Abstract
The existence of a re-entrant ferromagnetic phase seems to be a general characteristic of systems with frustration and disorder even when no spin-glass phase exists. Using an effective field theory based on the use of a probability distribution that correctly accounts for the single site kinematic relations, a two-dimensional nearest-neighbour random interaction spin-3/2 Ising model is studied in which the interactions are independent random variables distributed according to the following law: P(J(ij) = p delta(J(ij) - J) + (1 - p) delta(J(ij) - alphaJ), where J > 0. In a certain range of negative values of alpha, re-entrant phase diagrams are found and the threshold p* at which the critical temperature goes to zero depends on alpha.