Monte Carlo study of O(3) antiferromagnetic models in three dimensions.

We study three antiferromagnetic formulations of the O(3) spin model in three dimensions by means of Monte Carlo simulations: (1) a two parameter s model with nearest- and next-nearest neighbors couplings in a cubic lattice; (2) a face-centered-cubic lattice with nearest-neighbor interaction; (3) a cubic lattice with a set of fully frustrating couplings. We discuss in all cases the vacua properties and analyze the phase transitions. Using finite-size scaling analysis we conclude that all phase transitions found are of first order.