Exchange bias of polycrystalline antiferromagnets with perfectly compensated interfaces

A mechanism for exchange bias and training for antiferromagnet/ferromagnet bilayers with fully compensated interfaces is proposed. In this model, the bias shift and coercivity are controlled by domain-wall formation between exchange-coupled grains in the antiferromagnet. A finite element micromagnetic calculation is used to show that a weak exchange interaction between randomly oriented antiferromagnetic grains and spin-flop coupling at a perfectly compensated interface are sufficient to create shifted hysteresis loops characteristic of exchange bias. Unlike previous partial wall models, the energy associated with the unidirectional anisotropy is stored in lateral domain walls located between antiferromagnetic grains. We also show that the mechanism leads naturally to a training effect during magnetization loop cycling.