Line shapes of multiple quantum NMR coherences in one-dimensional quantum spin chains in solids

Orientational dependencies of dynamics and relaxation of multiple quantum NMR coherences in one-dimensional systems

Dynamics and relaxation, or decoherence, of multiple quantum (MQ) coherences are investigated experimentally and theoretically for different orientations of a single crystal of fluorapatite with respect to the external magnetic field. Dynamics of MQ coherences is studied as a function of the preparation period of the MQ NMR experiment. Their relaxation, or decoherence, during the evolution period is also investigated. Universal curves for dynamics and relaxation are obtained and describe the experimental data for different orientations of the investigated sample. Those curves prove the dipolar nature of the observed relaxation process. The contribution of the heteronuclear interactions to the dipolar relaxation is also investigated. The source of discrepancies between experimental data and theoretical results in the experiments with a large angle between the nuclear spin chains and the external magnetic field are discussed.

Relaxation of Multiple Quantum NMR Coherences in Quasi-One-Dimensional Spin Systems

Dynamics and relaxation of the multiple quantum (MQ) NMR coherences of the zeroth and second orders are studied experimentally and theoretically in a quasi-one-dimensional chain of nuclear spins 19F in calcium fluorapatite. The dependencies of the intensities of those coherences on the time of the preparation period of the MQ NMR experiment is obtained. A good agreement of the experiment with theoretical predictions is demonstrated. Dipolar relaxation of the MQ NMR coherences is investigated on the evolution period of the MQ NMR experiment. A theory of dipolar relaxation of the MQ NMR coherences is developed for the model in which only the ZZ part of the secular dipole–dipole interactions is taken into account (ZZ model). It is shown that the MQ NMR coherence of the zeroth order is not subject to dipolar relaxation in the ZZ model. The experimental data qualitatively agree with the results of the developed theory for the MQ NMR coherence of the second order.