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Nuclear magnetic resonance study of single crystals of gallium metal Valic, Marko Ivan

Abstract

The nuclear magnetic resonance spectrum of gallium metal has been investigated in single crystal specimens in both low and high magnetic fields from 4.2°K to the melting point (T[subscript MP] = 300°K) and then extended to the liquid phase. Precise determinations for the two non-equivalent nuclear sites have been made of (a) the electric field gradient (EFG) tensor and (b) the Knight shift (K) tensor. The relationship of these results to the crystal structure of gallium metal is discussed in detail. The isotopic Knight shift in the solid, K[superscript sol; subscript iso] increases linearly with temperature from (0.132±0.004)% at 4.2°K to (0.155±0.004)% just below T[subscript MP]. In the liquid, just above T[subscript MP], K[superscript liq; sucscipt iso] = (0.453±0.003)% and decreases very slowly with increasing temperature. These results are discussed in terms of the Korringa relations in the solid and liquid phases, respectively. Implications of these results are developed with regard to changes in the electronic structure of gallium upon melting. The angular dependence of K[subscript an] agrees with the predicted angular dependence for the Knight shift anisotropy in an orthorhombic environment and is described with two anisotropy parameters defined as K₁ and K₂. No K- anisotropy is found along the Y (B crystal) axis. The principal axes of the K tensor have different signs from the quadrupolar principle axes. K[subscript an] (X) is found to be very large, i.e. K[subscript an] (X)/K[subscript iso] = -18% at 77°K, and temperature dependent. Increasing the temperature (T) from 4.2°K, K[subscript an] (X) increases to a maximum at 77°K and then slowly decreases as T approaches T[subscript MP] where it still retains a large value. This paradoxical behaviour is assumed to be a result of particular and unusual details of the gallium Fermi surface.

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