Exchange bias of antiferromagnetic/ferromagnetic bilayer with cubic anisotropy in antiferromagnetic layer

Disordered γ-phase antiferromagnetic Mn alloys bring about an exchange bias when the antiferromagnetic spin exhibits the triple Q spin structure. Since a certain amount of cubic anisotropy is possibly realized in the disordered γ-phase antiferromagnetic alloys, model calculations to determine the exchange bias in an antiferromagnetic (AFM)/ferromagnetic (FM) bilayer have been performed for the antiferromagnetic layer with a cubic anisotropy. The present calculations reveal that the formation of the interfacial domain wall in the antiferromagnetic layer predominates the exchange bias and that the critical cubic anisotropy D_C is defined by the domain wall width. In the torque curves calculated, as a function of the cubic anisotropy energy, a symmetric magnetic anisotropy curve in the ferromagnetic layer is clearly observed when no exchange bias field can be obtained. When a strong exchange bias is observed, on the other hand, the sinusoidal shape of the torque curve of the ferromagnetic layer disappears, showing a close relationship with the appearance of the exchange bias. From the present theoretical results, it is verified that the cubic anisotropy in the disordered AFM γ-phase alloys is closely associated with the exchange bias characteristics as well as the shape of torque curves of the AFM/FM bilayer.