Detailed Magnetic Behavior of Nickel Near its Curie Point

Abstract

The temperature dependence of the initial susceptibility ${\ensuremath{\chi}}_{0}$ of nickel above the Curie point ${T}_{c}$ and the field dependence of its magnetization at ${T}_{c}$ are deduced from the data of Weiss and Forrer and found to be at variance with the simple molecular-field model. Instead, the experimental ${{\ensuremath{\chi}}_{0}}^{\ensuremath{-}1}$-versus-$T$ curve just above ${T}_{c}$ is shown to follow the simple relation ${{\ensuremath{\chi}}_{0}}^{\ensuremath{-}1}=A{(T\ensuremath{-}{T}_{c}]}^{\ensuremath{\gamma}}$, with $\ensuremath{\gamma}=1.35\ifmmode\pm\else\textpm\fi{}0.02$, in excellent agreement with the $\frac{4}{3}$-power relation recently predicted from the exact series for the Heisenberg model. From the coefficient $A$, it is deduced that ${\ensuremath{\mu}}_{0}$, the average atomic moment, is 0.642 ${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$ and that the individual electron moments are in a state corresponding to $S=\frac{1}{2}$. At higher temperatures, the ${{\ensuremath{\chi}}_{0}}^{\ensuremath{-}1}$-versus-$T$ curve deviates from the Heisenberg-model predictions, possibly because of a gradual rise in ${\ensuremath{\mu}}_{0}$ with increasing temperature. Up to the highest field $H$ of measurement, the magnetization at ${T}_{c}$ is shown to vary as ${H}^{\ensuremath{\epsilon}}$ with $\ensuremath{\epsilon}=0.237$, 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.