| Manganese oxide La1-xCaxMnO3with perovskite structure are paid great attention due to the discovery of colossal magnetoresistive effect inside. The complex interactions among the charge, orbital, spin and lattice give rise to the abundant physics properties, such as metal-insulator transition, magnetic transition, charge-ordering and phase separation. Manganese oxides like La1-yRyRexMnO3(R: rare earth elements Y, Prand Nd ect. with trivalence; Re:alkali elements Ca, Srand Ba ect. with double valence) are deduced from a matrix compound LaMnO3by doping on La sites, resulting in Mn ions with different valences, and consequently changing the crystal structure, electronic and magnetic properties of the matrix, and even intrinsic inhomogeneity at microscale. The inhomogeneity at microscale will inevitably induce the inhomogeneity of dielectric constant and magnetic susceptibility, which can be sensed by its far-infrared spectra. The spectra are sensitive to the vibration modes that are closely related to the electron-photo interaction, electron transition between interbands or intrabands and magnetic transitions.The Y-doped manganese oxides La2/3-xYxCa1/3Mn03(x=0,0.07,0.1, and0.14) were sintered by a solid-state method. Their crystal structures, magnetic and electronic transport properties, reflectivity of mid/far infrared radiation spectra, and laser confocal microscopic Raman spectra were checked and characterized. The whole thesis is arranged as follow.In chapter one, a brief introduction on the crystal structures, electro-magnetic properties, characterization methods of manganites and the aim of the thesis was expressed.In chapter two, much attention was paid to the preparation of La2/3-xYxCai/3Mno3(X=0,0.07,0.1, and0.14) and the experimental setup of infrared and laser confocal microscopic Raman spectra analysis.In chapter three, a X-ray diffractionmeter was employed to analyze structure of=0,0.07,0.1, and0.14). The resistivity of the samples were detected by a four-probe method from75K-300K; for lower doping-level samples, is was found a metallic state at low temperature and insulator-like conducting state at high temperature. And the transition temperature moves towards lower temperature with Y doping and the transition even disappears at x=0.14, in which the sample only shows an insulating behavior. The diffraction peaks move to the high angle for the four samples with Y increasing. The magnetic properties of these manganese La2/3-xYxCa1/3MnO3(x=0,0.07,0.1, and0.14) were checked with a SQUID under H=10Oe. It was found that ferromagnetic transition temperature (i.e. the Curie temperature Tc) decrease significantly with incensement of Y doping. When the doping level x=0.14, the sample does not show the paramagnetic to ferromagnetic transition, replaced by a paramagnetic to antiferromagnetic transition instead.In chapter five, the infrared optical properties and Raman spectra of the samples were shown. For the undoped sample, four characteristic peaks in the far infrared radiation spectrum can be found at high temperatures and with the decrease of temperature two of them gradually fade away. The peak positions show a great change around the magnetic transition temperature of the sample. For the Y-doped samples, the four peaks become clearer. Although their magnetic properties also show sharp changes, the shape of the four peaks is stable and almost independent of temperature. However, there is a manifest change in the mid infrared radiation spectrum around the magnetic transitions. A qualitative explanation was proposed for the above results by taking the lattice vibration modes of Jahn-Teller effect in the Mn-o octahedral lattice into consideration. Three obvious characteristic peaks, high wave number peaks (～610cm-1), medium wave number peaks (～450cm-1) and low wave number peaks (～220cm-1), appear in Raman spectrum for each sample.But the other three peaks show no obvious changes with temperature. |
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