Asymmetric magnetization reversal in ferromagnetic/antiferromagnetic bilayers

The asymmetric magnetization reversal in exchange-biased ferromagnetic (FM)/ antiferromagnetic (AFM) bilayers is studied by the Monte Carlo method. Based on the calculations for both the random and regular configurations of dilution in the AFM layer, it is revealed that the asymmetry is closely related to the domain structure in the AFM layer. The coherent rotation of the magnetization in the FM layer is proven to be the dominant process for the appearance of the asymmetric magnetization reversal. A set of hysteresis loops is obtained for various angles between the external field and the anisotropic direction and for different thicknesses of the FM layer. The numerical results are in good agreement with the recent experimental measurements. In addition, the temperature dependence of the asymmetry is also studied. For a given angle, there is a maximum asymmetry at a certain temperature. Our results indicate that the asymmetry uniquely originates from the unidirectional anisotropy, and its magnitude is determined by the competition between the unidirectional anisotropy and the uniaxial anisotropy.