Origin of the Magnetic Anisotropy Energy of Cobalt Ferrite

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概要

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• The magnetic anisotropy of cobalt ferrite is considered to arise from the cobaltous ions in the crystalline field of a low symmetry. The crystalline field due to the averaged-out charge distribution of Co^<2+> and Fe^<3+> ions in the octahedral sites gives the lowest-lying twofold degenerate orbital level of the Co^<2+> ion and to this level are associated four spin levels, corresponding to S=3/2, as each spin is subject to exchange field. Each of these orbitally doubly degenerate levels is further split into two by the low symmetry field arising from the difference of charges of Co^<2+> and Fe^<3+> ions and spin-orbit coupling. The magnitude of this energy splitting depends on the direction of the exchange field, thus on the direction of the magnetization, and from this origin the anisotropy energy arises. The relation between the magnitude of the anisotropy energy and the strength of the low symmetry field is discussed. Two kinds of configuration, A and B, of the Co^<2+> and Fe^<3+> ions neighbouring each Co^<2+> ion are considered as having low energy values. By properly choosing the relative numbers of Co^<2+> ions in these A and B configurations and the strengths of the respective low symmetry fields, the calculated temperature dependence of the cubic anisotropy constant K_1 can be fitted with that measured by Shenker. The values of the parameters thus determined seem to be reasonable, as they can be compared with those calculated on the assumption of the point charge model. The magnetic moment consisting of the spin and orbital moments is calculated to be 3.4~3.5μ_B per Co^<2+> ion. Finally, the dependence of the anisotropy constant of the mixed Fe-Co ferrite on the concentration of the cobaltous ions is discussed.

• 一般社団法人日本物理学会の論文
• 1960-06-25

著者

• Tachiki Masashi

  Department Of Chemistry Faculty Of Science Osaka University:(present Address) The Research Institute

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