Prediction of magnetocaloric effect using a phenomenological model in (x) La_0.6Ca_0.4MnO₃/(1 − x) La_0.6Sr_0.4MnO₃ composites

Abstract

This research paper presents a theoretical work on the magnetocaloric properties of (SC.4-2) composite obtained by mixing citric-gel La_0.6Ca_0.4MnO₃ (S0C1) and La_0.6Sr_0.4MnO₃ (S1C0), with mole fractions [0.875 (S0C1)/0.125 (S1C0)]. This mixture was then fritted at 900 °C. The magnetization of the composite goes in good agreement with the following relationship $M(\mathrm{S}\mathrm{C}.4{\text{-}}2)=0.865\times M(\mathrm{S}0\mathrm{C}1)+0.135 \times M(\mathrm{S}1\mathrm{C}0)$, where (0.865, 0.135) are the corresponding weight fractions to mole fractions (0.875, 0.125) of parent compounds [(S0C1) (S1C0)]. Resting upon this equality, the magnetic entropy change and the specific heat of composite were predicted at a constant field and pressure. The variation of the magnetic entropy $\left|{\Delta S}_{M}\right|$ and the heat capacity ${\Delta C}_{P,H}$ as a function of temperature of the two parent compounds (S0C1) and (S1C0), with a phenomenological model, were obtained in our previous research work. The values of the maximum magnetic entropy change ${\left|\left({\Delta S}_{M}\right)\right|}_{\mathrm{m}\mathrm{a}\mathrm{x}}$, full width at half-maximum ${\updelta} T_{\mathrm{F}\mathrm{W}\mathrm{H}\mathrm{M}}$ and relative cooling power (RCP), at several magnetic field variations, were determined. In addition to the S0C1 mother compound, the SC.4-2 composite displays the highest value of RCP, providing an estimate of the quantity of the heat transfer between the hot (T_hot) and cold (T_cold) ends during one refrigeration cycle. At a later stage, the study of the dependence on temperature of the magnetic entropy of (x) S0C1/(1 − x) S1C0 composites reveals that the optimum composition stands for x = 0.4. Indeed, it gives comparable contributions of two parent compounds, leading to a practically uniform variation of entropy over a wide temperature range.