Antiferromagnetism of Zn-Ferrite

概要

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Assuming a reasonable magnetic superstructure of tetragonal symmetry, the magnetic anisotropy of Zn-ferrite is discussed. Magnetic moment carriers are Fe^<3+> ions in this substance. Therefore, the main source of the anisotropy energy is considered to be the magnetic dipole-dipole interaction between spins of Fe^<3+> ions, which gives the anisotropy energy depending upon the crystallographic orientation of the common axis of + and - spins below the Neel temperature, whereas above this temperature it does not give any anisotropy on account of the cubic structure of this crystal. The calculated anisotropy energy below the Neel temperature takes a minimum value when the direction of the magnetic moment lies in the plane perpendicular to the tetragonal c-axis. If the anisotropy h this plane is sufficiently small, the powder susceptibility would remain constant below the Neel temperature. This is supported by the experimental result. Further, the short range order is introduced by a method somewhat like that used by Li. The behaviors of the susceptibility and the specific heat near the Neel temperature are investigated by this method. The effect of the short range order on the susceptibility is shown to be considerably remarkable, but the constancy of the perpendicular susceptibility with respect to temperature is expected to remain almost unchanged.
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