▎ 摘　　要

La0.7Ca0.3MnO3 perovskite and its composites with graphene nanoplatelet (GNP) were prepared using a wet chemical method. The structural, magnetic and magnetocaloric properties of La0.7Ca0.3MnO3: GNP composites were investigated to determine the effect of GNPs. The results of XRD analysis show that the synthesised powders can be almost indexed to pure phase orthorhombic La0.7Ca0.3MnO3. The magnetic measurements demonstrate that 0.7 and 1% GNP amounts cause an increase in the Curie temperature (T-C), and for larger amounts of GNP, the T-C monotonically decreases, except for the sample with 10% GNP. The results obtained from the Arrott plots show that the magnetic phase transition of the samples transforms from the first to second order with increasing GNP amount. The changes in the magnetocaloric properties are interpreted in terms of perovskite phase formations via structural analysis. The amounts of graphene nanoplatelets in the oxide powders are correlated with the observed magnetocaloric properties. The best magnetocaloric performance with the maximum magnetic entropy change of 3.99 Jkg(-1)K(-1) and refrigeration capacity of 90 Jkg(-1) was obtained at a 2 T magnetic field.