# Influence of strain and chemical substitution on the magnetic anisotropy of antiferromagnetic Cr$_2$O$_3$: an ab-initio study

## TL;DR

This study uses first-principles calculations to explore how strain and chemical substitutions influence the magnetic anisotropy energy in Cr$_2$O$_3$, revealing complex dependencies and potential ways to tune magnetic properties.

## Contribution

It provides a detailed ab-initio analysis of how strain and various chemical dopants affect the magnetic anisotropy in Cr$_2$O$_3$, highlighting mechanisms and potential for material tuning.

## Key findings

- Epitaxial strain significantly alters MAE by changing crystal-field splitting.
- Aluminum doping increases MAE through local lattice deformation.
- V and Nb dopants promote easy-plane anisotropy, affecting magnetic behavior.

## Abstract

The influence of the mechanical strain and chemical substitution on the magnetic anisotropy energy (MAE) of Cr$_2$O$_3$ is studied using first-principles calculations. Dzyaloshinskii-Moriya interaction contributes substantially to MAE by inducing spin canting when the antiferromagnetic order parameter is not aligned with the hexagonal axis. Nearly cubic crystal field results in a very small MAE in pure Cr$_2$O$_3$ at zero strain, which is incorrectly predicted to be negative (in-plane) on account of spin canting. The MAE is strongly modified by epitaxial strain, which tunes the crystal-field splitting of the $t_{2g}$ triplet. The contribution from magnetic dipolar interaction is very small at any strain. The effects of cation (Al, Ti, V, Co, Fe, Nb, Zr, Mo) and anion (B) substitutions on MAE are examined. Al increases MAE thanks to the local lattice deformation. In contrast, the electronic configuration of V and Nb strongly promotes easy-plane anisotropy, while other transition-metal dopants have only a moderate effect on MAE. Substitution of oxygen by boron, which has been reported to increase the N\'eel temperature, has a weak effect on MAE, whose sign depends on the charge state of B. The electric field applied along the (0001) axis has a weak second-order effect on the MAE.