Magnetocaloric effect and inhomogeneity of CdCr2Se4 and HgCr2Se4 single crystals

Magnetocaloric effect in single crystals of spinels CdCr2Se4 and HgCr2Se4 is studied. The maximum value of the magnetic-field-induced change in entropy in the field of 15 kOe is about 1.4-1.5 J/(kg K). At Curie temperature the entropy change obeys the relation: −ΔS=αH^(2/3)-β. The magnetic transitions in the spinels are found to be noticeably smeared. The experimental data have been compared with the theoretical results obtained for Heisenberg model in the mean field approximation (MFA). It is found that MFA overestimates the change of entropy in a magnetic field and underestimates the influence of inhomogeneity on ΔS.