Comparison of ⁸Li and ⁹Li Spin Relaxation in SrTiO₃ and Pt: A Means to Distinguish Magnetic and Electric Quadrupolar Sources of Relaxation

Abstract

We demonstrate that the ratio of 1/T 1 spin-lattice relaxation rates (SLR) of two different isotopes (here 8 Li and 9 Li) can be used in order to identify the predominant relaxation mechanism within the β-NMR technique. We studied with both isotopes a Pt foil and two samples of single crystal SrTiO 3. In Pt, the ratio of the SLR rates was 6.82(29), which is close to but less than the theoretical limit of ∼ 7.68 for pure magnetic relaxation. In SrTiO 3 , the weighted averaged SLR ratio of the two samples was 2.7(3), which is close but larger than the theoretical limit of ∼ 2.14 expected for pure electric quadrupolar relaxation. This indicates that the primary source of relaxation in SrTiO 3 is electric quadrupolar in origin and that magnetic effects have a much smaller importance in this material. The low effective asymmetry of 9 Li was the dominant cause of uncertainty of the measurements in this study. We propose a system of tagging the beta-decays in coincidence with the alpha decays that take place in two of the three primary decay channels of 9 Li as a way of increasing the effective asymmetry and enhance the signal of 9 Li β-NMR.