General analysis of the complementary nature of coercivity enhancement and exchange bias in ferro-antiferromagnet (F-AF) exchange coupled systems

Complementary nature of coercivity enhancement and exchange bias is generalized from the layered systems to ferro-antiferromagnet (F-AF) exchange coupled systems with arbitrary configurations and is proved based on the coherent rotation of the F magnetization. In the proof, the effect of F-AF coupling is absorbed into the anisotropy of the F part, resulting in an arbitrary anisotropy for the F part. The proof starts from a general discussion on the initial susceptibility of a single domain particle. Then the fundamental correlation between the maximal initial susceptibility and the critical field along an arbitrary easy direction of a single domain particle, at which the magnetization becomes unstable, is discussed. Finally, the difference of the initial switching field and the actual switching field along the arbitrarily chosen easy direction is discussed.