Exchange Anisotropy—A Review

Exchange anisotropy describes a magnetic interaction across the interface between two magnetic materials. A shifted hysteresis loop, sinθ torque curve, and rotational hysteresis in magnetic fields greater than 2K / Ms may result from this interaction if one of the materials is antiferromagnetic. This interaction has been found to exist between ferro-antiferromagnetic materials, ferri-antiferromagnetic materials, and ferri-ferromagnetic materials. The work of various people is discussed in terms of the expected behavior in these exchange coupled systems. Some interesting results of the exchange interaction are reviewed. These include improved properties of fine particle magnets, a memory effect in a mixed ferrimagnetic spinel, a rotatable anisotropy in thin films, and an explanation for the reverse magnetization of a deposit in the earth's crust. The interfacial conditions necessary to obtain the interaction between the two magnetic systems are discussed, and it is shown that they are met in several cases. Models are presented which yield rotational hysteresis in magnetic fields greater than 2K / Ms as has been found in all of the exchange coupled systems.