EXCHANGE AND LATTICE FRUSTRATION IN PRESENCE OF AN EXTERNAL MAGNETIC-FIELD

The planar triangular antiferromagnet shows a rich phase diagram in the H-T plane, the features of which have been enlighted via analytic low temperature expansion as well as Monte Carlo simulations. Three different phases with genuine nontrivial long range order in addition to the saturated ferromagnetic phase were found. Here it is shown that an analogous scenario is found in the square planar antiferromagnet with competing exchange interactions up to third nearest neighbors for exchange competition supporting a helix characterized by a wave vector Q = (2pi/3a, 0) at zero field.