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The Boundary Magnetoresistance Effect of La2/3Ca1/3MnO3 Doped SiO2

Author: LiuDeWei
Tutor: XiaZhengCaiï¼›YuanSongLiu
School: Huazhong University of Science and Technology
Course: Materials Physics and Chemistry
Keywords: Manganese-based perovskite oxide Ferromagnetic metal particles Heterostructure Grain boundary Magnetoresistance
CLC: TB332
Type: Master's thesis
Year: 2005
Downloads: 50
Quote: 0
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Abstract


Manganese-based perovskite oxides due to the existence of complex electronic, lattice, spin and other interactions, and these interactions can be changed according to need artificial Therefore, such compounds for people to study strongly correlated electron system provides a an ideal natural laboratory in condensed matter physics, materials physics and other areas of the main object of study. Especially in recent years found in the class oxides have potential applications in large magnetoresistance (CMR) after more inspired people to its research enthusiasm. However, since these magnetoresistance effect mainly in the low temperature range (far below the Curie temperature), and its size decreases rapidly with increasing temperature, thus limiting the effect of this magnetic resistance device in the actual application. In this thesis, to merit doped perovskite manganese-based oxide La 2 / 3Ca 1 / 3MnO 3 as the substrate, with its Z oxides SiO 2 for compounding, through its heterogeneity modified grain boundaries, thereby to change the manganese-based perovskite oxides La 2 / 3Ca < sub> 1 / 3MnO 3 ferromagnetic coupling strength between the particles, and ferromagnetic particles between the electric and magnetic transport behavior were studied. For the development of near room temperature, the lower the applied magnetic field having a magnetic resistance effect was magnetoresistance materials provide experimental and theoretical basis. Studies are as follows: The first chapter of the manganese-based oxide perovskite structure and magnetic properties of electrical transport behavior of a more comprehensive overview, based on this theory anthology presents topics and significance; Chapter detailed description of the sample preparation process, including the solid state reaction method, sol - gel method and the specific preparation process a variety of materials, and the samples prepared by different processes were analyzed, trying to find the best samples we need preparation process; chapter outlines the single-phase polycrystalline materials La 2 / 3Ca 1 / 3MnO 3 basic characteristics on the basis of studied the heterogeneous phase SiO 2 content on the La 2 / 3Ca 1 / 3MnO 3 electrical transport behavior and magnetic properties. Experimental results show that: compared with pure La 2 / 3Ca 1 / 3MnO 3 compared to the entire composite sample of the metal - insulator transition temperature TP significantly The move to higher temperature, while its resistance value decreases; when SiO 2 content x lt; 0.02, with the SiO 2 content increases, the increase in the system TP, resistance value decreases; when SiO 2 concentration x gt; 0.02, with the SiO 2 content increases, the system TP relatively lower, the resistance value has increased ; More importantly, all the samples at room temperature, the composite showed the grain boundaries near the magneto-resistance effect, and this magnetic resistance effect occurs over a wide temperature range. In addition, by scanning electron microscopy and X-ray spectral analysis of the heterogeneous phase SiO 2 in the matrix phase La 2 / 3Ca 1 / 3MnO 3 in the distribution; Chapter IV La 2 / 3Ca 1 / 3Mn 1-x Si x O 3 doped system microstructure and electrical transport properties have been studied, the experimental results show that the Si 4 ionic radius (0.40 A) than Mn 4 ionic radius (0.54 A) small, La 2 / 3Ca 1 / 3MnO 3

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