A two-dimensional Ising model with non-universal critical behaviour

Abstract

It is shown that the two-dimensional square lattice Ising model with the nearest-neighbour ferromagnetic interaction J, the next-nearest-neighbour antiferromagnetic interaction J' < 0 and the four-body interaction Jint shows non-universal critical behaviour when J is small. The estimations of critical temperature Tc and the critical exponent of susceptibility λ are performed within errors of 0.003% and 1.2%, respectively.