Cluster Variation Method for Frustrated Magnets

Abstract

The model J₁-J₂ has provided a good theoretical benchmark for the study of frustrated magnets. This model is studied from the perspective of the Cluster Variation Method (CVM). In a first moment, Bethe approximation is considered. In this context it is possible to obtain a phase diagram where a stripes phase and a paramagnetic phase are observed, though separated by a non-convergence zone. Secondly, plaquette approximation is considered and a complete phase diagram is obtained. In the latter it is observed an additional nematic phase with orientational but not positional order, which was not possible to observe using the Bethe approximation.