Re‐Entrant Ferromagnetism in a Two‐Dimensional Spin‐3/2 Ising Model with Random Nearest‐Neighbour Interactions

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 indepcndent random variables distributed according to the following law: P ( J ij ) = p δ( J ij − J ) + ( 1 − p ) δ ( J ij − α J ), where J > 0. In a certain range of negative values of α, re‐entrant phase diagrams are found and the threshold p * at which the critical temperature goes to zero depends on α.