Field-induced effects in the S=1 two-dimensional Heisenberg antiferromagnet

We use the self-consistent harmonic approximation to study the spin S = 1 Heisenberg antiferromagnet on a two-dimensional lattice in a uniform applied magnetic field. The magnetic field destroys the O(3) symmetry and an XY-like behavior, with a Berezinskii-Kosterlitz-Thouless (BKT) transition, is expected. We obtain the field dependence of the transition temperature for fields varying in a wide range. There has been experimental evidence that, for low dimensional spin systems, a gap can be induced by the applied magnetic field. We also investigate the behavior of this field-induced gap.