Origin of Magnetic Anisotropy in CoxFe3−xO4

Abstract

A model is proposed to explain the large part of the ferromagnetic anisotropy energy of Co_xFe_3−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.