NMR Determination of the Conduction-Electron Hyperfine Interaction in Crystalline CdO

Measurements of the ${\mathrm{Cd}}^{113}$ nuclear-spin-lattice relaxation time $T_1$ and Hall effect in crystalline CdO, a degenerate semiconductor, have yielded the contact hyperfine strength of the conduction electrons at the nuclei. The product $T_{1}T=168\mathrm{}$ sec °K, independent of temperature $T$ and frequency $\nu$ for $T=1.4,4.2, \mathrm{and} 77-350$ °K, and for $\nu =2\mathrm{}-10$ MHz. Taking the carrier concentration $N=2.6\mathrm{}\times {10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$ independent of temperature to within 3% at 4.2, 77, and 300°K, and using an effective electron mass $m_e^{}{}_{}{}^{*}=0.2\mathrm{}{m}_e$, we calculate an averaged electron probability density at the nucleus, $〈{\left|{\phi }_F\mathrm{}\right(0\left)\right|}^2〉=7\mathrm{}\times {10}^{25}$ ${\mathrm{cm}}^{-3\mathrm{}}$, normalized to unity in an atomic volume. A comparison with $〈{\left|{\phi }_{\mathrm{A}}\mathrm{}\right(0\left)\right|}^2〉$ in an isolated atom is interpreted to show that the Fermi level of the impurity band lies in the host-lattice conduction band. The Hall-effect data support this. The resonance frequency shift predicted from the Korringa relationship, -0.017%, is smaller than the observed shift, -0.031%. This is thought to be due to covalency contributions rather than to electron-electron interactions.