Deterministic domain selection of antiferromagnets via magnetic fields

TL;DR

This paper demonstrates that magnetic-field-driven switching of antiferromagnetic domains can be achieved through surface exchange reduction, highlighting the importance of surface spins and providing a new understanding of AFM responses to magnetic fields.

Contribution

It introduces a novel mechanism for deterministic AFM domain selection based on surface exchange asymmetry and susceptibility, supported by statistical mechanics and simulations.

Findings

Surface exchange asymmetry enables domain switching.

Enhanced surface spin susceptibility facilitates control.

Mechanism explains hysteresis in MnBi2Te4.

Abstract

Antiferromagnets (AFMs) hold promise for applications in digital logic. However, switching AFM domains is challenging, as magnetic fields do not couple to the bulk antiferromagnetic order parameter. Here we show that magnetic-field-driven switching of AFM domains can in many cases be enabled by a generic reduction of magnetic exchange at surfaces. We use statistical mechanics and Monte Carlo simulations to demonstrate that an inequivalence in magnetic exchange between top and bottom surface moments, combined with the enhanced magnetic susceptibility of surface spins, can enable deterministic selection of antiferromagnetic domains depending on the magnetic-field ramping direction. We further show that this mechanism provides a natural interpretation for experimental observations of hysteresis in magneto-optical response of the van der Waals AFM $\mathrm{MnBi_2Te_4}$. Our findings highlight the critical role of surface spins in responses of antiferromagnets to magnetic fields. Furthermore, our results suggest that antiferromagnetic domain selection via purely magnetic means may be a more common and experimentally accessible phenomenon than previously assumed.