Interface Coupling Transition in a Thin Epitaxial Antiferromagnetic Film Interacting with a Ferromagnetic Substrate

We report experimental evidence for a transition in the interface coupling between an antiferromagnetic film and a ferromagnetic substrate. The transition is observed in a thin epitaxial NiO film grown on top of Fe(001) as the film thickness is increased. Photoemission electron microscopy excited with linearly polarized x rays shows that the NiO film is antiferromagnetic at room temperature with in-plane uniaxial magnetic anisotropy. The anisotropy axis is perpendicular to the Fe substrate magnetization when the NiO thickness is less than about 15A° , but rapidly becomes parallel to the Fe magnetization for a NiO coverage higher than 25 A°