The Site and High Field βNMR Properties of ⁸Li⁺ Implanted in α-Al₂O₃

Abstract

We present high (> 2 T) magnetic field βNMR measurements of 8Li+ implanted in single crystals of sapphire, a commonly used backing material for other samples. From the well-resolved quadrupolar splitting, we extract the electric field gradient (EFG) at the implanted 8Li+ site. Comparison with supercell density functional theory calculations of the EFG allows us to identify the octahedral interstitial site as the most likely candidate. In contrast to the zero field βNQR spectra, where multiple singals are detected, only a single site is evident at high field. We discuss possible explanations for this discrepancy. The spin lattice relaxation is extremely slow (1/T 1 < 0.02 s−1 ) over a broad temperature range from 4 to 300 K, demonstrating that cross relaxation with the 27Al nuclear spins is quenched in such high magnetic fields.

SRF material research using muon spin rotation and beta-detected nuclear magnetic resonance

“…Its strength depends on the details of the coupling to the host spins. When nuclear moments are absent or very low in magnitude, this regime can be restricted to quite low fields, for example, in Au (MacFarlane et al, 2018), but in other cases with a high density of large moment nuclei, such as Al 2 O 3 (MacFarlane et al, 2023) or Nb, it can extend up to several kG. While cross-relaxation also occurs for the implanted muon, the dynamics of nuclear spins are usually sufficiently slow, that they can be treated as static during the muon lifetime (see Section 2.2), and one simply gets depolarization due to Frontiers in Electronic Materials frontiersin.org precession in the static random nuclear dipolar fields, for example, Eq.…”