C. Buzano et al., PHASE-TRANSITIONS IN A SPIN-1 MODEL WITH PLAQUETTE INTERACTION ON THESQUARE LATTICE, Physical review. B, Condensed matter, 53(22), 1996, pp. 15063-15070
An extension of the Blume-Emery-Griffiths model with a plaquette four-
spin interaction term, on the square lattice, is investigated by means
of the cluster variation method in the square approximation. The grou
nd state of the model, for negative plaquette interaction, exhibits se
veral new phases, including frustrated ones. At finite temperature we
obtain a quite rich phase diagram with two new phases, a ferrimagnetic
and a weakly ferromagnetic one, and several multicritical points.