated by the magnon chemical potential, yielding a spin Seebeck coefficient that matches experiments and a magnon spin conductivity of 5 × 10⁵ S/m, confirming the chemical potential’s essential role. The study cites Cornelissen et al., Nat.

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.