The exchange bias effect of epitaxial Ni_{81}Fe_{19}/Fe_{50}Mn_{50}-bilayers

One of the most striking features of the exchange coupling between a ferromagnetic and an antiferromagnetic material is the shift of the magnetization loop away from zero field. This exchange bias effect has received much attention in recent years because of its technological importance in magnetoresistive sensors and read heads as well as for magnetic random access memory. But still today more than forty years after the discovery of the effect, its microscopic origin has not yet been completely understood. As the exchange bias effect is an interfacial effect the structure of the interface between the two materials is of great importance. The magnetic properties of structurally well characterized epitaxial Ni_{81}Fe_{19}/Fe_{50}Mn_{50}-bilayers will be discussed in the framework of a modified Stoner-Wohlfarth model. Besides the unidirectional anisotropy describing the shift of the magnetization loop an induced four-fold anisotropy is found. The competing effects of these anisotropies can be analyzed by means of magnetic phase diagrams.