PHASE-TRANSITIONS IN THE SPIN-3/2 BLUME-EMERY-GRIFFITHS MODEL

The spin-3/2 Ising model on the square lattice with nearest-neighbor ferromagnetic exchange interactions (both bilinear (J) and biquadratic (K)) and crystal-field interaction (DELTA) is studied using a renormalization-group transformation in position-space based on the Migdal-Kadanoff recursion relations. The global phase diagram in (J, K, DELTA) space (with J, K greater-than-or-equal-to 0) is found to have two surfaces of critical phase transitions and two surfaces of first-order phase transitions. These surfaces are variously bounded by an ordinary tricritical line, an isolated critical line of end points, and a line of multicritical points. The global connectivity and local exponents of the thirteen separate fixed points underlying this quite complicated structure are determined.