Critical Properties of the Magnetically Disordered B-Spinel ZnxCd1xCr2Se4 (0.35 ≤ x ≤ 0.58)

Abstract

We study the critical behaviour of the B-spinel ZnxCd1–xCr2Se4 systems in the concentration range 0.35 ≤ x ≤ 0.58. Using the mean field theory and the ferromagnetic spin-wave theory at low temperatures, the exchange integrals were calculated up to the third nearest neighbours. The ferromagnetic critical region is studied by the high-temperature series expansion extrapolated with the Padé approximants method. The critical temperatures Tc and the critical exponents associated with the magnetic susceptibility (γ) and the correlation length (ν) are estimated. The obtained values of Tc are in good agreement with those obtained by magnetic measurements. The values of γ and ν are sensitive to the dilution ratio x. For the compounds situated in the ferromagnetic region (0.35 ≤ x ≤ 0.41), they are close to those of the 3D Heisenberg model. For the compounds presenting re-entrant behaviour (0.41 ≤ x ≤ 0.58), γ and ν deviate slowly from those of this model and approach the values found in re-entrant systems.