Enhanced finite size and interface mixing effects in Iridium Manganese ultra thin films

The finite size and temperature dependent properties of antiferromagnets are of critical importance to a wide range of spintronic and neuromorphic computing devices. Here we present atomistic simu- lations of IrMn, one of the most technologically important antiferromagnets, in both the ordered (L12) and disordered (γ) phases. We have found that antiferromagnetic IrMn3 films show a stronger finite size dependence of the Néel temperature than an equivalent ferromagnet due to the existence of spin frustration. We also find that the disordered γ-IrMn3 phase shows a dramatic reduction in the Néel temperature to less than room temperature for films less than 1 nm thick. Interfacial intermixing of the IrMn3 with a non-magnetic Cu capping layer further reduces the Néel temperature for a given film thickness, with a stronger influence on the disordered γ-IrMn3 phase compared to the ordered L12-IrMn3 phase. Our results suggest a larger antiferromagnetic film thickness is required for devices operating at or above room temperature compared to an equivalent ferromagnet, particularly for sputtered films with a high degree of interfacial intermixing.