Free Energy of the Classical Heisenberg Model

Abstract

High-temperature power-series expansions for the free energy of a classical Heisenberg ferromagnet in an applied field are given in the form $\frac{-F}{\mathrm{NkT}}=\Sigma \stackrel{}{n,l}{a}_{2n,l}{h}^{2n}{x}^l,$ where $h=\frac{g\beta H}{kT}$ and $x=\frac{J}{kT}$. The coefficients are given for $l\le 7$ and $4\le 2n\le 10$. Estimates of the critical exponents for the fourth to tenth field derivatives of $F$ are given.