Thermodynamical properties of the mixed spin transverse Ising model with four-spin interactions

The thermodynamical properties of the mixed spin transverse Ising system consisting of spin-1/2 and spin-1 with four-spin interactions are studied within the frame work of the finite cluster approximation based on single-site cluster theory. In this approach, the state equations are derived for the two-dimensional square lattice. In addition to the phase diagrams which show qualitatively interesting features (variety of transitions and tricritical behaviour), we find some characteristic behaviours of the longitudinal and transverse sublattice magnetizations. In particular, the gap of the longitudinal magnetization at first order transition decreases with increasing values of the transverse field. Moreover, the effects of the transverse field on the internal energy and the specific heat are also investigated.