![]() Theoretical expressions are derived for the equilibrium nuclear magnetization in a static magnetic field of a collection of nuclear spins imbedded in s crystalline lattice. « lessĪn investigation has been made of the direct electrical induction of nuclear-quadrupole-spin transitions in a gallium-arsenide single crystal. At either of two fourth rank magic angles, a simple three parameter lineshape is obtained, and the three breakpoints are related directly to the quadrupolar constant and its asymmetry parameter. A straightforward approach is presented that combines average Hamiltonian theory and a numerical solution of a classical banded matrix describing the equation of motion for a quadrupolar nucleus under variable angle sample spinning conditions. Broadening of the central transition of quadrupolar nuclei with half integer spins is caused by the anisotropy of the second order quadrupolar interaction. NMR spectroscopy of quadrupolar nuclei in solids generally yields broad lines even when magic angle spinning is applied. Consideration of the dipolar-CSA cross-correlated spectral densities not only improves the accuracy of the measurement of dipolar spectral densities but also allows for the determination of the dipolar-CSA cross-correlated spectral densities themselves, providing a new measure of the anisotropy of the shielding tensor. Dipolar-CSA cross-correlated spectral densities introduce relaxation pathways more » that couple together magnetization modes with different spin inversion symmetries. The cross-correlation between the dipolar and chemical shift anisotropy (CSA) interactions is found to be appreciable. In addition, the CH coupled spin relaxation can characterize the methyl internal rotation dynamics. Simultaneous fitting of the resulting relaxation curves with various rates and initial conditions allows for the extraction of both auto- and cross-correlated dipolar spectral densities which can provide detailed information on the molecular anisotropic reorientation. The carbon-13 multiplet spin-lattice relaxation in CH and CH spin systems is studied in detail by various nonselective and selective pulse techniques. The feasibility of NQR-NMR studies in small metal particles in the presence of strong inhomogeneous quadrupole interactions is assessed « less ![]() Measurements of relaxation rates yield T/sub 1/T = 0.03 sK, indicating a relaxation mechanism driven by the hyperfine interaction with the conduction electrons. The spectra obtained in the presence of an external magnetic field can be interpreted satisfactorily in terms more » of transitions among the eigenstates of the full Hamiltonian (Zeeman plus quadrupolar). The average quadrupole coupling frequencies measured at 5 K are, for the two isotopes. The zero-field NQR spectrum is severely broadened by a nonuniform distribution of quadrupole interactions. The nuclear-magnetic-resonance and nuclear-quadrupole-resonance (NQR-NMR) spectra of /sup 187/Re and /sup 185/Re in a powder of rhenium metal were measured in the temperature range 5-10 K both in zero field and with an external magnetic field.
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