A dictionary definition of anisotropy is ?a difference of property or of effect in different directions.? Magnetic anisotropy in materials is concerned with the observation that the magnetization prefers to point parallel or antiparallel to a particular direction or axis. A detailed treatment of the fundamentals of magnetic anisotropy is given by Chikazumi (1997).

Anisotropy can be related to the crystal structure of the material and, in the case of thin-film materials, to the form of the material, to the importance of the break of symmetry at the surfaces of the thin layer, to any strain in the thin film, to the morphology of the microstructural units making up the film, to any directional atomic ordering in the film, and to any other interface effects at the junction of overlaid films. It is clear that perpendicular anisotropy, i.e., anisotropy favoring an orientation of the magnetization normal to the plane of the film, is one of the most important materials requirements in MO recording technology.

To a sufficient approximation the effective anisotropy, K _EFF, can be written phenomenologically in terms of a volume term, K _V, and a surface term, K _S:

where t _F is the thickness of the magnetic element. K _V necessarily contains a magnetocrystalline anisotropy term, any stress term, any shape anisotropy term, any growth-induced anisotropy term, and any other volume sources of anisotropy. The demagnetizing energy for a film magnetized normal to its surface is also included as...