# Atomic antiferromagnetic domain wall propagation beyond the relativistic limit

## TL;DR

This paper explores atomic-scale antiferromagnetic domain wall dynamics driven by spin-orbit fields, revealing mechanisms for overcoming the relativistic speed limit through spin-wave emission and atomic-scale effects.

## Contribution

It introduces an energy conversion theory to explain domain wall motion beyond the relativistic limit, accounting for atomic-scale effects and spin-wave emission.

## Key findings

- Atomic domain walls exhibit Peierls-like pinning effects.
- Spin-orbit fields can induce fast, step-wise DW propagation.
- DW velocity can surpass the magnonic barrier through spin-wave emission.

## Abstract

We theoretically investigate the dynamics of atomic domain walls (DWs) in antiferromagnets driven by a spin-orbit field. For a DW with the width of a few lattice constants, we identify a Peierls-like pinning effect, with the depinning field exponentially decaying with the DW width, so that a spin-orbit field moderately larger than the threshold can drive the propagation of an atomic DW in a step-wise manner. For a broad DW, the Peierls pinning is negligibly small. However, the external spin-orbit field can induce a fast DW propagation, accompanied by a significant shrinking of its width down to atomic scales. Before stepping into the pinning region, noticeable spin waves are emitted at the tail of the DW. The spin-wave emission event not only broadens the effective width of the DW, but also pushes the DW velocity over the magnonic barrier, which is generally believed to be the relativistic limit of the DW speed. While the existing dynamic theory based on the continuum approximation fails in the atomic scale, we develop an energy conversion theory to interpret the DW dynamics beyond the relativistic limit.