Mechanisms of linear control of exchange bias in Fe/FeO bilayer

The microscopic nature of pinning uncompensated moment interface, how it is pinned by an antiferromagnet, and how the mechanism with this coupling drives exchange bias remain outstanding challenges. In this work, the Fe/FeO ferromagnet/antiferromagnet bilayer with an ultrathin FeO layer is modeled and the correlation between exchange bias and microscopically uncompensated antiferromagnetic magnetization is studied, based on first-principles calculations and modified Monte-Carlo simulations, where spin energies are exactly calculated and energy barriers are detectable to avoid the occurrence of unphysical tunneling during spin reversals. The linear dependence of exchange bias on uncompensated antiferromagnetic magnetization in Fe/FeO bilayer experimentally is reproduced and interpreted by exploring the monolayer-resolved magnetization behavior in the FeO layer, which depends on antiferromagnetic anisotropy, cooling field, fraction of Fe atoms permeated in the FeO layer, and magnetic frustration effect. It is evidenced that this linear dependence requires plenty of controllable pinning uncompensated antiferromagnetic spins located in the layer depths close to but not in contact with the ferromagnetic layer.