RANDOM MIXED SPINS ISING-MODEL ON THE HONEYCOMB LATTICE

The Ising model on the honeycomb lattice with spins of magnitudes 1/2 and a with random exchange constant and random uniaxial anisotropy is considered. The two cases are studied separately, and in both cases bi nary annealed distributions of the random parameters are considered. A n exact solution is obtained by mapping the model onto the uniform spi n 1/2 Ising model on the triangular lattice, and the transition temper ature is determined as a function of the parameters for arbitrary a. E xplicit results are presented for s = 1 and s = 3/2, and it is shown t hat some critical parameters, surprisingly, are not universal.