MULTICRITICAL POINTS AND REENTRANT PHENOMENON IN THE BEG MODEL

The Blume-Emery-Griffiths model is investigated by use of the cluster variation method in the pair approximation. We determine the regions of the phase space where the reentrant phenomenon takes place. Two regions are found, depending on the sign of the reduced quadrupole-quadrupole coupling strength xi. For negative xi we find para-ferro-para and ferro-para-ferro-para transition sequences; for positive xi, a para -ferro-para, sequence. Order parameters, correlation functions and specific heat are given in some typical cases. By-products of this work are the equations for the critical and tricritical lines.