Extensive 75As 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 (T 1-1) were measured in CaFe2As2 as a function of temperature. The temperature dependence of the internal hyperfine field was extracted from the spectra, and T1 -1 exhibits an anomalous peak attributed to the glassy freezing of domain walls associated with filamentary superconductivity. The field dependence of T1-1 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 BaFe2As2. In the Ni-doped variant, local magnetic inhomogeneities were observed via field swept NMR spectral analyses, and the doping dependence of the Néel temperature TN was confirmed by fits to (T 1T)-1(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.
|Advisor:||Curro, Nicholas J.|
|Commitee:||Curro, Nicholas J., Scalettar, Richard T., Zieve, Rena|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 75/03(E), Dissertation Abstracts International|
|Subjects:||Physics, Condensed matter physics|
|Keywords:||Antiferromagnetism, Bafe2as2, Cafe2as2, Iron-based superconductors, Nmr, Superconductivity|
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