  Recently high density (HD) nonmagnetic (NM) cobalt has been discovered in a
cobalt thin film, grown on Si(111). This cobalt film had a natural cobalt oxide
at the top. The oxide layer forms when the film is taken out of the
electron-beam deposition chamber and exposed to air. Thin HD NM cobalt layers
were found near the cobalt/silicon and the cobalt-oxide/cobalt interfaces,
while the thicker mid-depth region of the film was hcp cobalt with normal
density and normal magnetic moment. If an ultrathin film of gold is grown on
the cobalt layer, before exposing it to air, the oxidation of the cobalt
surface layer is prevented. It is important to investigate whether the growth
of HD NM cobalt layers in the thin film depends on (i) capping of the film by
the gold layer, (ii) the film thickness and (iii) the nature of the substrate.
The results of such investigations, presented here, indicates that for cobalt
films capped with a thin gold layer, and for various film thicknesses, HD NM
cobalt layers are still observed. However, instead of a Si substrate, when the
cobalt films are grown on oxide substrates, such as silicon oxide or cobalt
oxide, HD NM cobalt layers are not observed.
