Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 11: New Instruments and Methods

CPP 11.3: Talk

Tuesday, March 27, 2012, 10:15–10:30, C 243

A numerical approach to macroscopic nuclear spin-lattice relaxation by paramagnetic impurities — •Simon Quittek, Michael Ditter, and Franz Fujara — Institut für Festkörperphysik, TU Darmstadt

The influence of paramagnetic impurities on the nuclear spin-lattice relaxation rate has been known for about fifty years. Good heat contact between both systems favors a relaxation path from the nuclei via the impurities into the lattice, which considerably speeds up the bulk relaxation.

Whereas microscopic theory is well investigated, we lack a detailed understanding of the macroscopic processes. Recent field-cycling NMR data reveil a field dependence of the relaxation rate that is not comprised by conventional methods.

To shed some light onto this up-to-date problem, a computer simulation has been performed. The combined relaxation-diffusion equation is solved ab initio in a deterministic numeric scheme, which discretizes the considered space. An alternative approach maps the diffusion component onto random walkers, which in turn carry magnetization that is gradually lost when approaching an impurity.

The calculations yield relaxation behaviour that is in good agreement with experimental data. Impurity distributions and magnetic fields are reflected in the field dependent relaxation rates.