β-detected nuclear quadrupole resonance and relaxation of 8Li+ in sapphire

Z Salman,M R Pearson,K H Chow,D Wang,T J Parolin,M D Hossain,C D P Levy,W A Macfarlane,H Saadaoui,R F Kiefl

doi:10.1088/1742-6596/551/1/012034

Abstract

We report detailed behaviour of low energy 8Li implanted near the surface of α- Al2O3 single crystal, as revealed by beta-detected NQR of 8Li. We find that the implanted 8Li occupies at least two sites with non-cubic symmetry in the Al2O3 lattice. In both sites the 8Li experiences axially symmetric electric field gradient, with the main principal axis along the c-crystallographic direction. The temperature and field dependence of the spin lattice relaxation of 8Li in α-Al2O3, indicate that the 8Li diffusion is negligible on the scale of its lifetime, 1.21 s.

Highlights

Sapphire (α-Al2O3) is an important material with many technological applications, for example in optoelectronics, catalysis and environmental chemistry [1]
The temperature and field dependence of the spin lattice relaxation rate indicate that the main source of spin relaxation of 8Li in Al2O3 is fluctuations of the electric field gradient (EFG). These results rule out 8Li diffusion in sapphire, even near its surface at and below 300 K
We tried to measure β-NQR spectra, while implanting 8Li with its polarization perpendicular to the c-axis of the Al2O3 crystal. Under these conditions there was no measurable asymmetry in zero field (ZF), possibly due to (i) all the implanted 8Li occupy a site with a very small nuclear quadrupole interaction, (ii) the main principal axis (MPA) at 8Li site is along the c-axis, or (iii) a large η which produces a large mixing between the different |m states and a subsequent loss of polarization

Summary

Introduction

Sapphire (α-Al2O3) is an important material with many technological applications, for example in optoelectronics, catalysis and environmental chemistry [1]. In this paper we present zero magnetic field β-detected nuclear quadrupole resonance (βNQR) of 8Li+ implanted near the surface of sapphire. The magnetic resonance is detected by monitoring the time-averaged nuclear polarization as a function of a small radio frequency (RF) magnetic field applied perpendicular to the initial polarization direction.

Results

Conclusion