New Baxter phase in the Ashkin-Teller model on a cubic lattice

The mean field theory results are obtained from the Bogoliubov inequality for the spin-1/2 Ashkin-Teller model on a cubic lattice for different cluster sizes. The phase diagram, magnetization and free energy are obtained. From those expressions we observed a new phase in the model. Denoted in the course of this work by Baxter(2) this new phase presents 〈S〉≠〈σ〉≠0. The phase transitions between the Baxter(2) and the others well known phases for the model are studied and classified.