Establishing exchange bias below TN with polycrystalline Ni0.52Co0.48OCo 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, HE, below the AFM ordering temperature, TN. It was found that field-cooling the bilayers through TN provided very little, if any, increase in HE over that produced by deposition of the Co at temperatures far below TN. Further significant aspects of this issue were also examined. The biasing field, HB, needed to be applied only during the deposition of a small fraction (1nm) of the FM film below TN of the AFM to achieve the maximum HE; if HB was reversed at any time during the FM deposition, HE was determined by the final direction of HB; the direction of HE 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 HE.