Structural And Magnetocaloric Properties Of Lu_1-xCa_xMnO₃

In the last two decades, the perovskite-like rare earth manganites have been wildlyinvestigated from fundamental researches and their potential applications in the magneticsensor, magnetic data storage and so on. As a kind of strongly correlated materials, theperovskite-like rare earth manganites exhibit many interesting and intriguing properties suchas complax magnetic phase transitions, colossal magnetoresistance (CMR), metal-insulatortransition, multiferroics. Large magentocaloric effect had been observed in perovskite-likematerials like La1-xAxMnO3, Nd1-xAxMnO3, Tb1-xAxMnO3etc (A=doped element).In this thesis, we focused on the structure and the magentocaloric properties of Ca dopedLuMnO3. A serie of polycrystalline samples Lu1-xCaxMnO3(0≤x≤0.6) had been prepared bythe traditional solid-state reaction method. The X-ray diffractions and Raman scatteringspectra had been investigated to identify the structural phase of the samples. The magneticproperties of the samples had been measured by a Physical Property Measurement System(PPMS, Quantum Design) and the magntic entropy SMhad been calculated at differenttemperatures T. The X-ray Photoelectron Spectroscopy had been used to get the photoelectronspectra of all the samples to clarify the Mn3+/Mn4+ratios of the samples with different Cadoping concentration. The main experimental results can be concluded as follows:1. The X-ray diffraction and Raman scattering spectra show that the sample is of ahexagonal phase with group P63cm at x=0. While0.1≤x≤0.4, the hexagonal phase withgroup P63cm and the orthorhombic phase with group Pbnm coexist in these samples. When x0.5, the samples are completely turned into a pure orthorhombic phase.2. The magnetic measurement show that the ferroic magnetization and the peak of-SM-T curve increase firstly and then decreases with the increasing of Ca dopingconcentration x, and reaches a maximum at x=0.4. A linear relationship between themaximum magnetic entropy change and the ferroic magnetization can be found.3. The X-ray photoelectron spectra show that the concentration of Mn3+decreaseslinearly with the increasing of Ca doping level x. At x=0.4, the Mn3+/Mn4+ratio gets close to 1. The maximums of the ferroic magnetization and the magnetic entropy at x=0.4could beattributed to the strong double exchange interaction between Mn3+and Mn4+.