Synthesis and characterization of novel electronic and magnetic systems

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Date
2016
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University of Alabama Libraries
Abstract

Fabrication and characterization of novel electronic and magnetic materials are pursued under two main subjects during this dissertation: Part I deals with the low frequency noise spectroscopy of vanadium dioxide (VO2) thin films in the vicinity of the first-order metal-insulator transition (MIT). High quality epitaxial thin films of vanadium dioxide were deposited on TiO2 substrates using chemical vapor deposition methods and characterized for our investigations. The design and characterization of our home-built “cross-spectrum” analyzer, which was used for the fluctuation spectroscopy of VO2 films, is explained. 1/f noise analysis of vanadium dioxide across the MIT shows the significant increase of noise amplitude, which can be explained by “Local interference” model. Energy distribution investigations in this material showed the signature of the percolation model. Critical exponent studies are suggestive of the p-noise model as the mechanisms governing the electronic processes in VO2. Evidence of anisotropic electrical transport along different crystallographic axes of VO2 is presented by the conductance, Hall measurements and noise spectroscopy of the patterned VO2 films. Part II of this dissertation presents the systematic, theoretical, experimental and analytical search for novel half-metallic Heusler compounds. Experimental and analytical methods to synthesize and characterize these new materials in polycrystalline bulk form are thoroughly discussed. As a result of our investigation a new Heusler material with the composition of Fe1.5TiSb was synthesized and was recognized as the most stable compound in FexTiSb systems. The theoretical investigations of this system are suggestive of an alternative L21/C1b layered structure for this new phase of material with weak magnetism and metallic characteristics. Our investigations for finding half-metallic Heusler Fe2MnGe led to synthesizing this compound with the hexagonal DO19 structure. This material has a high magnetic moment and uniaxial crystalline anisotropy, which is a step toward finding the half-metallic hexagonal Heusler compounds with applications in perpendicular media and CPP-GMR.

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Electronic Thesis or Dissertation
Keywords
Condensed matter physics, Materials science
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