Establishing exchange bias below T-N with polycrystalline Ni0.52Co0.48O/Co bilayers

Exchange-coupled bilayers of polycrystalline ferromagnetic (FM) Co on antiferromagnetic (AFM) Ni0.52Co0.48O were investigated with emphasis on the issue of establishing an exchange-bias field, H-E, below the AFM ordering temperature, T-N. It was found that field-cooling the bilayers through T-N provided very little, if any, increase in H-E over that produced by deposition of the Co at temperatures far below T-N. Further significant aspects of this issue were also examined. The biasing field, H-B, needed to be applied only during the deposition of a small fraction (1 nm) of the FM film below T-N of the AFM to achieve the maximum H-E; if H-B was reversed at any time during the FM deposition, H-E was determined by the final direction of H-B; the direction of H-E could be reversed after it had been established by applying a reversed field during a post-deposition latent period. These and other findings are considered with respect to clarification of the mechanisms for establishing H-E.