Origin of Magnetic Anisotropy in CoxFe3−xO4

A model is proposed to explain the large part of the ferromagnetic anisotropy energy of CoxFe3−xO4(where x is small) which is caused by the presence of Co2+. The residual orbital angular momentum α(∼) of Co2+ is constrained by the crystal field to lie parallel to the axis of threefold symmetry. Spin-oribt energy λL·S couples the spin to this axis, accounting for the anisotropy energy. By fitting the theory to experimental anisotropy data, one finds that |αλ| = 132 cm−1. The assumption that cations are mobile at higher temperatures leads to an explanation of the anisotropy induced by magnetic annealing.