LAUSR

Using Monte Carlo simulations, we study the critical behavior of two models of frustrated XY antiferromagnets with a collinear spin ordering and with an additional twofold degeneracy of the ground state. We consider a classic antiferromagnet on a body-centered cubic lattice with an additional antiferromagnetic exchange interaction between next-nearest spins, and a ferromagnet with an extra antiferromagnetic intralayer exchange. In both models, a single first-order transition in the discrete and continuous order parameters is found. Observed critical pseudo-exponents are in agreement with exponents of XYmagnets with a planar spin ordering like a stacked-triangular antiferromagnet and helimagnets belonging to the same symmetry class. A possible explanation of the pseudo-scaling behavior is also discussed.