Electrochemical nucleation behaviours and properties of electrodeposited Co–Ni alloy thin films

Abstract

The electrocrystallisation of Co, Ni and Co–Ni alloys on ruthenium surface from chloride baths has been studied by cyclic voltammetry and chronoamperometry measurements. The structural and magnetic properties were studied by X-ray diffraction and alternating gradient force magnetometer techniques respectively. The Co–Ni alloys were deposited from solution with molar ratios (Co/Ni) of 5∶1, 1∶1 and 1∶5. From cyclic voltammetry measurements, for all molar ratios for electrodeposited Co–Ni, preferential deposition of Co occurs and anomalous codeposition takes place. Therefore, variation in the composition of thin films alloy is possible depending on the deposition potential. The Scharifker and Hills model was employed to analyse the current transients. For both Co and Co–Ni alloys, the nucleation was a good agreement with the instantaneous model followed by three-dimensional diffusion limited growth. However, for Ni after tmax, the nucleation process changes from progressive to instantaneous model. It is evident that the compositions of the electrolyte do not have influence on the type of nucleation for Co–Ni alloys. X-ray diffraction measurements indicate a small crystallite size with the presence of a mixture of hcp and fcc Co–Ni structures. The hysteresis loops with a magnetic field in the parallel and perpendicular directions showed that the easy magnetisation axis of Co–Ni thin film is in the film plane.