CRITICAL PROPERTIES OF THE SPIN-1 ASHKIN-TELLER MODEL FROM THE DIFFERENTIAL OPERATOR METHOD

In order to study the effect of the anisotropy parameter on the two co upled Ising models, we propose an Ashkin-Teller model (ATM) with spin variable S=1. Using an effective-field theory, We show that near the p artially ordered phase PO1 that appears in spin-1/2 ATM, this model pr esents a new partially ordered phase PO2. The anisotropy parameter int roduces a first-order phase transition between different phases. Howev er, the model exhibits a rich variety of phase diagrams and higher-ord er critical points.