The Intrinsic Magnetization of Antiferromagnetic Textures

TL;DR

This paper demonstrates that antiferromagnets exhibit intrinsic magnetization when their order parameter varies spatially, influencing their dynamics and enabling control of domain walls with external magnetic fields.

Contribution

The study derives the continuum free energy of AFMs from the Heisenberg model, clarifies the physical meaning of continuum fields, and shows how intrinsic magnetization affects domain wall motion.

Findings

Intrinsic magnetization exists in AFMs with spatially varying order parameter.

External magnetic fields can move and control AFM domain walls.

The interpretation of continuum fields depends on the parametrization method.

Abstract

Antiferromagnets (AFMs) exhibit intrinsic magnetization when the order parameter spatially varies. This intrinsic spin is present even at equilibrium and can be interpreted as a twisting of the homogeneous AFM into a state with a finite spin. Because magnetic moments couple directly to external magnetic fields, the intrinsic magnetization can alter the dynamics of antiferromagnetic textures under such influence. Starting from the discrete Heisenberg model, we derive the continuum limit of the free energy of AFMs in the exchange approximation and explicitly rederive that the spatial variation of the antiferromagnetic order parameter is associated with an intrinsic magnetization density. We calculate the magnetization profile of a domain wall and discuss how the intrinsic magnetization reacts to external forces. We show conclusively, both analytically and numerically, that a spatially inhomogeneous magnetic field can move and control the position of domain walls in AFMs. By comparing our model to a commonly used alternative parametrization procedure for the continuum fields, we show that the physical interpretations of these fields depend critically on the choice of parametrization procedure for the discrete-to-continuous transition. This can explain why a significant amount of recent studies of the dynamics of AFMs, including effective models that describe the motion of antiferromagnetic domain walls, have neglected the intrinsic spin of the textured order parameter.