Anisotropy of crystalline ferromagnets with defects

This letter describes a model of the anisotropy of crystalline ferromagnetic alloys containing defect clusters. The focus is on ⟨100⟩-type pairs in bcc lattices each of which is assigned a uniaxial anisotropy of fixed magnitude. The lattice is also characterized by a coherent anisotropy energy due to the transition element host lattice as well as an isotropic exchange and magnetic dipole energy. This model is applied to a study of the concentration dependence of the fourfold magnetic anisotropy Keff(C) of quenched bcc Fe1−CGaC alloys. It yields Keff(C)∝1−κC4 which gives a good account of the dependence of Keff on C. In particular, it accounts for the collapse of Keff at C≈0.2, provided the magnitude of the local anisotropy energy is three orders of magnitude larger than that of the coherent fourfold anisotropy energy.