CRITICAL-BEHAVIOR OF THE 3-DIMENSIONAL ISING-MODEL WITH NEAREST-NEIGHBOR, NEXT-NEAREST-NEIGHBOR, AND PLAQUETTE INTERACTIONS

The critical and multicritical behavior of the simple cubic Ising mode l with nearest-neighbor, next-nearest-neighbor, and plaquette interact ions is studied using the cube and star-cube approximations of the clu ster variation method and the recently proposed cluster variation-Pade approximant method. Particular attention is paid to the line of criti cal end points of the ferromagnetic-paramagnetic phase transition: its (multi)critical exponents are calculated, and their values suggest th at the transition belongs to a different universality class. A rough e stimate of the crossover exponent is also given.