TRANSVERSE-RANDOM-FIELD MIXED ISING-MODEL WITH ARBITRARY SPINS

The transverse-random-field mixed Ising model consisting of arbitrary spin values has been studied by combining the pair model approximation with discretized path-integral representation. The phase diagrams of systems with mixed spins: sigma=1/2, S=1; sigma=1/2, S=3/2 and sigma=1 , S=2 are plotted. Not only the discontinuity at T=0 K is found betwee n the trimodal and bimodal distributions of transverse fields, which i s similar to the single-spin counterpart, but also the tricritical beh avior is observed in these phase diagrams when both transverse fields are trimodal distributed, which is different from the single-spin one. The appearance of tricritical point is independent of the coordinatio n number and spin values.