Magnetocaloric effect near room temperature in (1 - y)La0.8Ca0.05K0.15MnO3/yLa0.8K0.2MnO3 composites

Magnetic and magnetocaloric properties of (1 - y) La0.8Ca0.05K0.15MnO3/yLa0.8K0.2MnO3 with y = 0.25, 0.5, and 0.75 composites were investigated. Our composites will be designated by CM1 (y = 0.25), CM2 (y = 0.5), and CM3 (y = 0.75). X-ray diffraction pattern show that La0.8Ca0.05K0.15MnO3 and La0.8K0.2MnO3 samples, elaborated using the solid state reaction at high temperature, are single phase without any detectable impurity and crystallize in the rhombohedral system with R anti 3c space group. The temperature dependence of the magnetization M(T) in the temperature range 200-350 K shows that La0.8Ca0.05K0.15MnO3 and La0.8K0.2MnO3 samples exhibit a paramagnetic-ferromagnetic transition while decreasing temperature, with a Curie temperature TC increasing with K amount and reaching around 300 K for x = 0.2. The field dependence of the magnetization M(H) confirms the ferromagnetic behavior at low temperatures observed in the M(T) curves. The maximum of the magnetic entropy change vertical stroke ΔSMmax vertical stroke is found to be 5.32 and 4.37 J kg-1 K-1 under a magnetic field change of 5 T for La0.8Ca0.05K0.15MnO3 and La0.8K0.2MnO3, respectively. Magnetic entropy change versus temperatures reveals that the composite CM2 with y = 0.5 exhibits the best value for the relative cooling power (RCP) of 270 J kg-1 under a magnetic field change of 5 T. For y = 0.25 and 0.75, the RCP is found to be around 227.5 J kg-1 under a magnetic field change of 5 T for both of them. The RCP value of 270 J kg-1 for CM2, which is around 66% of that observed in pure Gd makes our composite a potential candidate for magnetic refrigeration around room temperature. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)