Prediction of magnetocaloric effect using a phenomenological model in (x) La_(0.6)Ca_(0.4)MnO_3/(1-x) La_(0.6)Sr_(0.4)MnO_3 composites

摘要

This research paper presents a theoretical work on the magnetocaloric properties of (SC.4-2) composite obtained by mixing citric-gel La0.6Ca0.4MnO3 (S0C1) and La0.6Sr0.4MnO3 (S1C0), with mole fractions [0.875 (S0C1)/0.125 (S1C0)]. This mixture was then fritted at 900 degrees C. The magnetization of the composite goes in good agreement with the following relationship M(SC.4-2)=0.865xM(S0C1)+0.135xM(S1C0), 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 and the heat capacity Delta CP,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, full width at half-maximum delta TFWHM 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.