New method for the determination of the sign and magnitude of electric quadrupole splittings. II. The electric field gradient of Co in hcp and fcc Co

The 0°-90° differential resonance displacement $\overline{\Delta \nu }=\overline{\nu \mathrm{}\left(0\right)\mathrm{}}-\overline{\nu \mathrm{}\left(90\right)\mathrm{}}$ and the 0° total resonance displacement $\overline{\nu \mathrm{}\left(0\right)\mathrm{}}-{\nu }_M$ of the NMR-ON (oriented nuclei) resonances of ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ in hcp Co have been measured at a temperature $T=10\mathrm{}\left(1\right)\mathrm{}$ mK as +57(6) kHz and +0.44(9) MHz, respectively. Using the relations ${\nu }_Q=c_1\overline{\Delta \nu }$ and ${\nu }_Q=c_2(\overline{\nu \mathrm{}\left(0\right)\mathrm{}}-{\nu }_M)$, where $c_1$ and $c_2$ are calculable constants, the quadrupole splitting ${\nu }_Q=\frac{e^2\mathrm{qQ}}{h}$ is deduced as -3.1(4) MHz. In combination with NMR data on ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}\mathrm{Co}$ (hcp) the electric field gradient (EFG) in hcp Co is found to be -0.30(3)×${10}^{17}$ V/${\mathrm{cm}}^2$. The negative sign supports the correlation of EFG's in hcp transition metals reported recently. For ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}\mathrm{Co}$ (fcc) a small positive quadrupole splitting ${\nu }_Q=+0.75\mathrm{}\left(39\right)\mathrm{}$ MHz was observed.