Nuclear quadrupole resonance

About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.

Frequency detection system comprising circuitry for adjusting the resonance frequency of a high temperature superconductor self-resonant coil

Abstract: The use of a circuit to adjust the resonance frequency of a high temperature superconductor self-resonant transmit, receive, or transmit and receive coil results in improved performance. The circuit is useful in a frequency detection system, especially in a nuclear quadrupole resonance detection system.

Fourier transform pure nuclear quadrupole resonance by pulsed field cycling

Abstract: We report the observation of Fourier transform pure NQR by pulsed field cycling. For deuterium, well resolved spectra are obtained with high sensitivity showing the low frequency nu0 lines and allowing assignments of quadrupole couplings and asymmetry parameters to inequivalent deuterons. The technique is ideally applicable to nuclei with low quadrupolar frequencies (e.g., 2D, 7Li, 11B, 27Al, 23Na, 14N) and makes possible high resolution structure determination in polycrystalline or disordered materials.

17O NMR–NQR study of molecular motion in the liquid, and α and β solid phases of CO

Abstract: A comprehensive NMR−NQR study of carbon monoxide enriched 24.5% in 17O (I = 5/2) is reported, which provides interesting information on the motions of the CO dipoles in the liquid and in the a and b solid phases. In the liquid phase the 17O NMR spin‐lattice relaxation due to the tumbling rotational motions of the molecular axis, combined with the experimental evaluation of the rigid electric field gradient (EFG) at the 17O site has been utilized to achieve a direct and precise measurement of the reorientational correlation time of the dipole and its temperature dependence. In the b phase, the quadrupole perturbed NMR spectra and the spin‐lattice relaxation indicate the occurrence of a precessional motion of the dipole around the c axis. An effective EFG is consequently present, whose order of magnitude is about 103 smaller than the static one. The precessional correlation time is derived, which is surprisingly very close to the reorientational correlation time of the liquid phase, suggesting a quasifree rotation character for the precession. 17O NQR signals in the a phase have been detected and resonance frequencies and linewidths have been measured. From the temperature behavior of the NQR frequency, information on the local order parameter for the librational motion of the dipoles is obtained. The linewidth exhibits a peculiar temperature dependence, with a maximum around 37 K and a dramatic divergence for T→29 K. While an orientational static disorder could be expected in view of the residual entropy, it is shown how the linewidth, as well as some pure quadrupole relaxation measurements, seem to indicate the occurrence in the a phase of a dynamical disorder, with sudden head‐to‐tail reorientations of the dipole, at least for T≳29 K. In the framework of such a dynamical model, a theoretical picture for the motional contribution to the NQR allows one to obtain insights on the features of the orientational disordering processes. The hypothesis of a phase transition of antiferroelectric type below T?37 cannot be ruled out. Finally, some evidence of softening of the libronic frequencies on approaching the a–b phase transition is obtained.

Ferromagnetic and Triplet-Pairing Instabilities Controlled by Trigonal Distortion of CoO6 Octahedra in NaxCoO2·yH2O

Abstract: In the recently discovered Co-oxide superconductor Na x CoO 2 · y H 2 O, the edge-shared CoO 6 octahedra are trigonally contracted along the c -axis in the CoO 2 -plane. We study how this CoO 6 distortion affects the magnetic properties and superconductivity in this compound by analyzing the multiorbital Hubbard model using the fluctuation-exchange approximation. It is shown that through generating the trigonal crystal field, the distortion pushes the Co e ′ g bands up and consequently gives rise to the hole-pocket Fermi surfaces, which have been predicted in the band calculations. As the distortion increases, the hole pockets are enlarged and the ferromagnetic fluctuation as well as the pairing instability increases, which is in good agreement with recent NQR results.