The magnetostatic energy associated with a polycrystalline ferrite

At the grain boundaries of moderately hard magnetic ferrites there occurs a layer of free pole of r.m.s. surface density ω̄. The magnitude of ω̄ is here estimated as a function of the over-all magnetization, and the magnetostatic energy of a grain in a demagnetized assembly is then found by calculating the energy of a spherical grain carrying free pole ± ω̄ 0 on alternate octants; the μ * effect, the presence of domain walls and the influence of surrounding grains are also considered. The value so found is consistent with that deduced from observation of domain wall spacings in manganese-magnesium ferrite.