Antiferromagnetic thickness dependence of blocking temperature in exchange coupled polycrystalline ferromagnet/antiferromagnet bilayers

The exchange bias between an antiferromagnet (AF) and a ferromagnet (FM) vanishes at a temperature called the “blocking” temperature. Measurements are presented that show that the blocking temperature decreases with decreasing the thickness of the AF. This behavior is explained on the basis of a thermal fluctuation model, from which an analytic expression for the blocking temperature as a function of the antiferromagnetic thickness is obtained. This study also gives a quantitative understanding of the relationship between the blocking temperature and the AF grain size.