Pressure Dependence ofGa71andAu197Nuclear Magnetic Resonance in Pure and Pd-Doped AuGa2

Abstract

Nuclear-magnetic-resonance measurements have been made of the Knight shift $K$ and spin-lattice relaxation time $T_1$ of ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ in ${\mathrm{Au}}_{1-x}{\mathrm{Pd}}_x{\mathrm{Ga}}_2$ for $x=0.0, 0.012, \mathrm{and} 0.026$ as a function of hydrostatic pressure to 8.4 kbar and temperature $T$ in the range 4-300°K. The Knight shift for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ in Au${\mathrm{Ga}}_2$ was also measured as a function of pressure at 4 °K. Large increases for both the ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ shift and relaxation rate of Au${\mathrm{Ga}}_2$ were observed at 4 °K near 7 kbar pressure. The magnitudes of $K$ and ${\left(T_{1}T\right)}^{-1\mathrm{}}$ exhibited a decrease upon increasing $T$ at high pressure. In contrast, the ${}_{}{}^{195}{}_{}{}^{}\mathrm{Au}$ shift showed both pressure and temperature independence. The ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ Korringa product ($K^2{T}_{1}T$) was temperature and pressure dependent and provides evidence of appreciable electron-electron interactions at low temperatures. Increases for $K$ and ${\left(T_{1}T\right)}^{-1\mathrm{}}$ were also found at 4 °K in Pd-doped Au${\mathrm{Ga}}_2$. Compared to pure Au${\mathrm{Ga}}_2$, the "turn on" occurred at lower pressures and was more gradual, and the magnitude of the effect was smaller. We have interpreted these effects in terms of a band-structure-electron-transition picture, which involves a sharp peak in the density of states located 10-15 meV below the Fermi level at normal volume and absolute zero.