# Extraordinary temperature dependent magnetic anisotropy of the non-collinear antiferromagnet IrMn

## TL;DR

This study investigates the temperature-dependent magnetic anisotropy in non-collinear antiferromagnet IrMn, revealing complex spin structures and their impact on thermal stability relevant for spintronic devices.

## Contribution

The paper introduces an atomistic spin model and Monte Carlo simulations to accurately determine the anisotropy energy surface of IrMn, resolving discrepancies between theory and experiment.

## Key findings

- Meta-stable spin structures significantly lower energy barriers.
- Anisotropy energy scales with temperature exponent close to 3.
- Non-collinear spins critically influence thermal stability.

## Abstract

The magnetic anisotropy of antiferromagnets plays a crucial role in stabilising the magnetisation of many spintronic devices. In non-collinear antiferromagnets such as IrMn the symmetry and temperature dependence of the effective anisotropy are poorly understood. Theoretical and experimental calculations of the effective anisotropy constant for IrMn differ by two orders of magnitude, while the symmetry has been calculated as uniaxial in contradiction to the assumed relationship between crystallographic symmetry and temperature dependence of the anisotropy from the Callen-Callen law. In this letter we determine the effective anisotropy energy surface of \Lonetwo - \IrMn using an atomistic spin model and constrained Monte Carlo simulations. We find that meta-stable spin structures lower the overall energy barrier to a tenth of that estimated from simple geometrical considerations, significantly reducing the discrepancy between experiment and theory. The temperature scaling of the anisotropy energy barrier shows an exponent of \factor, close to a uniaxial exponent of 3. Our results demonstrate the importance of non-collinear spin states on the thermal stability of antiferromagnets with consequences for the practical application of antiferromagnets in devices operating at elevated temperatures.