Investigation of structural, magnetic and magnetocaloric properties of (La1-xREx)0.85K0.15MnO3 (RE = Pr ve Sm) manganite compounds

In this study, (La1-xREx)0.85K0.15MnO3 (RE = Pr ve Sm) manganite compounds prepared by sol-gel method have been investigated the structural, magnetic and magnetocaloric properties. In order to analyse crystal structures and surface morphology of samples, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) measurements were carried out. From the XRD analyses, while the crystal structure is found as rhombohedral for 0.0 ≤ x ≤ 0.2 in (La1-xPrx)0.85K0.15MnO3 compounds. It is found as orthorhombic for x = 0.3, 0.5 and 1.0. In the (La1-xSmx)0.85K0.15MnO3 series, the crystal structure is found as rhombohedral for all concentration of Sm. It is observed from the SEM images that the samples consist of highly aggregated grains in different polygonal forms. All elements composed of compounds have been observed in EDS spectra. The magnetic properties of the samples were investigated by temperature-dependent, M(T), and magnetic-field-dependent, M(H), magnetizations measurements. From the M(T) curves it is observed that samples have ferromagnetic-paramagnetic phase transition, and the magnetic phase transition temperature of the samples decrease with the substitution of Pr and Sm for La. The magnetic entropy change and relative cooling power (RCP) values of the samples have been indirectly calculated around magnetic phase transition temperature. In the thesis work, the largest maximum magnetic entropy change value was calculated as 7. 96 Jkg-1K-1 under 5 T for x= 0.1 in (La1-xPrx)0.85K0.15MnO3 series.