Impurity Knight Shift and Electric Field Gradients at Al Nuclei in Dilute Substitutional Al-Li Alloys

Abstract

After a brief summary of the necessary notions of nuclear magnetic resonance, we present results for the contact spindensities at a substitutional Li nucleus, and for the electric field gradient caused by the impurity at the first three nearest neighbour host nuclei in a dilute Al-Li alloy. The displaced charge-and spin-densities around the impurity are computed selfconsistently using the spin-density functional formalism and including the main effect of the discreteness of the lattice. The latter is seen to play an essential role in determining the phase of the Friedel oscillations (and therefore the electric field gradient) and the impurity Knight shift. Due to the presence of polarizable bound states, the conventional formula for the Knight shift $K \sim < \left| {\psi _k^ \to } \right.{\left. {\left( 0 \right)} \right|^2}{ > _{FS}}$ is found to be inadequate.