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 Title: Irreversibility line, Hall effect, and longitudinal resistivity measurements on cobalt-doped yttrium barium(2) copper(3) oxygen(7-delta) Author(s): Neiman, Regina Lynn Doctoral Committee Chair(s): Ginsberg, Donald M. Department / Program: Physics Discipline: Physics Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Physics, Condensed Matter Abstract: We have developed a procedure for growing high-quality single crystals of YBa$\sb2$(Cu$\sb{\rm 1-x}$Co$\sb{\rm x})\sb3$O$\sb{7-\delta}.$ By high-pressure oxygen annealing, we produced single crystals having transition temperatures, T$\sb{\rm c}$, comparable with those of polycrystalline samples of the same cobalt concentration.We have investigated the effect of cobalt on T$\sb{\rm c}$ and the DC irreversibility line. As seen previously, we found that the dependence of T$\sb{\rm c}$ on the concentration of cobalt changes at the orthorhombic-to-tetragonal phase transition. We also found that the DC irreversibility line changes functional form at approximately 2.5% to 3% cobalt substitution, where the orthorhombic-to-tetragonal phase transition occurs.We have measured the in-plane Hall effect and the in-plane resistivity of cobalt-doped YBa$\sb2$Cu$\sb3$O$\sb{7-\delta}$ single-crystal samples. The sign-reversal in the Hall effect below T$\sb{\rm c}$ disappears at approximately the orthorhombic-to-tetragonal phase transition. The resistivities were converted into conductivities to investigate the field dependence of the Hall effect. The Hall conductivity, $\sigma\sb{\rm xy},$ is the sum of two terms, C$\sb1$/H and C$\sb2$H, where C$\sb1$ and C$\sb2$ are field-independent but temperature-dependent. The temperature dependences of C$\sb1$ and C$\sb2$ were qualitatively unaffected by cobalt-doping.From our measurements, it appears that the orthorhombic-to-tetragonal phase transition is important in the behavior of cobalt-doped Y?BCO samples. In order to explain the effect of cobalt on YBCO, it seems that more emphasis should be put on understanding what happens when the sample changes phase from orthorhombic to tetragonal. Issue Date: 1995 Type: Text Language: English URI: http://hdl.handle.net/2142/21413 Rights Information: Copyright 1995 Neiman, Regina Lynn Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9543683 OCLC Identifier: (UMI)AAI9543683
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