Disorder and Doping in the Oxygenated Electron-doped Superconductor PCCO
Disorder and Doping in the Oxygenated Electron-doped Superconductor PCCO
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Date
2006-08-29
Authors
Higgins, Joshua Scott
Advisor
Greene, Richard L
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Abstract
This thesis is composed of two parts: the first part deals with the
high temperature electron-doped superconductor
Pr_(2-x)Ce_(x)CuO_(4-delta); the second part deals with the
diluted magnetic semiconductor Ti_(1-x)Co_(x)O_(2-delta).
It is not clear why oxygen reduction and cerium doping are necessary
to obtain superconductivity in the electron-doped
Pr_(2-x)Ce_(x)CuO_(4-delta). I investigated the effects of
oxygenation in this material using resistivity and Hall
measurements. For various oxygen contents, I was able to determine
that there is a separable doping and a disorder contribution to the
superconducting transition temperature. I was able to quantitatively
separate out these two effects and show that these two effects are
opposite with regards to changes in T_(c) for overdoped thin
films. The disorder component is roughly twice as large as the
doping component. This analysis is also shown to be self consistent
in demonstrating that the doping component of oxygen variation
follows the trends of Cerium doping.
For the diluted magnetic semiconductor
Ti_(1-x)Co_(x)O_(2-delta), I investigated the intrinsic
nature of the ferromagnetism observed in thin films. Hall effect
measurements were used as the technique because ferromagnetic
materials exhibit an anomalous Hall effect, which is due to an
interaction between the charge carriers and the magnetic moments. I
found that low carrier concentration anatase phase films did not
exhibit an anomalous Hall effect, whereas high carrier concentration
rutile phase films do. The presence of the anomalous Hall effect at
this point cannot be attributed to an intrinsic ferromagnetism as
cobalt clusters are observed in these films.