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Nuclear magnetic resonance in single crystals of tin and cadmium. Sharma, Surendra Nath

Abstract

A systematic study of the Knight shift parameters has been carried out on single crystal specimens of tin and cadmium over a range from 1⁰ K to just below the melting points. The line widths observed in cadmium are approximately half the widths quoted by other workers, enabling more precise measurements to be made. These measurements show that the anisotropy of the Knight shift in cadmium changes sign between 4⁰ K and 77⁰ K. Pronounced changes in the Knight shift parameters are observed upon alloying cadmium with mercury. The temperature dependence of the isotropic Knight shift in tin can be explained by the volume effects and the phonon contributions when the temperature exceeds the Debye temperature. Comparing the temperature dependence data with pressure dependence results of other workers the explicit temperature dependence is extracted. It appears that the variation in the anisotropy of the Knight shift above the Debye temperature is largely caused by a change in lattice parameters, specifically a change in c/a ratio. Measurements of the line width at helium temperature in isotopically pure Sn¹¹⁹ and the same isotope in natural tin as a function of crystal orientation are reported. Second moments for the different crystal orientations have been computed. Analysis of the isotopically pure tin data leads to an evaluation of relative contributions, from the various shells, to the pseudo-dipolar interaction. For the isotopically pure tin, the measurements at the helium and room temperatures enable an evaluation of the spin-lattice relaxation time, T₁. T₁T is constant over the temperature range and closely isotropic.

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