Angular dependence and phase diagrams of exchange-coupled epitaxial Ni₈₁Fe₁₉/Fe₅₀Mn₅₀(001) bilayers

The exchange bias effect, especially the angular dependence of the exchange bias field and the coercivity of the epitaxial Ni₈₁Fe₁₉/Fe₅₀Mn₅₀ bilayer system is investigated. In order to prepare a well defined layer sequence large emphasis is laid on the structural characterization of each layer. Low-energy electron diffraction and scanning tunneling microscopy are employed after each deposition step and the height-height-correlation function is analyzed to quantify the interface quality. Successively the angular dependence of the longitudinal and transverse magnetic component is investigated by magneto-optic Kerr effect magnetometry. In order to fully analyze the magnetization reversal behavior a special gray scale representation of the data is chosen. Theoretical results based on a modified Stoner-Wohlfarth model, which includes unidirectional and fourfold anisotropy contributions, are presented and compared to the experimental results. Although a homogeneous rotation of the magnetization is assumed the agreement between theory and experiment is surprisingly good. Only in a narrow angular range, where an ongoing rotation of the magnetization is predicted by the Stoner-Wohlfarth theory, discrepancies arise. The angular dependence of the possible orientations of the magnetization are summarized in a phase diagram.