High density nonmagnetic cobalt in thin films

TL;DR

This study investigates the formation of high-density nonmagnetic cobalt layers in thin films, showing that capping with gold and substrate type influence their presence, with potential implications for magnetic and electronic properties.

Contribution

It demonstrates that high-density nonmagnetic cobalt layers can form in thin films regardless of gold capping and film thickness, but are absent on oxide substrates, revealing substrate and capping effects.

Findings

HD NM cobalt layers are present with gold capping across various thicknesses.

HD NM cobalt layers are absent on oxide substrates.

Gold capping prevents surface oxidation of cobalt.

Abstract

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.