NEEL TEMPERATURE AND SUBLATTICE MAGNETIZTION OF A 3-DIMENSIONAL CLASSICAL AND QUANTUM HEISENBERG-ANTIFERROMAGNET

The effective-field theory (EFT) of a two-spin cluster is applied to s tudy the critical behavior of a three-dimensional classical and quantu m Heisenberg antiferromagnet (AF). Neel temperature (T-N) and sublatti ce magnetization are calculated numerically and compared with the resu lts of these models with ferromagnetic (F) interaction. We find that o ur results, for the quantum model T-N is higher than T-c (Curie temper ature, F case) but for the classical model T-N = T-c. The difference b etween F and AF results for the quantum model obtained here by EFT is in accordance with Monte Carlo simulation and high-temperature expansi on. (C) 1998 Elsevier Science B.V. All rights reserved.