Nuclear Magnetic Resonance and Relaxation ofAu197in Gold Metal andAg109in Gold-Silver Alloys

Abstract

The nuclear magnetic resonance (NMR) of ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ has been observed for the first time. Transient NMR experiments on metallic gold in the temperature range 1-4°K, and in external magnetic fields near 57 kOe, gave a frequency-to-field ratio $\frac{{\nu }^{\mathrm{}\left(197\right)\mathrm{}}}{\mathrm{H}}=0.074119\mathrm{}\left(4\right)\mathrm{}$ kHz/Oe, a spin-echo phase-memory time $T_2\approx 2$ msec, and spin-lattice relaxation times $T_1$ which are inversely proportional to the absolute temperature $T$ with $T_{1}T=4.6\mathrm{}\pm 0.4$ sec °K. Comparison of the experimental $\frac{{\nu }^{\mathrm{}\left(197\right)\mathrm{}}}{H}$ ratio with recent atomic-beam resonance measurements of ${\mu }^{\mathrm{}\left(197\right)\mathrm{}}$ leads to a Knight shift in gold metal $K=+(1.64\mathrm{}\pm 0.02)\%$. Results of related measurements on ${}_{}{}^{109}{}_{}{}^{}\mathrm{Ag}$ in ${\mathrm{Ag}}_x{\mathrm{Au}}_{1-x}$ alloys are also reported [$x=0.75:K=+(0.507\mathrm{}\pm 0.005)\%$, $T_{1}T=10.0\mathrm{}\pm 0.5$ sec °K; $x=0.50:K=+(0.454\mathrm{}\pm 0.010)\%$, $T_{1}T=13.6\mathrm{}\pm 0.8$ sec °K; $x=0.25:K=+(0.416\mathrm{}\pm 0.010)\%$, $T_{1}T=15.2\mathrm{}\pm 1.0$ sec °K; $x=0.05:K=+(0.392\mathrm{}\pm 0.010)\%$, $T_{1}T=17\mathrm{}\pm 1$ sec °K]. Magnetic-field measurements in these experiments were based on a silver-metal reference for which a direct comparison of the 4°K ${}_{}{}^{109}{}_{}{}^{}\mathrm{Ag}$ NMR frequency with the room-temperature frequency of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ in heavy water yielded $\frac{{\nu }^{\mathrm{}\left(109\right)\mathrm{}}}{H}=0.199133\mathrm{}\left(4\right)\mathrm{}$ kHz/Oe. The measured Knight shifts and spin-lattice relaxation rates are used to estimate the exchange enhancements of the respective static conduction-electron spin susceptibilities, as well as the ratios of the average contact hyperfine fields in the metals to those in the corresponding free atoms.