Modelo de ising com spins mistos em um campo aleatório

Abstract

In this work, the ferromagnetic Ising model on the honeycomb lattice with mixed spins of magnitudes {1/2;1} and {1/2;3/2} in a random field is considered. Each set of spins occupies one of the two equivalent sub-lattices of the honeycomb lattice, and the random field is assumed to satisfy an annealed distribution. The model is exactly solved for symmetric field distributions by mapping the system onto the spin 1/2 Ising model on the triangular lattice. The solution is determined for constrained and unconstrained random field. It is also considered the effect of the uniaxial anisotropy in the critical behaviour of the system. The phase diagram is explicitly presented for the discrete field distributions where the field assumes the values o, ±h, with probabilities p and (l-pr./2 respectively, and it is shown that, for the constrained random field, there are non-universal critical probabilities Pc.