CRITICAL-BEHAVIOR AND CRITICAL EXPONENTS IN ZNXCD1-XCR2SE4 COMPOUNDS ESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.45)

The spinel solid solutions ZnxCd1-xCr2Se4 have been studied by mean of macroscopic magnetization measurements in the range 0.35 less than or equal to x less than or equal to 0.45. The ferromagnetic scaling prop erties permit to determine the critical temperature T-C and the critic al exponents beta, gamma, and delta. Whereas the compounds with x = 0. 35 and 0.41 exhibit exponents compatible with a 3D Heisenberg ferromag netic model, a slight increase of beta, gamma, and a decrease of delta were found for x = 0.45. The Kadanoff scaling law gamma = beta(delta - 1) is satisfied by the experimental data. Using the mean-field theor y and the spin-wave theory at low temperatures, the exchange integrals were calculated up to the third nearest neighbours.