<p>Extensive <sup>75</sup>As nuclear magnetic resonance (NMR) studies were conducted on a variety of 122 iron-based superconductors. NMR frequency swept spectra and the spin-lattice relaxation rate (<i>T</i><sub>1</sub><sup>-1</sup>) were measured in CaFe<sub>2</sub>As<sub>2</sub> as a function of temperature. The temperature dependence of the internal hyperfine field was extracted from the spectra, and <i>T</i><sub>1</sub><sup>-1</sup> exhibits an anomalous peak attributed to the glassy freezing of domain walls associated with filamentary superconductivity. The field dependence of <i>T</i><sub>1</sub><sup>-1</sup> and subsequent bulk resistivity and magnetization measurements also show signatures of filamentary superconductivity nucleated at antiphase domain walls.
Systematic doping-dependent NMR studies were also carried out on Ni- and Co-doped BaFe<sub>2</sub>As<sub>2</sub>. In the Ni-doped variant, local magnetic inhomogeneities were observed via field swept NMR spectral analyses, and the doping dependence of the Néel temperature T<sub>N</sub> was confirmed by fits to (<i>T</i><sub>1</sub>T)<sup>-1</sup>(T). Spectral wipeout and stretched exponential relaxation behavior in the Co-doped variant reveal inhomogeneous behavior and the emergence of a cluster spin glass state. The NMR measurements bring into question the details of the phase transition from coexisting antiferromagnetism and superconductivity to pure superconductivity.
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:3602046 |
| Date | 04 January 2014 |
| Creators | Dioguardi, Adam Paul |
| Publisher | University of California, Davis |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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