Spin-caloritronic signatures of soft magnons in bilayer CrSBr

TL;DR

This paper investigates how the magnon spin angular momentum in bilayer CrSBr varies with magnetic field and wave vector, revealing a divergence that produces a notable spin Seebeck response as a signature of soft magnons.

Contribution

It introduces a calculation of magnon spin angular momentum in layered antiferromagnets considering anisotropy and dipolar interactions, highlighting a divergence near magnon softening.

Findings

Magnon spin angular momentum diverges at field-induced magnon softening.

A peak in the thermal spin Seebeck response indicates soft magnons.

Anisotropy and dipolar interactions significantly influence magnon spin properties.

Abstract

Spin transport in magnetic insulators is often treated by assuming that magnons carry a fixed spin angular momentum of $\hbar$, which does not hold in general, however. Here we calculate the magnon spin angular momentum of a layered antiferromagnet as a function of applied magnetic field and wave vector. We show that the triaxial anisotropy and intralayer dipolar interactions in bilayer CrSBr renormalize the magnon spin angular momentum, which diverges upon field-induced magnon softening. This divergence gives rise to a pronounced peak in the thermal spin Seebeck response and provides a clear spin-caloritronic signature of soft magnons.