Dipolar Energy Anisotropy in Hexagonal Ferrites

Abstract
The dipolar energy contribution to the anisotropy of M-, W- and Y-type hexagonal ferrites is examined. The geometrical coefficients k_ij are given, so that a calculation for any hexaferrite with the same structure can be effected. Differences in the results of previous works are explained as due to a simplifying assumption, the validity of which is restricted. The ambiguity regarding dipolar energy anisotropy has been raised: dipolar energy anisotropy is dominant in BaZn-Y, while it is negligible in M- and W-type hexagonal ferrites. The results suggest that single ion anisotropy of the bipyramidal site is significant but the contribution of all the other sites is equally important.