Relaxation (NMR)

About: Relaxation (NMR) is a research topic. Over the lifetime, 29342 publications have been published within this topic receiving 689851 citations.

Use of the Adam‐Gibbs Equation in the Analysis of Structural Relaxation

Abstract: Narayanaswamy's model of structural relaxation has been shown to provide an excellent description of the behavior of a variety of glasses. In the standard formulation, the relaxation time, τ is represented by the Arrhenius equation, with the activation energy partitioned between the temperature and Active temperature. That form for τ is successful, but lacks theoretical justification. In this paper, the Adam-Gibbs equation is shown to describe accurately both τ and the viscosity of NBS 710 (alkali lime silicate) glass. This equation is expected to be accurate over a wider range of temperature and Active temperature than the Arrhenius equation.

Molecular dynamics and the phase transition in solid C 60

Abstract: We characterize the molecular reorientational dynamics in two phases of solid ${\mathrm{C}}_{60}$ with $^{13}\mathrm{C}$ NMR measurements. A change in the nature of the dynamics, indicated by a change in kinetic parameters extracted from spin-lattice relaxation data, occurs at the phase transition at 260 K. Above the transition, the molecules appear to execute continuous rotational diffusion; below the transition, they appear to jump between symmetry-equivalent orientations. This interpretation is consistent with the x-ray-diffraction results of Heiney et al. as well as our NMR relaxation and spectral data.

Rotary resonance recoupling of dipolar interactions in solid‐state nuclear magnetic resonance spectroscopy

Abstract: A new resonance effect in solid‐state nuclear magnetic resonance (NMR) is described. The effect involves a combination of magic‐angle sample rotation with irradiation of a heteronuclear spin system at the Larmor frequency of one of the spin species. If the irradiation intensity is such as to establish a match between spin nutation and sample rotation, it is shown that the heteronuclear dipolar spin interaction is selectively reintroduced into the spectrum. This allows small dipolar coupling constants to be measured in the presence of large shielding anisotropies. Applications are anticipated for determination of internuclear distances in materials lacking long‐range order, such as polycrystalline materials, polymers, and surfaces.

Distorted MnIVMnIII3 Cubane Complexes as Single-Molecule Magnets

Abstract: Alternating current (ac) magnetic susceptibility data are presented for six distorted cubane complexes of the composition [MnIVMnIII3O3X] Each of these complexes has a well isolated S = 9/2 ground state There is zero-field splitting (ZFS) in the ground states where D, the axial ZFS parameter, is found to be in the range of −027 to −038 cm-1 As a result of the big spin ground state and appreciable magnetic anisotropy, an out-of-phase ac magnetic susceptibility signal is seen for each of the six Mn4 complexes The out-of-phase ac susceptibility signal reflects slow magnetization relaxation which is taken to indicate that individual molecules are acting as magnets Alternating current susceptibility data are presented for a frozen glass of one of the Mn4 complexes to confirm that the out-of-phase ac signal is associated with isolated molecules The factors that influence whether a given complex can function as a single-molecule magnet are described The above Mn4 complexes represent only the second type