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Magnetically "tagged" nuclear relaxation in superionic conductors

Magnetically "tagged" nuclear relaxation in superionic conductors Introducing paramagnetic atoms into a superionic conductor may produce large, temperature-dependent effects on the transverse T 2 - 1 and longitudinal T 1 - 1 relaxation rates of the NMR of the nuclei of the diffusing ions. Such effects have been observed for the first time in a study of the F 19 NMR in Pb F 2 , substitutionally doped with Mn 2 + ions at concentrations c ranging from 0.01 to 1 mole%. The relaxation induced by the F 19 - Mn 2 + near-neighbor-transferred hyperfine interaction, I → · A ̃ · S → , results in a single peak in T 2 - 1 vs T and two peaks in T 1 - 1 vs T , with the rates proportional to c . A unified treatment of both the statistical aspects of the F - ion motion and the dynamical evolution of the F 19 magnetization during the encounters with the Mn 2 + spins is given within the framework of an "impact" model theory. This approach is contrasted with an earlier perturbative treatment by Richards and is shown to differ from it in several important respects. With the help of recently measured values of A ̃ for Mn 2 + in Pb F 2 and estimates of the Mn 2 + electronic spin-lattice relaxation obtained from EPR studies, a comparison between theory and experiment is made. Agreement is found at all but the highest temperatures for T 2 - 1 , indicating a larger spectral density of low-frequency fluctuations than is expected. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review B American Physical Society (APS)

Magnetically "tagged" nuclear relaxation in superionic conductors

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Publisher
American Physical Society (APS)
Copyright
Copyright © 1981 The American Physical Society
ISSN
1095-3795
DOI
10.1103/PhysRevB.24.3756
Publisher site
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Abstract

Introducing paramagnetic atoms into a superionic conductor may produce large, temperature-dependent effects on the transverse T 2 - 1 and longitudinal T 1 - 1 relaxation rates of the NMR of the nuclei of the diffusing ions. Such effects have been observed for the first time in a study of the F 19 NMR in Pb F 2 , substitutionally doped with Mn 2 + ions at concentrations c ranging from 0.01 to 1 mole%. The relaxation induced by the F 19 - Mn 2 + near-neighbor-transferred hyperfine interaction, I → · A ̃ · S → , results in a single peak in T 2 - 1 vs T and two peaks in T 1 - 1 vs T , with the rates proportional to c . A unified treatment of both the statistical aspects of the F - ion motion and the dynamical evolution of the F 19 magnetization during the encounters with the Mn 2 + spins is given within the framework of an "impact" model theory. This approach is contrasted with an earlier perturbative treatment by Richards and is shown to differ from it in several important respects. With the help of recently measured values of A ̃ for Mn 2 + in Pb F 2 and estimates of the Mn 2 + electronic spin-lattice relaxation obtained from EPR studies, a comparison between theory and experiment is made. Agreement is found at all but the highest temperatures for T 2 - 1 , indicating a larger spectral density of low-frequency fluctuations than is expected.

Journal

Physical Review B – American Physical Society (APS)

Published: Oct 1, 1981

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