(11) |

where is the demagnetization tensor, is the demagnetization field and is the magnetization of the system. Thus the density magnetostatic energy can be described as:

(12) |

If the semiaxes a, b, and c of the ellipsoid represent the axes of the coordination system the is a diagonal tensor. An arbitrary direction of the magnetization with respect to the semiaxes can be characterized by the direction cosine , , and . The tensor is given by:

(13) |

and the magnetostatic energy density can be written as:

(14) |

For thin films, magnetostatic interaction leads to an additional anisotropy favoring the in-plane anisotropy. In the case of elongated nanoparticles, magnetostatic interactions produce an additional easy axis parallel to the long dimensions.

Rocio Yanes