Hyperfine fields in a Ag/Fe magnetic multilayer probed with low energy spin polarized 8Li

A beam of low energy Li8 has been used to probe the hyperfine field distribution in a magnetic multilayer composed of Au(4nm)/Ag(80nm)/Fe(2nm) grown on a GaAs substrate. The β-NMR frequency spectrum is shown to be a strong function of the implantation energy reflecting the depth dependence of the local hyperfine fields. Correlating the spectra with TRIM.SP implantation profiles allows us to identify signals from the GaAs, Ag and Au layers. The frequency spectrum in Ag is a strong function of energy. A very narrow line, and corresponding distribution of hyperfine fields, is observed when the beam in centered well away from the Fe whereas a much broader distribution is observed when the Li stops close to the Fe. These results demonstrate that low energy β-NMR can act as a sensitive probe of the induced magnetism in the otherwise non-magnetic Ag spacer layers.