β-NMR of isolated 8Li+ implanted into a thin copper film

Depth-controlled beta-NMR was used to study highly spin-polarized Li-8(+) in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive Knight shifts and spin relaxation data show that Li-8(+) occupies two sites at low temperatures, assigned to be the substitutional (S) and octahedral (O) interstitial sites. Between 50 and 150 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.