We investigate the nature of phase transitions in a generalized uniformly frustrated square-lattice model with XY spins. The frustration is made to vary by changing the negative bond strength η. From ground-state (GS) analysis we find that, below the critical value η=(1/3), the GS is ferromagnetic, while for η>(1/3), it is doubly degenerate with canted spin configurations. This suggests the existence of an Ising-like transition. This is confirmed by our extensive Monte Carlo simulations. In addition, there is a Kosterlitz-Thouless-like transition at higher temperature for η≠1. In the fully frustrated case (η=1), these two transitions are merged into a single one of dominant Ising character. These conclusions follow from a finite-size-scaling analysis and a visualization of the ordering.

• Received 12 July 1985

DOI:https://doi.org/10.1103/PhysRevB.34.3177