Critical angles in angular dependent magnetization reversal of exchange biased Co/FeMn bilayers

Magnetization reversal behavior in the exchange biased Co/FeMn bilayers with collinearly aligned ferromagnetic (FM) intrinsic anisotropy and induced interfacial anisotropy was investigated by angular resolved magnetic hysteresis loops measurements, and special attention was paid to the magnetization signals recorded perpendicular to the external magnetic field direction (M y ). During the angular magnetization reversal process, two critical angles were clearly observed. Around the easy axis, the magnetization reverses in a full circle, i.e., two M y peaks appear with opposite signs. In contrast, above a certain critical angle α c1, the magnetization reverses only in one semicircle, i.e., M y always remains positive or negative. Above another critical angle α c2, the heights of the two M y peaks becomes equivalent. The angular dependence of exchange bias (ADEB) was also carefully investigated. In order to understand the experimental reversal behaviors clearly, numerical simulations were performed based on a modified Stoner-Wohlfarth (S-W) model considering the collinear anisotropies in current samples. The calculated results unambiguously show that the angular dependent reversal behavior as well as the occurrence of two critical angles is originated from the strength competition between the FM intrinsic anisotropy and the field cool induced interfacial exchange anisotropy.