HIGH-TEMPERATURE SERIES ANALYSES OF THE CLASSICAL HEISENBERG AND XY MODELS

Although there is now a good measure of agreement between Monte Carlo and bigh-temperature series expansion estimates for Ising (n = 1) models, published results for the critical temperature from series expansions up to 12th order for the three-dimensional classical Heisenberg (n = 3) and XY (n = 2) models do not agree very well with recent high-precision Monte Carlo estimates. In order to clarify this discrepancy we have analyzed extended high-temperature series expansions of the susceptibility, the second correlation moment, and the second field derivative of the susceptibility, which have been derived a few years ago by Luscher and Weisz for general O(n) vector spin models on D-dimensional hypercubic lattices up to 14th order in K-J/k(B)T. By analyzing these series expansions in three dimensions with two different methods that allow for confluent correction terms, we obtain good agreement with the standard field theory exponent estimates and with the critical temperature estimates from the new high-precision Monte Carlo simulations. Furthermore, for the Heisenberg model we also reanalyze existing series for the susceptibility on the BCC lattice up to 11th order and on the FCC lattice up to 12th order using the same methods.