THEORY OF ANISOTROPIC SPONTANEOUS MAGNETIZATION AND ANISOTROPY ENERGY IN ORTHORHOMBIC FERROMAGNETS AT 0 DEGREES K

A new mechanism of anisotropic spontaneous magnetization is proposed. It consists of the mutual admixture, due to perturbations caused by one-ion anisotropy, of appropriate eigenstates of the Hamiltonian describing the molecular field energy. A self-consistent method is developed in which the anticipated anisotropic part of the spontaneous magnetization contributes to the molecular field, and the direction of the spontaneous magnetization is fixed by an applied field. Using the quadratic parts of the one-ion spin Hamiltonian as the perturbation, the first- and second-order portions of the anisotropic spontaneous magnetization and anisotropy energy are calculated for an orthorhombic ferromagnet at 0°K. It is pointed out, however, that the present method applies to other perturbations also. The calculation shows, among other things, that higher-order perturbations do usually contribute to first-order anisotropy constants. This result is contrary to accepted conclusions contained in the literature. The predictions of the present theory are compared with those of others, and its possible generalizations and applicability to experiments are discussed. Finally, the first-order portion of the anisotropic spontaneous magnetization and anisotropy energy arising from an anisotropic g factor are calculated and compared to experimental data on gallium iron oxide. The full text of this paper will appear in The Physical Review. [Note added in proof: See, G. T. Rado, Phys. Rev. 176, 644 (1968).] © 1969 The American Institute of Physics.