Interface vacancy relocation model for annealing effect on exchange coupling between ferro-antiferromagnetic layers in NiFe/FeMn polycrystalline layer system

Annealing effect was inverstigated by using a sandwich NiFe/FeMn/NiFe sample. The sample was annealed at 70 C up to 90 h. It was found that both the coercivity and the exchange bias field of the two NiFe layers were increased with increasing the annealing time. An interface vacancy relocation mechanism is proposed to explain the experimental data. The proposed mechanism also explains the existence of the exchange bias field of a sample deposited at room temperature without field cooling as well as other related phenomena. The activation energy of about 1 eV obtained from the annealing time dependence of the switching field for both top and bottom NiFe layers suggests a mechanism in which a single activation process dominates, which is consistent with the new model. (C) 2002 Elsevier Science B.V. All rights reserved.