Induced anisotropies in exchange-coupled systems on rippled substrates

Abstract

The role of monoatomic steps at the mutual interface between a ferromagnetic and an antiferromagnetic layer in a ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}∕{\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ exchange bias system is enlightened. For this purpose a special ripple substrate with a well defined morphology is used. Due to the film morphology a strong uniaxial anisotropy is induced in the polycrystalline ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ 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 the magnitude of the unidirectional anisotropy contribution scales with the step density of the substrate, which is in full agreement with theoretical predictions.