A NMR-study on Nd₂CuO₄₋ₓFₓ and building a variable temperature and frequency NMR-probe
Abstract
A study of the Nd₂CuO₄₋ₓFₓ electron-doped high-TC superconductor
has been carried out, using ¹⁹F and ⁶³Cu NMR techniques as well as X-ray
diffraction. In order to do ¹⁹F NMR a spectrometer was set up and a homemade NMR-probe was used, allowing for variable temperature and frequency
studies. Both were extensively tested. Pseudo-single-crystals with identical
grain orientations were obtained at room temperature by an alignment procedure in a strong external field. The alignment quality was confirmed by X-ray
diffraction spectra which showed that the crystallites are aligning with the
c-axis perpendicular to the external field (unlike YBCO and its derivatives).
Extensive angle dependent ⁶³Cu NMR studies were done at room temperature.
The spectra obtained appeared to be unusual, and a hypothesis concerning the
uncommon alignment was formulated. However combining the alignment with
an electric field gradient failed to explain the NMR spectra. Next a model
was developed to explain them. When combining the alignment with a strong
shift anisotropy plus a small or even zero quadrupole interaction, a good agreement with the NMR spectra was found. Fluorine-NMR studies were done on
two out of four samples, finding resonances in both of them. Furthermore a
transferred magnetic field onto the fluorine sites was found and last but not
least a dependency of the applied field strength on the resonance MHz/T could
be established.
Type
Thesis, MPhil Master of Philosophy
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