Expansions for Magnetization Characterization for Polycrystalline Orthorhombic and Cubic Magnetite at Low Temperatures

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Abstract
Taylor series expansions are obtained for the reduced magnetization and crystalline anisotropy energy which do not require that the magnetization vector lie in a plane formed by the easy axis and the applied field. The free energy which is assumed to be composed of magnetostatic and crystalline anisotropy energy is minimized with respect to the spherical coordinates of the magnetization vector. The expansions for the magnetization in terms of the crystalline anisotropy constants are used to find the mean magnetization at different magnetic field intensities for polycrystalline magnetite, which undergoes an order-disorder transition at -155°C. Experimental results for the magnetization of polycrystalline magnetite are compared with those predicted by the expansions and good agreement is observed.