Determination of the nature of fluctuations using Li8 and Li9β -NMR and spin-lattice relaxation

Abstract

We report a comparison of the 1/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/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 ∼ 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 ∼ 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 β -NMR.

Microscopic Dynamics of Li+ in Rutile TiO2 Revealed by 8Li β-Detected Nuclear Magnetic Resonance

“…It represents the spin relaxation of all the 8 Li in the sample, not only those corresponding to measurable resonances. SLR rates in rutile were measured from 5-300 K under applied magnetic fields of: 1.90 T and 6.55 T parallel to the TiO 2 (100); and 10 mT and 20 mT perpendicular to the TiO 2 (100).…”

“…The spin of any onresonance 8 Li is precessed rapidly by the RF field, resulting in a loss in time-averaged asymmetry. The evolution of the resonance was recorded over a temperature range of 10 K to 315 K with a highly-homogeneous magnetic field of 6.55 T parallel to the TiO 2 (100). The resonance frequency was calibrated against that in single crystal MgO (100) at 300 K, 51 with the superconducting solenoid persistent.…”

“…The character of the relaxation (magnetic, quadrupolar or mixed) can also be tested by comparison with another Li isotope, such as the spin 3/2 9 Li as has been recently demonstrated. 100 It is important to recall that the amplitude of the relaxing signal is temperature independent even at low field, meaning that we do not have a fraction of the signal that is so fast relaxing that it is lost (wiped out) as has been seen in 7 Li NMR from polarons in the perovskite Li 3x La 2/3−x TiO 3 . 98 Thus if a significant fraction of 8 Li + forms the bound complex here, then its relaxation remains measurable even at low field.…”

“…9A, the axis of the two nearestneighbour oxide ions alternates from one site to the next along c by 90 • . Beyond the first coordination, there are two nearest neighbour Ti on opposite sides, and the Ti−Li−Ti direction also alternates between [100] and [010] along the channel, shown in Fig. 9B.…”

“…98 Thus if a significant fraction of 8 Li + forms the bound complex here, then its relaxation remains measurable even at low field. are two nearest neighbour Ti on opposite sides, and the Ti−Li−Ti direction also alternates between [100] and [010] along the channel, shown in Fig. 9B.…”