Detailed Magnetic Behavior of Nickel Near its Curie Point

The temperature dependence of the initial susceptibility χ₀ of nickel above the Curie point Tc and the field dependence of its magnetization at Tc are deduced from the data of Weiss and Forrer and found to be at variance with the simple molecular-field model. Instead, the experimental χ₀^-1-versus-T curve just above Tc is shown to follow the simple relation χ₀^-1=A(T-Tc]^γ, with γ=1.35±0.02, in excellent agreement with the 4/3-power relation recently predicted from the exact series for the Heisenberg model. From the coefficient A, it is deduced that μ₀, the average atomic moment, is 0.642 μB and that the individual electron moments are in a state corresponding to S=1/2. At higher temperatures, the χ₀^-1-versus-T curve deviates from the Heisenberg-model predictions, possibly because of a gradual rise in μ₀ with increasing temperature. Up to the highest field H of measurement, the magnetization at Tc is shown to vary as H^ε with ε=0.237, which is consistent with the exponent values for an analogous empirical relationship between the density and pressure of several different gases at their critical points.