Magnetic-field-induced first-order transition in the frustratedXYmodel on a stacked triangular lattice

The results of extensive Monte Carlo simulations of magnetic-field-induced transitions in the XY model on a stacked triangular lattice with antiferromagnetic intraplane and ferromagnetic interplane interactions are discussed. A low-field transition from the paramagnetic to a three-state (Potts) phase is found to be very weakly first order with behavior suggesting tricriticality at zero field. In addition to clarifying some long-standing ambiguity concerning the nature of this Potts-like transition, the present work also serves to further our understanding of the critical behavior at ${\mathit{T}}_{\mathit{N}}$, about which there has been much controversy.