Characterization of structural, magnetic, and magnetocaloric properties of LaCaPbMn1-xAxO3 (A: Ni, Bi) manganites

In this thesis study, La-based manganite materials exhibiting low magnetic hysteresis have been investigated due to their ease and relatively low cost of production, chemical stability, and second-order magnetic transition. The solid-state reaction method was used in the production of the materials. Within the scope of the study, the effects of the substitution of Ni and Bi elements for Mn in certain proportions in the Mn region of the La0.65Ca0.20Pb0.15Mn1-xAxO3 ana phase on the structural, magnetic, and magnetocaloric properties of the materials have been investigated. The crystal structures of the produced materials were determined by X-ray Diffractometry (XRD), the surface morphology by Scanning Electron Microscopy (SEM), and the elemental analysis by Energy Dispersive X-ray Spectroscopy (EDS). It was determined that all produced materials have a rhombohedral crystal structure in the R3 ̅c space group. When the surface morphologies were examined, it was observed that all materials had a dense packing structure and polygonal formations. The magnetic properties of the materials were investigated using a Physical Properties Measurement System (PPMS). The magnetic properties of the materials were determined by temperature-dependent M(T) and field-dependent M(H) measurements. From the magnetic measurement results, it has been observed that the change of the Mn region with Ni and Bi brings the transition temperatures of the materials closer to room temperature. It was observed that there was an improvement in the magnetocaloric properties of the Bi-doped samples. Keywords: Magnetocaloric Effect, Magnetic Refrigeration Systems, Curie Temperature, Entropy Change