Two-spin cluster theory applied to the ferromagnetic spinel CdCr2pIn2-2pS4

The magnetic properties of the B-spinel ferromagnetic CdCr2pIn2-2pS4 compou nd are studied via a cluster series expansion approximation with nearest an d next-nearest exchange integrals J(1) and J(2), respectively. Using the mi nimization of the free-energy expressions, the magnetization, the magnetic susceptibility, the two-spin correlation functions and the specific beat ar e obtained and computed numerically as a function of temperature and for ea ch composition of the system. The magnetization curves are used to determin e the critical temperatures T-c. Using the pow er la Ns in the vicinity of the critical regions the critical exponents beta,gamma and alpha associated . respectively, with the magnetization, the magnetic susceptibility and the specific heat are numerically calculated. The critical temperatures T-c ob tained are in very good agreement with those predicted by the magnetic meas urements and the values of the critical exponents may be compared with othe r theoretical results based on the 3D Heisenberg model. (C) 2001 Elsevier S cience B.V. All rights reserved.