Effect of exchange coupling of polycrystalline antiferromagnetic layers on the magnetization behavior of soft magnetic layers

The complementary nature of the exchange bias field and the coercivity enhancement in ferromagnetic (F)-antiferromagnetic (AF) exchange-coupled layer systems is explained based on an extended Fulcomer and Charap's model, in which the directional distribution of the easy axes plays a decisive role in governing the magnetization behaviors. The model was further extended to deal with the AF-layer thickness ranging from zero to infinity taking into account of Neel's spin fanning model. A comprehensive explanation of the influence of exchange coupling on the magnetization behavior of the F-layer is given. It is shown that a rotational magnetization process is inherent for the samples in which the exchange coupling effect is dominant. The same model explains the temperature dependence of the exchange bias field and coercivity and the memory effect observed after annealing. The varieties of phenomena are mostly ascribed to the existence of distribution in the magnetic properties, net spin moment at the AF-grain surface and AF-grain size.