Scaling Laws for the Magnetocaloric Effect in Calcium Deficiency Manganites La0.8Ca0.2−x□xMnO3 with a Second-Order Magnetic Phase Transition

The magnetic entropy change (Δ S M ) of polycrystalline samples La 0.8 Ca 0.2− x □ x MnO 3 ( x =0.00; x =0.10 and x =0.20) with a second-order phase transition has been investigated. The field dependence of the magnetic entropy change expressed as Δ S M ∝ H n follows the phenomenological curves and at the temperature of the peak corresponds to a large field independent exponent of n =0.581; 0.642 and 0.671 for x =0.00; x =0.10 and x =0.20 samples, respectively. Then, we have constructed the phenomenological universal curve by normalizing the magnetic entropy change curves with respect to their maximum values, , and rescaling the temperature axis. These universal curves collapse onto a single curve for any applied magnetic field for all samples. Moreover, we note that the universal curve for x =0.10 and x =0.20 samples collapses with a small deviation compared with x =0.00 sample. This is consistent with our previous work where we demonstrated that the magnetic phase transition relative to the samples x =0.00 belongs to the 3D-Ising universal class and to the 3D-Heisinberg class for x =0.10 and x =0.20 samples. This universal curve can be used to predict the response of materials in different conditions not available in the laboratory by extrapolations in field or temperature.