Polarizing an antiferromagnet by optical engineering of the crystal field

TL;DR

This paper demonstrates that optical phonons can induce significant piezomagnetic effects in antiferromagnets, enabling rapid and large-scale control of magnetism without mechanical strain, with potential applications in spintronics.

Contribution

It introduces a novel method to reproduce piezomagnetism using optical phonons driven by light, surpassing traditional strain-based techniques in magnitude and speed.

Findings

Achieved a ferrimagnetic moment of 0.2 μB per unit cell.

Generated nearly three orders of magnitude larger effects than mechanical strain.

Demonstrated optical phonon-driven control of antiferromagnetic properties.

Abstract

Strain engineering is widely used to manipulate the electronic and magnetic properties of complex materials. An attractive route to control magnetism with strain is provided by the piezomagnetic effect, whereby the staggered spin structure of an antiferromagnet is decompensated by breaking the crystal field symmetry, which induces a ferrimagnetic polarization. Piezomagnetism is especially attractive because unlike magnetostriction it couples strain and magnetization at linear order, and allows for bi-directional control suitable for memory and spintronics applications. However, its use in functional devices has so far been hindered by the slow speed and large uniaxial strains required. Here, we show that the essential features of piezomagnetism can be reproduced with optical phonons alone, which can be driven by light to large amplitudes without changing the volume and hence beyond the elastic limits of the material. We exploit nonlinear, three-phonon mixing to induce the desired crystal field distortions in the antiferromagnet CoF$_2$. Through this effect, we generate a ferrimagnetic moment of 0.2 $\mu_B$ per unit cell, nearly three orders of magnitude larger than achieved with mechanical strain.