Interface and Volume Anisotropy

It has been shown[18] that in multilayers the effective magnetic anisotropy energy, $K_{ef}$, can be phenomenologically split into two components: a volume contribution, $K_{V}$, and an interface contribution, $K_{S}$, which are related to $K_{ef}$ by

$$K_{ef} = K_{V} + \frac{2K_{S}}{t}$$ (5.2)

where $t$ is the thickness of the magnetic layer. The relation is a weighted average of the magnetic anisotropy energy of the interface atoms and the inner ``volume'' atoms in the layer. The factor of 2 arises from the layer being bounded by two interfaces.

In bulk systems the magnetocrystalline anisotropy of a system is dominated by the volume term. In thin films and multilayers, however, the surface term can become more significant as $t$ becomes small ( $\sim\nicefrac{2K_{S}}{K_{V}}$). In most cases the anisotropy in thin magnetic layers is dominated by the dipolar shape anisotropy, favouring inplane moment alignment.