CoO1-δ layers in a reactively sputtered exchange-bias system

Abstract

In exchange-bias (EB) systems involving CoO as the antiferromagnetic (AF) component, preparation of overoxidized (i.e. CoO1+δ) AF layers has previously been shown to have an important effect on EB properties, which arises due to point defects associated with the nonstoichiometric material. Here, we present a study on the effect of post-deposition annealing to progressively higher temperatures, Tann, on magnetic and structural parameters of a [Co/CoO/Ag]30 multilayer. Our results indicate a different AF layer stoichiometry: CoO1-δ (i.e. underoxidized), with δ = 0.1 for the as-deposited sample. The annealing behaviour of the different parameters is explained via a mechanism of thermally induced diffusion of Co ions from the oxide to the Co layers, which is initiated at T ann ≈ 300°C (= T*) and leads to the approach to stoichiometry (i.e. Co1O1) in the AF layers. We suggest why our sample preparation conditions could have led to this unusual (i.e. CoO1-δ) stoichiometry and comment on possible future studies. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.