$\beta$-NMR of Isolated $^{8}$Li$^{+}$ Implanted into a Thin Copper Film

TL;DR

This study uses depth-controlled $eta$-NMR to investigate the behavior of highly spin-polarized $^8$Li in a thin copper film, revealing site occupation and temperature-dependent site changes consistent with metallic properties.

Contribution

It provides detailed insights into the site occupation and temperature-dependent behavior of $^8$Li in copper using depth-controlled $eta$-NMR, a novel application for this system.

Findings

$^8$Li occupies substitutional and interstitial sites at low temperatures.

A site change from octahedral to substitutional occurs between 50-100 K.

High-temperature behavior follows the Korringa Law for simple metals.

Abstract

Depth-controlled $\beta$-NMR was used to study highly spin-polarized $^8$Li in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive Knight Shifts and spin relaxation data show that $^8$Li occupies two sites at low temperatures, assigned to be the substitutional ($S$) and octahedral ($O$) interstitial sites. Between 50 to 100 K, there is a site change from $O$ to $S$. The temperature dependence of the Knight shifts and spin-lattice relaxation rates at high temperatures, i.e. when all the Li are in the $S$ site, is consistent with the Korringa Law for a simple metal.