Different entropy calculation methods in magnetocaloric materials

In this study, magnetocaloric effect measurement and calculation methods used in the literature are examined. In magnetocaloric effect measurements and calculation methods, La0.67Ca0.33-xMgxMnO3 (x = 0, 0.02, 0.05, 0.1, 0.2, 0.33) compounds produced by solid state reaction method were taken as examples. Firstly, the structural and magnetic properties of the produced compounds were investigated. X-ray analyses indicated that the substitution of Ca by Mg produced no considerable structural change and only the diffraction peaks for orthorhombic symmetry were obtained for all samples. The decrease in saturation magnetisation and Curie temperature (267 K for x=0 and 96 K for x=0.33) were attributed to weakening of the ferromagnetism in Mg doped samples. Maximum magnetic entropy change was calculated in two different ways by using Maxwell equations and Landau theory. The maximum value of the magnetic entropy change at 1 T decreased from 4.07 J/kg K for x = 0 to 0.41 J/kg K for x = 0.33. The results calculated by both methods were found to be in agreement with each other.