Giant magnetic anisotropy of the bulk antiferromagnets IrMn and IrMn3 from first principles

Abstract

We perform an ab initio study of the ordered phases of IrMn and IrMn3, the most widely used industrial antiferromagnets. Calculation of the form and the strength of the magnetic anisotropy allows the construction of an effective spin model, which is tested against experimental measurements regarding the magnetic ground state and the Néel temperature. Our most challenging result is the extremely strong second-order anisotropy for IrMn3 appearing in its frustrated triangular magnetic ground state, which is surprising since the ordered L12 phase has a cubic symmetry. We explain this large anisotropy by the fact that cubic symmetry is locally broken for each of the three Mn sublattices.