ABSENCE OF THE PARTIALLY ORDERED PHASE IN THE Q-STATE MODELS .1. RENORMALIZATION-GROUP APPROACH

We investigate the q-state models called (N(alpha), N(beta)) model usi ng an infinitesimal Migdal-Kadanoff renormalization-group method. We d istinguish two cases namely the isotropic model and the anisotropic mo del. The first one presents a critical value of q, q(c) such that for q < q(c) we obtain an Ashkin-Teller phase diagrams while for q > q(c) the partially ordered phase disappears then the model exhibits only ph ase transition between ferromagnetic phase and disordered one. The pha se diagrams in the second case are qualitatively similar to one obtain ed for Z(6) model for all values of q.