HIGH-TEMPERATURE SERIES EXPANSION OF THE SPIN CORRELATION-FUNCTIONS IN B-SPINEL LATTICE

High-temperature series expansion of the spin correlation functions on the B-spinel lattice are computed to order 6 in beta = 1/k(B)T for He isenberg model having both nearest- and next-nearest-neighbour exchang e integrals. The results are given for various neighbour correlations (up to the third). The behaviour with the temperature and the site dil ution is presented. The obtained results provide a useful tool for a s traightforward interpretation and understanding of experimental data T he approach is applied to the experimental results of the B-spinel ZnC r2xAl2-2xS4 in the dilution range 0.85 less than or equal to x less th an or equal to 1. The critical temperature and the critical exponents for the susceptibility and the correlation length are deduced by apply ing the Pade approximant methods.-The following estimates are obtained for the familiar critical exponents: nu = 0.691 +/- 0.011 and gamma = 1.382 +/- 0.012. These values are not sensitive to the dilution ratio x. The transition temperatures as a function of x obtained by the pre sent theory are found to be in excellent agreement with the experiment al ones.