MEAN-FIELD RENORMALIZATION-GROUP - APPROACH TO THE DILUTED SITE-BOND-CORRELATED ISING-MODEL

We study the diluted site-bond-correlated (SBC) Ising model within the scheme of the mean-field renormalization group. The SBC Ising model h as been proposed to describe the phase diagram for KNipMg1-pF3. One tr eats the square (Z = 4) and simple cubic (Z = 6) lattices by using two different exchange interactions (denoted by models A and B). In the p resent paper, the phase diagram for some values of the correlation par ameter a, which range from zero to unity, is studied. We obtain two cr itical concentrations p(c)(alpha = 0) and p(c)(alpha not-equal 0) in a greement with results from Monte Carlo methods. In addition, an intere sting universal relation between the initial slope DELTA(mu)(alpha = 1 ) and DELTA(mu)(alpha = 0) is obtained (mu denotes model A or B). From this relation, we can estimate the possible exact values to the initi al slope on the completely correlated case. Our approach is valid for lattices with any coordination number Z.