Electroless polyol synthesis and properties of nanostructured NixCo100−x films

A non-aqueous, electroless, polyol process was used to deposit nanostructured NixCo100−x films on Cu substrates by reducing nickel acetate and cobalt acetate in refluxing ethylene glycol at 194°C for 1 h. As-deposited films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), microhardness and microscratch tests. The films had a (1 1 1) texture and the average crystallite size increased with x from 15 to 64 nm. The films showed in-plane magnetization anisotropy. Saturation magnetization (Ms) increased with increasing Co concentration and reached 1421 emu/cm3 for Co100. The perpendicular coercivity (Hc⊥) was higher than that in-plane (Hc). The Ni50Co50 film had the highest Hc⊥ and microhardness compared to other films of different compositions. The critical load for delamination increased with x and was independent of film thickness. In this polyol process film deposition on the substrate competed with undesirable powder precipitation in the solution. Lowering the reaction temperature did not favor film deposition. However, film deposition occurred when an electric field was applied during the reaction at temperature as low as 100°C. Precipitation of colloidal particles persisted at this low temperature in a different diol.