A THEORETICAL-STUDY OF THE DILUTED SPIN-5 2 BLUME-CAPEL MODEL/

The quenched site-diluted spin-5/2 Blume-Capel model is studied using a new technique in effective field theory that employs a probability d istribution within the framework of single-site cluster theory based o n the use of exact Ising spin identities. The probability distribution , derived with the aid of Tucker's generalised Van der Waerden operato rs, correctly account for the single site kinematic relations and cert ain configurational averaging identities. The concentration dependence of the ferromagnetic phase boundary is studied. In particular, it is found that a range of single-ion field strengths exists over which the critical concentration for ordering varies anomalously. Results for t he honeycomb, square and cubic lattices are presented. The thermal var iation of the magnetization, the quadrupolar, and higher order magneti zation moments, are presented for selected values of the concentration .