Magnetic Dipolar Interactions in MnO and in Ferrites

The magnetic dipole energies of MnO and of the normal and inverse spinel structures are calculated. It is found that with this interaction alone MnO would have its direction of spin alignment in a (111) plane, in contrast to the experimentally found [100]. The addition of a nearest neighbor quadrupole interaction is suggested as a means of making the [100] direction preferred. The normal and the inverse spinel structures are found to have zero magnetic dipole energies.