Determination of Molecular Field Coefficients in Ferrimagnets

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Abstract
An improved method is presented for determining those three molecular field coefficients which yield essentially the best agreement between the Néel theory and the experimental curve of saturation moment per unit mass (σ) versus temperature (T) in a given ferrimagnetic material. This method is analytical, and for a given accuracy it is more rapid than previously used trial‐and‐error methods. Experimental data on σ vs T are presented for monocrystals of lithium ferrite and two compositions of magnesium‐iron ferrite. One of the latter ferrites was measured in two states of ionic distribution which were obtained by varying the heat treatment. Application of the analytical method to these data shows that the agreement between the Néel theory and experiment is somewhat better than that expected on the basis of previous work. The present method is particularly useful for determining the temperature dependence of the sublattice magnetizations. Accurate values of these magnetizations are required, for example, in calculations of the temperature dependence of magnetocrystalline anisotropy by means of crystalline field theory.