Phase transitions in a triangular Blume-Capel antiferromagnet

Abstract

We study the critical behavior of a frustrated Blume-Capel (BC) antiferromagnet on a triangular lattice by Monte Carlo simulations. For a reduced single-ion anisotropy strength $\ensuremath{-}1.47\ensuremath{\lesssim}\ensuremath{\Delta}<0$, we find two phase transitions. The low-temperature phase is characterized by the antiferromagnetic long-range ordering (LRO) on two sublattices with the third one remaining in a nonmagnetic state. At higher temperatures, there is a critical region of the Berezinskii-Kosterlitz-Thouless (BKT) type with a power-law decaying spin-correlation function. For $\ensuremath{-}1.5\ensuremath{\le}\ensuremath{\Delta}\ensuremath{\lesssim}\ensuremath{-}1.47$, there is only one phase transition from the LRO to the paramagnetic region and the transition is of first order. The presence of the BKT phase in the current frustrated BC model is a new feature not observed in its nonfrustrated counterparts. The values of the decay exponent $\ensuremath{\eta}$ of the BKT phase corresponding to upper and lower temperatures appear to be consistent with the theoretical predictions for the six-state clock model.