Semiclassical approach to the thermodynamics of spin chains

Using the PQSCHA semiclassical method, we evaluate thermodynamic quantities of one-dimensional Heisenberg ferro- and antiferromagnets. Since the PQSCHA reduces their evaluation to classical-like calculations, we take advantage of Fisher’s exact solution to get all results in an almost fully analytical way. Explicitly considered here are the specific heat, the correlations length and susceptibility. Good agreement with Monte Carlo simulations is found for S>1 antiferromagnets, showing that the relevance of the topological terms and of the Haldane gap is significant only for the lowest spin values and temperatures.