Induced anisotropies in exchange coupled systems on rippled substrates

The role of monoatomic steps at the mutual interface between a ferromagnetic and an antiferromagnetic layer in a Ni81Fe19/Fe50Mn50 exchange bias system is enlightened. As a result of the reduced coordination at the step edges a strong uniaxial anisotropy is induced in the polycrystalline Ni81Fe19 layer, which is fixed in its orientation. By means of different field annealing cycles the direction of the induced unidirectional anisotropy can be chosen. For all mutual orientations both anisotropy contributions are superimposed independently and the angular dependence of the magnetization reversal behavior can be described perfectly by a coherent rotation model with one parameter set. In addition it is demonstrated that not only the magnitude of the uniaxial anisotropy contribution but also that of the unidirectional one scales with the step density of the substrate, which is in full agreement with theoretical predictions.