Magnetic Properties and Structure of Cobalt Hardened Gold

The iq-hmziitation of an experimental design to investigate the variation in cobalt hardened gold electrodeposition produced a series of electrodeposited AuCo alloys which had been stripped from their copper substrates. The magnetic properties of these electroplatings were measured at room temperature using the Faraday method. These measurements showed the presence of two magnetic phases. One phase consisted of a solid solution of cobalt in the gold matrix and the second was found to be a diamagnetic cobalt containing component. The magnetic measurements showed that no precipitates of metallic cobalt were present and that individual atoms and nearest neighbor pairs of cobalt atoms in the solid solution are not magnetic. The diamagnetic phase cannot contain cobalt hexacyanocobaltate Co,(Co(CN),),, which is found after treatment of the alloy with aqua regia. Also,the second phase can not all be potassium hexacyanocobalte K3(Co(CN)J. Subsequent to this the platings were annealed in hydrogen at 800" C to destroy any cobalt compounds in the platings and the magnetic properties were remeasured. These second measurements showed the existence of only one phase, again a solid solution of cobalt in gold. This phase showed superparamagnetic behavior with some remanence and is a magnetic nanocomposite. The amount of the cobalt in the "metallic" and "compound" phase is calculated from the contribution of each phase to the initial slope of the magnetization curve.