Nuclear magnetic resonance in liquid metals and alloys

Abstract

Nuclear magnetic resonance in metals both above and below the melting point is dominated by the hyperfine interaction with the conduction electrons. The principal effect is due to the direct contact interaction, with smaller, but significant, contributions from the indirect core-polarisation term and from orbital effects. In metals and alloys of nearly free electron character, the contact term gives rise to an almost temperature independent shift of the resonant frequency and a relaxation rate which is proportional to the absolute temperature. The measurement of the frequency shift in liquid metals and binary alloy is traced and the extent to which the pseudopotential theory of the metallic state is able to predict the shift and the way it depends on temperature and composition in alloys is discussed. The nearly free electron model is not a satisfactory description of the liquid semiconductors and in these materials the behaviour of the nmr is markedly different, becoming related to the electron transport. The relationship between the frequency shifts and relaxation rates in liquid semiconductors and related materials and the various theoretical models is indicated. Finally, the substantial quadrupolar contribution to the relaxation rate in the heavy polyvalent materials and its relationship with the time-dependence of the spatial distribution of the atoms in liquid metals is described.