Effect of antiferromagnet on exchange bias in systems with antiferromagnetic interfacial coupling and inverted ferromagnetic-antiferromagnetic core-matrix morphology.

A modified Monte Carlo Metropolis method is performed to simulate the effects of antiferromagnetic exchange interaction J(AF) and anisotropy K(AF) on exchange bias field H(E) and coercivity H(C) in the nanoparticle systems with antiferromagnetic interfacial coupling and inverted ferromagnetic-antiferromagnetic core-matrix morphology after cooling in weak and strong fields H(CF), respectively. The results show that the J(AF) dependence of H(E) is insensitive, except obvious changes occur at intermediate J(AF) for two H(CF). When the values of J(AF) are weak, the absolute values of H(E) may keep at a relatively large value. H(C) has a peak at approximately J(AF) = -0.6 with the increase of J(AF) for weak H(CF), while the opposite trend appears for the case of strong H(CF). H(E) is negative and its absolute value increases with the increase of K(AF) for weak H(CF), so does the trend of H(E) with K(AF) for strong H(CF) as K(AF) < or = 6. However, with further increase of K(AF) for strong H(CF), H(E) varies from the negative value to the positive value. Whereas H(C) for two values of H(CF) both decrease and finally level off with increasing K(AF). Variations of antiferromagnetic exchange interaction and anisotropy may alter the net magnetization and the pinning ability of spins on the surface of frustrated antiferromagnetic cores, resulting in the change of pinning configuration in the antiferromagnet during the magnetization reversal of ferromagnetic spins to influence the exchange bias.