EXACT RESULTS OF THE MIXED-SPIN ISING MODEL ON A DECORATED SQUARE LATTICE WITH TWO DIFFERENT DECORATING SPINS OF INTEGER MAGNITUDES

Abstract

The mixed-spin Ising model on a decorated square lattice with two different decorating spins of integer magnitudes S B = 1 and S C = 2 placed on horizontal and vertical bonds of the lattice, respectively, is examined within an exact analytical approach based on the generalized decoration–iteration mapping transformation. Besides the ground-state analysis, finite-temperature properties of the system are investigated in detail. The most interesting numerical result to emerge from our study relates to a striking critical behavior of the spontaneously ordered "quasi-1D" spin system. It was found that this quite remarkable spontaneous order arises when one sublattice of the decorating spins (either S B or S C ) tends toward their "nonmagnetic" spin state S = 0, and the system becomes disordered only upon further single-ion anisotropy strengthening. In particular, the effect of single-ion anisotropy upon the temperature dependence of the total and sublattice magnetization is investigated.