The influence of pH and bath composition on the properties of Ni–Co coatings synthesized by electrodeposition

Ni–Co coatings were produced on Cu substrates by electrodeposition from electrolytes with different pH values and different Co2+ concentration. The current efficiency increases from 52.1% to 81.2% with the pH increasing from 2.0 to 5.4. It is clearly observed that the content of cobalt in the deposited coatings gradually increases from 9.4% to 19.6% as the pH value varies from 2.0 to 5.4. The Co content in the deposited coatings increases from 16.5% to 72.7% as the molar ratio of CoSO4/NiSO4 varying from 1:5 to 1:2 in electrolyte. XRD patterns reveal that the structure of the coatings strongly depends on the Co content in the binary coatings. Both granular and dendritic crystals were investigated by SEM and the different crystallization behaviors were illustrated. The saturation magnetization of the coatings goes up from 96.36 kAm−1 to 136.08 kAm−1 with the pH value increasing from 2.0 to 5.4. The saturation magnetization (Ms) and coercivity (Hc) move up from 144.84 kAm−1 and 15.27 kAm−1 to 175.13 kAm−1 and 125.20 kAm−1 with the increase of Co in the electrolyte, respectively.

► The influence of pH was in-depth discussed and calculated.
► Granular and dendritic crystals were investigated.
► Anodic process of the cyclic voltammograms was investigated.