Magnetic, magnetocaloric, magnetotransport and magnetoresistance properties of calcium deficient manganites La0.8Ca0.2−x□xMnO3 post-annealed at 800°C

[Display omitted] •Structural transition from orthorhombic to rhombohedral structure in La0.8Ca0.2−x□xMnO3 compounds.•Enhancement of TC for the rhombohedral samples.•A large magnetocaloric effect which give the possibility of application in the magnetic refrigeration area.•High values of the magnetoresistance in all samples. La0.8Ca0.2−x□xMnO3 compounds were prepared by the solid-state reaction with 0.00⩽x⩽0.20, annealed at high temperature and post annealed at 800°C. Structural, magnetic and electrical measurements were performed to examine the effect of the calcium deficiency on the physical properties. The XRD data have been analyzed by Rietveld refinement technique. We have noticed that the calcium deficiency causes a structural transition form an orthorhombic structure with Pnma space group to a rhombohedral one with R3‾c space group, and an increase of the unit cell volume. Magnetization versus temperature study has shown that all samples exhibit a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase when increasing temperature. All samples present a large magnetocaloric effect which reaches 8J/Kkg under magnetic field of 5T for x=0.00. Moreover, the temperature dependence of electrical resistivity shows a metal–insulator transition at Tρ for all samples. The electrical resistivity is fitted with the phenomenological percolation model. Hence, we found that the estimated values of the resistivity are in good agreement with experimental data. Above all, the magnetoresistance study showed a peak which has a great value around the insulator–metal transition temperature.