Semiclassical approach to the thermodynamics of spin chains

Using the semiclassical method called pure-quantum self-consistent harmonic approximation (PQSCHA), we evaluate thermodynamic quantities of one-dimens ional Heisenberg ferromagnets and antiferromagnets, Since the PQSCHA reduce s their evaluation to classical-like calculations, we take advantage of Fis her's exact solution [M. E. Fisher, Am J. Phys. 32, 343 (1964)] to get all results in an almost fully analytical way. Explicitly considered here are t he specific heat, the correlation length, and the susceptibility. Good agre ement with available numerical data and Monte Carlo simulations is found fo r S > 1 ferromagnets and antiferromagnets; for the latter it is seen that t opological terms and the related Haldane gap are relevant only for the lowe st spin values and temperatures.