Presence Of Quadrupolar Interactions Research Articles

Progressive saturation NMR relaxation

The NMR spin-lattice relaxation rate, ${T}_{1}^{\ensuremath{-}1},$ can be measured precisely by progressive saturation. This efficient technique is useful when ${T}_{1}$ is long and the NMR signal is weak. We derive the quasiequilibrium spin response to excitation in the case of a Zeeman spectrum in the presence of quadrupolar interactions. Exact solutions for the recovery of magnetization under the influence of purely magnetic fluctuations for $I=\frac{1}{2},$ $\frac{3}{2},$ and $\frac{5}{2}$ are presented. This is the general solution to a problem that has been previously solved only for the $I=\frac{1}{2}$ case. An important example for the application of this technique is ${}^{17}\mathrm{O}$ NMR in cuprate superconductors $(I=\frac{5}{2}).$ We show comparisons of the theory with the relaxation measured for high-temperature superconducting materials and the NMR-rates measured by this technique across the vortex-broadened spectrum at low temperature.

Deuterium polarization transfer in rotating solids and its application in structural investigation

The transfer of deuterium spin order in rotating solids has been studied theoretically and experimentally. In the presence of quadrupolar interactions, 2H polarization transfer is enhanced by magic-angle sample spinning (MAS) through a mechanism analogous to the rotational resonance effect in a pair of coupled homonuclear spins-1/2. The master equation that describes the exchange of spin order between two 2H spins interacting with extraneous spins is presented, and its predictions are compared with experimental results. The comparison shows that polarization transfer under MAS can be used to measure the distance between two 2H spins if their dipolar coupling is large compared with the homogeneous linewidth. It is also demonstrated that the relative orientation between 2H quadrupolar coupling tensors can be obtained from a 2D polarization-transfer experiment under MAS.

Spatially resolved homonuclear solid-state NMR. II. Jeener-Broekaert and solid-echo phase-encoding imaging

Phase encoding is a principle which is employed in several solid-state NMR imaging techniques. It is applicable to all kinds of spin echoes occurring in solid-state NMR. The exemplary density-operator theories for solid-echo as well as for Jeener-Broekaert phase-encoding imaging (JEPHI) are outlined, providing physical insight into the phase-encoding process with this type of experiment. At the same time, the basis for the theory of further solid-echo pulse sequences in the presence of magnetic field gradients is laid. The treatment is based on dipolar interaction although it is argued that the same pulse sequences work also in the presence of quadrupolar interaction. With ideally hard radiofrequency pulses the considered phase-encoding techniques permit the straightforward evaluation of image data. Artifacts appearing in images are suitably classified and physically explained. With softer RF pulses the tendency toward image artifacts increases. This can be alleviated by phase-cycling procedures. Corresponding pulse sequences and experiments are reported. A particularly favorable feature of this class of solid-state imaging techniques is that the pulse sequences can easily be implemented on standard tomographs.

Magnetic properties of PrX2 compounds (X = Pt, Rh, Ru, Ir) studied by hyperfine specific heat, magnetization and neutron-diffraction measurements

Abstract Magnetic ordering phenomena in rare-earth intermetallic compounds can be unravelled most advantageously in the case of simple crystallographic structure and when a combination of microscopic techniques is applied. Here we shall present the temperature and magnetic field dependence of the magnetic moment of the cubic PrX2 compounds (X = Pt, Rh, Ru, Ir), as inferred from hyperfine specific-heat, magnetization and neutron-diffraction measurements. The results are compared with a mean-field calculation, taking crystalline electric field and bilinear (dipolar) exchange interactions into account. Adopting experimental values of the Lea, Leask and Wolf parameters x and W from inelastic neutron scattering results, we find satisfactory agreement between our magnetic data and the mean-field theory. An observed discrepancy of about 15% between the calculated and measured saturation values of the spontaneous magnetization can be explained by the presence of quadrupolar interactions.

Muon spin relaxation in presence of quadrupolar interactions

Muon spin relaxation in presence of quadrupolar interactions

Coupled nuclear and electronic spin wave modes in the presence of quadrupolar interaction

An investigation is presented of the coupled magnetic excitations which occur when a lattice of magnetically ordered localized electronic spins is in interaction with the corresponding nuclear spins via hyperfine and quadrupolar coupling. Of particular interest are systems with spin order incommensurate with the lattice, as found in certain rare earth metals. Magnetic resonance is considered and it is found that RF fields of small wavevector excite, with essentially electronic strength, coupled modes whose frequencies are related to the hyperfine and quadrupolar coupling constants. In a metal the broadening of these resonances is expected to be due mainly to skin depth effects.