Exchange anisotropy: phenomenological description and a simple model

Abstract

One of the key components in GMR materials , magnetic tunnel junctions or other electromagnetic devices is often an antiferromagnetic (AF) layer which is exchangecoupled to a ferromagnetic (F) layer. The function of the AF layer is to pin the magnetization direction of the adjacent F layer to a certain direction. The most prominent manifestation of the F/AF exchange interaction is a shift of the hysteresis loop of the F layer along the field axis, as if an additional fixed external field is applied to the F layer. This effective magnetic field is called the exchange bias field, H. The direction of this effective field is called the exchange bias direction. In contrast to the ferromagnetocrystalline anisotropy of a homogeneous magnet, which is characterized by easy and hard axes, exchange anisotropy is characterized by a single easy direction. It is called uniaxial anisotropy.