Two-dimensional mixed spin Ising models with bond dilution and random ±J interactions

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Abstract

Using the finite cluster approximation we study a mixed spin model (spins Φ=1/2 andS=1) on a square lattice with nearest-neighbour and crystal field interactions. The nearest-neighbour couplingsK ij are assumed to be independent random variables with distribution,P(K ij )=pδ(K ij K)+(1−p)δ(K ij −αK), whereK>0. We investigate the cases α=0 and α=−1 corresponding to bond dilution and to random ±J interactions, respectively. In certain ranges ofp the phase diagrams exhibit tricritical behaviour and reentrance.

Supported by the agreement of cooperation between the DFG and the CNR-Maroc
On leave from Faculté des Sciences I, Université Hassan II, Casablanca, Morocco; and Laboratoire de Magnétisme Université de Rabat, Morocco