Classification of Magnetic Forces on Antiferromagnetic Domain Wall

TL;DR

This paper classifies the magnetic forces acting on antiferromagnetic domain walls, revealing how tiny net magnetization and Neel order respond to field gradients, enabling rapid manipulation of AFM states with high-speed domain wall propagation.

Contribution

It provides a complete classification of magnetic forces on AFM domain walls, explaining their responses to inhomogeneous fields and proposing a method for fast AFM domain wall manipulation.

Findings

Tiny net magnetization responds to field gradient.

Neel order is sensitive to sublattice field differences.

Domain wall speed can reach tens of km/s, much faster than electric current-driven methods.

Abstract

A major challenge in spintronics is to find an efficient means to manipulate antiferromagnet (AFM) states, which are inert relative to a uniform magnetic field, due to the vanishingly-small net magnetization. The question is, how does an AFM response to an inhomogeneous field? Here we address the problem through a complete classification of the magnetic forces on an AFM domain wall (DW), revealing the following physical properties: (i) the tiny net magnetization still responses to the field gradient. (ii) the N\'{e}el order is sensitive to the field difference between two sublattices. (iii) DW energy has a quadratic dependence on the magnetic field due to its noncollinear structure. Remarkably, the first two factors drive DW to the opposite directions in a nanowire, but the third effect tends to push the DW to the high field region. Consequently, the competition among these three forces can be applied to understand the seemingly-contradictory results on AFM motion in literature. Additionally, our results provide a new route for a speedy manipulating AFM DW; our numerical simulation indicated that for a synthetic antiferromagnet, the DW propagating speed can reach tens of kilometers per second, an order of magnitude higher than that driven by an electric current.