Magnon kinetic theory of the antiferromagnetic Hanle effect

TL;DR

This paper develops a kinetic theory for magnon spin transport in antiferromagnets, explaining the magnonic Hanle effect and its asymmetric magnetic field dependence through polarization dynamics.

Contribution

It introduces a novel energy-resolved kinetic framework that combines magnon transport with polarization coherence, explaining experimental observations of the magnonic Hanle effect.

Findings

Polarization of magnons changes periodically with magnetic field.

The theory explains the asymmetry in the Hanle signal.

Provides a unified description of magnon transport and polarization dynamics.

Abstract

Motivated by the recently discovered magnonic Hanle effect in an insulating antiferromagnet [Wimmer et al., Phys. Rev. Lett. 125, 247204 (2020)], we develop a spin transport theory based on low-energy waves of antiferromagnetic N\'eel order. These waves have two polarizations, which we describe in analogy to optics using the Stokes vector on the Poincar\'e sphere. We find that the polarization, which encodes the magnon spin angular momentum, changes periodically with a frequency that is nonlinear in the magnetic field. This explains the observed asymmetry in the Hanle signal as a function of the magnetic field, along with other salient experimental features. By providing an energy-resolved description of the spin injection, our theory combines the kinetic transport of magnons with the coherent dynamics of their polarization in an intuitive way. This opens a general perspective on a coherent control of magnonic spin density in collinear antiferromagnets.