A new effective field theory for spin-S (S<=1) dilute Ising ferromagnets

TL;DR

This paper introduces an improved effective-field theory for dilute spin-1/2 and spin-1 Ising models, analyzing phase transitions and critical concentrations with enhanced accuracy over previous methods.

Contribution

It develops a new effective-field approximation incorporating multi-site correlations and improved configurational averaging for dilute Ising models with transverse fields.

Findings

Critical concentration for phase transition determined

Dilution significantly alters characteristic features of the models

Conditions for reentrant phase transitions are complex and sensitive

Abstract

Site diluted spin-1/2 Ising and spin-1 Blume Capel (BC) models in the presence of transverse field interactions are examined by introducing an effective-field approximation that takes into account the multi-site correlations in the cluster of a considered lattice with an improved configurational averaging technique. The critical concentration below which the transition temperature reduces to zero is determined for both models, and the estimated values are compared with those obtained by the other methods in the literature. It is found that diluting the lattice sites by non magnetic atoms may cause some drastic changes on some of the characteristic features of the model. Particular attention has been paid on the global phase diagrams of a spin-1 BC model, and it has also been shown that the conditions for the occurrence of a second order reentrance in the system is rather complicated, since the existence or extinction of reentrance is rather sensitive to the competing effects between D/J, \Omega/J and c.