Phase diagram of the antiferromagnetic triangular Ising model with anisotropic interactions

It is argued that there exist two antiferromagnetic phases in the triangular Ising model with anisotropic interactions. A method due to Müller-Hartmann and Zittartz (MZ) is used to derive a closed-form expression for the phase boundary. We also give a criterion under which the MZ method is expected to be applicable and accurate.Work supported in part by a grant from the National Science Foundation.