Ferromagnetic-antiferromagnetic coupling: NiFe thin films deposited on monocrystalline CoO substrates

NiFe thin films have been deposited on monocrystalline CoO substrates cut out from a single crystal and carefully polished. A loop displacement and a large increase of the easy axis coercive force are found below the Néel temperature of the oxide. At the same time, the torque curves show residual rotational hysteresis in large applied fields, unidirectional anisotropy and an anomalous increase of the uniaxial anisotropy. The results do not depend on the orientation, (111) or (100), of the substrates, because of surface roughness. Unidirectional anisotropy and rotational hysteresis are due to exchange coupling at the interface between the two materials. The increase inK_u andH_c might result from strain effects or from ferro-antiferromagnetic exchange coupling.Supported by DGRST, Contract No 69-01-908, and by CNRS.The authors wish to thank M. Schlenker and R. Perrier de in bâthie for supplying the CoO single crystals and for helpful discussions, J. L. Fraimbault for his valuable advices in the preparation of samples and N. Vejllet for her help in the mechanical polishing.