  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.
