Angular dependencies of exchange bias and coercivity in the ferromagnetic/antiferromagnetic bilayers not subjected to field-cooling treatments

We report a study of angular dependencies of exchange bias and coercivity at low temperature in the ferromagnetic/antiferromagnetic bilayers not subjected to field-cooling treatments, based on modified Monte Carlo simulations. Line symmetries about the easy axes for the angular dependencies of exchange bias and coercivity and central symmetry about the hard axes for the angular dependent exchange bias are observed simultaneously. Exchange bias field in the bilayers with strong antiferromagnetic anisotropy is positive for the initial magnetizing and around the hard axes changes its sign from negative to positive. Opposite trends are obtained for the case of weak antiferromagnetic anisotropy. The results are interpreted by means of magnetization reversal mechanisms and microscopic spin configurations. Strong antiferromagnetic anisotropy elevates the energy barriers to trap the antiferromagnetic spins in metastable states and results in a large size of domains and limited domain walls. The angular dependencies of exchange bias and coercivity therefore become asymmetric and exhibit complex behaviors.