Temperature dependence of electric field gradient and Knight shift in Mg

Abstract

The hyperfine properties of Mg such as Knight shift and electric field gradients (EFG) have been calculated from first principles as a function of temperature. The conduction-electron wave functions were obtained in the orthogonalized-plane-wave model by taking into account both the thermal expansion of the lattice and the effect of thermal vibrations of the ions on the crystal - field potential. The decrease in the ${p}_{x}\ensuremath{-}{p}_{y}$-like and ${p}_{z}$-like electrons with temperature leads to a decrease in the conduction-electron contribution to EFG. The lattice contribution is found to be rather insensitive to temperature and the conduction-electron part is largely responsible for the observed ${T}^{\frac{3}{2}}$ temperature dependence of the EFG. The decrease in the $p$ content of the wave function with temperature is accompanied by a simultaneous increase in the $d$ content and, to a small amount, of the $s$ content of the wave function. This small rise in the $s$-like electrons makes the Knight shift less dependent upon temperature than the EFG---an observation consistent with experimental data.