Nuclear and Electron Resonance Study of the Paramagnetic Cobalt Ion

Magnetic resonance of the ${\mathrm{Co}}^{59}$ nucleus has been studied in Co${\left(\mathrm{N}{\mathrm{H}}_4\right)}_2$ ${\left(\mathrm{S}{\mathrm{O}}_4\right)}_2$·6${\mathrm{H}}_2$O, a material in which the Kramers ${\mathrm{Co}}^{2+}$ ion is strongly paramagnetic. The experiments were performed on shaped samples with the electronic moments of the ions aligned by a large applied magnetic field (40 to 80 kG) at low temperature (1.2°K). In addition to providing a measurement of the hyperfine and quadrupole interactions, the experiments yielded a determination of the interaction of the nucleus with the electronic moment that is induced by the external field. This coupling, which is related to the temperature-independent Van Vleck paramagnetism, was found to be anisotropic, having the magnitude ${\sigma }_{\parallel }=0.38\mathrm{}\pm 0.02$ and ${\sigma }_{\perp }=0.18\mathrm{}\pm 0.05$ as compared with the size of the normal Zeeman interaction of the nucleus with the applied field. A theoretical calculation of this interaction using the estimated crystal-field levels of ${\mathrm{Co}}^{2+}$ in the cobalt ammonium sulfate is in satisfactory agreement with experiment. Electron spin resonance measurements were also performed to obtain information of various parameters required for accurate calculations from the NMR data. The influence of hyperfine interactions on the spin-spin coupling among ions was also observed and is discussed.