Ising model with two-spin interactions and three-spin interactions on a square lattice

Abstract

An investigation is given for an Ising model on a square lattice with two-spin interactions for all the vertical bonds and with three-spin interactions which exist alternately from triplets of three successive sites in a row of the horizontal direction and slantwise from row to row. We prove that there exists a phase transition in the system. An upper bound and a lower bound to the critical temperature are obtained. By using the finite-size scaling method, we calculate the thermal exponent and suggest that the system belongs to the same universality class as the Baxter-Wu model.