Nuclear Magnetic Resonance Studies of the 122 Iron-Based Superconductors | Posted on:2014-02-15 | Degree:Ph.D | Type:Dissertation | University:University of California, Davis | Candidate:Dioguardi, Adam Paul | Full Text:PDF | GTID:1450390005486454 | Subject:Physics | Abstract/Summary: | | 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 Neel 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. | Keywords/Search Tags: | NMR, Magnetic, Studies, Superconductivity | | Related items |
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