${}^{207}\mathrm{Pb}$ spin-lattice relaxation in solid ${\mathrm{PbMoO}}_4$ and ${\mathrm{PbCl}}_2$

We have measured the ${}^{207}\mathrm{Pb}$ nuclear spin-lattice relaxation rate $R$ as a function of temperature $T$ at two nuclear magnetic resonance frequencies ${\omega }_0$ in the ionic solids lead molybdate $\left({\mathrm{PbMoO}}_4\right)$ and lead chloride $\left({\mathrm{PbCl}}_2\right)$. $R$ is unexpectedly large, proportional to $T^2$, and independent of ${\omega }_0$. Taken together with previous work in lead nitrate $\left[\mathrm{Pb}\right({\mathrm{NO}}_3{)}_2]$, these results show that the relaxation does not depend on the nature or rotational motion of the counterion, particularly since the counterion in lead chloride is a single chlorine atom. The theory that explains the observed relaxation rate is reviewed. A second-order Raman process dominates the observed relaxation process. It involves the modulation of the spin-rotation interaction by the lattice vibrations.

Figure 1

The solid state ${}^{207}\mathrm{Pb}$ spin-lattice relaxation rate $R$ vs $T^2$ for ${\mathrm{PbMoO}}_4$ ($●62.6\mathrm{MHz}$, $∎41.7\mathrm{MHz}$) and ${\mathrm{PbCl}}_2$ ($▾62.6\mathrm{MHz}$, $▴41.7\mathrm{MHz}$). The dashed line summarizing the data for $\mathrm{Pb}({\mathrm{NO}}_3{)}_2$ is taken from Ref. 3.