Low-temperature nuclear spin-lattice relaxation in glasses - homogeneous and inhomogeneous averaging |
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Authors: | H.-J Stöcmann P Heitjans |
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Affiliation: | Fachbereich Physik, Universität Marburg, 3550 Marburg, W. Germany |
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Abstract: | A phenomenological model is presented which is able to explain both temperature and magnetic field dependences of nuclear spin-lattice relaxation rates T1?1 observed recently in glasses at low temperatures. The model assumes randomly distributed defect centres, typical of glasses, producing internal fluctuating fields. The only restrictive assumption is a power law for the distance dependence of the responsible interaction. In accordance with experiment, homogeneous and inhomogeneous relaxation, corresponding to exponential and non-exponential relaxation behaviour, is predicted in the cases of rapid and slow spin diffusion, respectively. Describing the fluctuating interactions by a BPP-type spectral density and assuming an Arrhenius law for the correlation time, explicit expressions for T-1? are obtained. It is shown that by comparison of homogeneous and inhomogeneous relaxation data information on the type of interaction and the density of defect centres can be obtained. |
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