Magnetocaloric effect near room temperature in (1-y)La sub(0.8)Ca sub(0.05)K sub(0.15)MnO sub(3)/yLa sub(0.8)K sub(0.2 )MnO sub(3) composites

Magnetic and magnetocaloric properties of (1-y) La sub(0.8)Ca sub(0.05)K sub(0.15)MnO sub(3)/yLa sub(0.8)K sub(0.2)MnO sub(3) with y=0.25, 0.5, and 0.75 composites were investigated. Our composites will be designated by CM sub(1) (y=0.25), CM sub(2) (y=0.5), and CM sub(3) (y=0.75). X-ray diffraction pattern show that La sub(0.8)Ca sub(0.05)K sub(0.15)MnO sub(3) and La sub(0.8)K sub(0.2)MnO sub(3) 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[Formulaomitted]c space group. The temperature dependence of the magnetization M(T) in the temperature range 200-350K shows that La sub(0.8)Ca sub(0.05)K sub(0.15)MnO sub(3) and La sub(0.8)K sub(0.2)MnO sub(3) samples exhibit a paramagnetic-ferromagnetic transition while decreasing temperature, with a Curie temperature T sub(C) increasing with K amount and reaching around 300K 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 [Formulaomitted] is found to be 5.32 and 4.37Jkg super(-1)K super(-1) under a magnetic field change of 5T for La sub(0.8)Ca sub(0.05)K sub(0.15)MnO sub(3) and La sub(0.8)K sub(0.2)MnO sub(3), respectively. Magnetic entropy change versus temperatures reveals that the composite CM sub(2) with y=0.5 exhibits the best value for the relative cooling power (RCP) of 270Jkg super(-1) under a magnetic field change of 5T. For y=0.25 and 0.75, the RCP is found to be around 227.5Jkg super(-1) under a magnetic field change of 5T for both of them. The RCP value of 270Jkg super(-1) for CM sub(2), which is around 66% of that observed in pure Gd makes our composite a potential candidate for magnetic refrigeration around room temperature.