Temperature-dependent magnetic interface location in interdiffused exchange biased bilayers

Abstract

Antiferromagnetic (AF) binary alloys are attractive choices for exchange pinning of ferromagnets (F) in applications. Unfortunately, inducing AF ordering in these alloys often requires annealing which leads to interdiffusion at the AF∕F interface and a subsequent, and poorly understood, reduction in exchange bias. We report a study of the effects of interdiffusion in epitaxial NiMn∕Ni bilayers. Using polarized neutron reflectometry, we deduce that the competition between AF and F interactions in the interdiffused region leads to a temperature-dependent magnetic interface location, “glassy” behavior, memory effects, and low-temperature training. The results have important implications for the understanding of the temperature dependence of the exchange bias in these materials.