The manganese (Mn) based perovskite oxide materials (manganites), of the chemical form T1-−xDxMnO3, display a large magnetic field induced decrease in their resistivity, termed colossal magnetoresistance. Typically, colossal magnetoresistance in the manganite samples is observed at low temperatures and high magnetic fields (>1 Tesla). However, an enhanced magnetoresistance at low magnetic fields and room temperature in these manganite samples would be technologically useful. In an effort to characterize this low magnetic field, room temperature magnetoresistance, the role of several different physical parameters has been explored in this thesis. These physical parameters include lattice mismatch strain, which originates from the epitaxial growth of single layer manganite thin films, the application of different radiation probes, such as microwave radiation, and the introduction of artificial grain boundaries in the form of interfaces in manganite multilayers.; Lattice mismatch strain originates from the difference in the lattice constants of the manganite thin film and the crystalline substrate. The nature of the effect of the lattice mismatch strain on these transport properties for La0.7Ba0.3MnO3 thin films has been studied by varying the degree of lattice mismatch strain in the thin film. Variation of the lattice mismatch strain was achieved by varying the thickness of the manganite thin films, by annealing the manganite thin films in oxygen, and by buffering the manganite films with a lattice matched buffer layer. Each of these approaches relaxed the lattice mismatch strain, resulting in an increase of the low magnetic field, room temperature magnetoresistance.; Microwave radiation probes determine the magnetic homogeneity of the manganite thin films and the effect of this magnetic homogeneity on the low magnetic field, room temperature magnetoresistance. La0.7Ba 0.3MnO3 thin films showed no gross magnetic homogeneitiese. The magnetic homogeneity increased in the La0.7Ba0.3MnO 3 thin films when the lattice mismatch strain in the film decreased. In addition, as the crystalline quality and the magnetic homogeneity of the thin films increased, the microwave magnetoresistance also increased.; The decrease of the lattice mismatch strain in the manganite thin films ultimately led to an increase in the low magnetic field, room temperature magnetoresistance. However, this enhancement was minimal, so artificial grain boundaries in the form of interfaces in manganite spin valves and spin dependent tunneling junctions were introduced. However, no room temperature, low magnetic field magnetoresistance was observed in either device, due to the decrease of the manganite spin polarization with increasing temperature, the occurrence of spin flip scattering events at defect sites in the multilayer structure, and reorganization of the magnetization at the interfaces. (Abstract shortened by UMI.)
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机译：化学形式为T 1--x D x MnO 3 的锰（Mn）基钙钛矿氧化物材料（锰）大磁场导致其电阻率降低，称为巨磁电阻。通常，在低温和高磁场（> 1特斯拉）下观察到锰矿样品中的巨大磁阻。然而，这些锰矿样品在低磁场和室温下增强的磁阻在技术上是有用的。为了描述这种低磁场，室温磁阻的特性，本文研究了几种不同物理参数的作用。这些物理参数包括晶格失配应变，其源于单层锰矿薄膜的外延生长，不同辐射探针（如微波辐射）的应用以及在锰矿多层中以界面形式引入人工晶界。晶格失配应变起因于锰矿薄膜和结晶基质的晶格常数的差异。通过改变La 0.7 Ba 0.3 MnO 3 薄膜，研究了晶格失配应变对这些传输性质的影响的性质。薄膜中晶格失配应变的程度。通过改变锰矿薄膜的厚度，通过在氧气中对锰矿薄膜进行退火以及通过用晶格匹配的缓冲层来缓冲锰矿膜，可以实现晶格失配应变的变化。这些方法中的每一种都缓解了晶格失配应变，导致低磁场，室温磁阻的增加。微波辐射探针确定锰矿薄膜的磁性均匀性，以及这种磁性均匀性对低磁场，室温磁阻的影响。 La 0.7 Ba 0.3 MnO 3 薄膜无明显的磁性均匀性。薄膜的晶格失配应变减小时，La 0.7 Ba 0.3 MnO 3 薄膜的磁均匀性增加。另外，随着薄膜的结晶质量和磁均匀性的增加，微波磁阻也增加。锰薄膜中晶格失配应变的减少最终导致低磁场，室温磁阻的增加。但是，这种增强作用是最小的，因此引入了锰自旋阀和自旋相关的隧道结中的界面形式的人造晶界。然而，由于锰锰矿自旋极化随温度升高而降低，在多层结构的缺陷部位发生自旋翻转散射事件以及在多层结构中的磁化重组，因此在任一器件中均未观察到室温，低磁场磁阻。接口。 （摘要由UMI缩短。）
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