A mixed spin-1/2 and spin-3/2 transverse Ising model with random bond is studies within the framework of the finite cluster approximation (FCA).The phase diagrams and the other critical properties are examined.Re entrant phenomenon which comes from the frustration of exchange interaction is found.
The two dimensional mixed spin system consisting of spin-1/2 and spin-1 with four-spin interactions exhibits tricritical behaviour. The influence of a transverse field on this behaviour is studied with the finite cluster approximation based on a single-site cluster theory. The state equations are derived for the square lattice. It has been shown that the system keeps its tricritical behaviour, but when the strength of the transverse field approaches a critical value, all transitions become of second-order for any value of four-spin interaction.
In the light of the effective-field theory, the present paper attempts to discuss the investigation done into the phase diagrams of a random nearest-neighbour interaction spin-1 Ising model with a single-ion anisotropy in an applied transverse field on the honeycomb lattice. The interactions are assumed to be independent random variables with distribution P(J ij )=p delta (J ij -J 1 )+(1-p) delta (J ij -J 2 ), where J 1 >0and mod J 2 /J 1 mod <or=1. We find a number of interesting phenomena, such as two different types of re-entrant phenomenon due to the competition between the random bond and the negative single-ion anisotropy parameter, as well as the usual frustration of J ij . The influence of a transverse field on the behaviours of the tricritical point and re-entrant transition is also discussed in this paper.