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.