Determination of the nature of fluctuations using ${}^{8}Li$ and ${}^{9}Li$ $\beta$-NMR and spin-lattice relaxation

We report a comparison of the $1\mathrm{/}{T}_1$ spin lattice relaxation rates (SLR) for ${}^{9}Li$ and ${}^{8}Li$ in Pt and SrTiO${}_3$, in order to differentiate between magnetic and electric quadrupolar relaxation mechanisms. In Pt, the ratio of the $1\mathrm{/}{T}_1$ spin relaxation rates $R_{Pt}$ was found to be 6.82(29), which is close to but less than the theoretical limit of $\sim 7.68$ for pure magnetic relaxation. In SrTiO${}_3$ this ratio was found to be 2.7(3), which is close but larger than the theoretical limit of $\sim 2.14$ expected for pure electric quadrupolar relaxation. These results bring new insight into the nature of the fluctuations in the local environment of implanted ${}^{8}Li$ observed by $\beta$-NMR.