Néel temperature and sublattice magnetiztion of a three-dimensional classical and quantum Heisenberg antiferromagnet11We would like to thank the CNPq and CAPES (Brazilian Agencies) for financial support.

The effective-field theory (EFT) of a two-spin cluster is applied to study the critical behavior of a three-dimensional classical and quantum Heisenberg antiferromagnet (AF). Néel temperature (TN) and sublattice magnetization are calculated numerically and compared with the results of these models with ferromagnetic (F) interaction. We find that our results, for the quantum model TN is higher than Tc (Curie temperature, F case) but for the classical model TN=Tc. The difference between F and AF results for the quantum model obtained here by EFT is in accordance with Monte Carlo simulation and high-temperature expansion.