J Appl Phys 95 (2004) 6807-6809
In order to study the effect of surface anisotropy, we have
developed a three-dimensional finite element micromagnetic
model. The finite element mesh of the particles is split into a
core region with bulk properties and a surface region (shell)
of variable thickness with modified material parameters. We
have studied the magnetization reversal in FePt nanoparticles.
The effect of surface anisotropy strongly reduces their
coercivity. An Fe-oxide shell with low anisotropy in the plane
of the surface has been considered as well as surface
anisotropy with high anisotropy constants and axis orientation
perpendicular to the surface.