| Alloyed nickel-iron with the composition of 80:20 weight percent nickel-to-iron ratio is referred to as permalloy. Thin films of permalloy, on the order of microns, are used in the magnetic recording industry for recording heads or as a backlayer for Co-Cr perpendicular recording. An important requirement of these films is reproducible magnetic properties, which requires stringent control of processing variables. Typical permalloy plating baths contain 40 times as much nickel as iron in order to accommodate anomalous codeposition, in which the less noble metal, Fe, deposits preferentially to the more noble metal, Ni. The goal of this research is to investigate the electrodeposition of NiFe in order to understand the mechanism, in general, and its sensitivity to processing conditions.;The experimental approach is to investigate the deposition mechanism by deposit analysis and potentiostatic cathodic polarization. The process variables under investigation are bath composition, bath agitation, and applied potential. The plating solution contained nickel and iron sulfate salts of varying concentrations and boric acid, when required. The results suggest that the dissolved oxygen concentration in the bath is a significant process variable for solutions which include boric acid.;The approach to model the anomalous codeposition of nickel-iron is comprised of two parts; equilibrium calculations and one-dimensional diffusion modeling. The equilibrium formation of hydroxide species as a function of pH showed that at equilibrium, the relative concentration of the MOH+ species follows the order of preferred electrodeposition for nickel and iron, as well as cobalt and zinc; species which all exhibit anomalous codeposition. The initial one-dimensional diffusion model examined hydrogen evolution during deposition. The results of this model, in addition to the equilibrium calculations suggest a reaction scheme which assumes NiOH+ and FeOH+ as the species which undergo charge transfer at the cathode. Thus, a second model is used to predict the nickel-to-iron ratio of the deposits and the surface concentrations of significant species using the experimental results. The model was extended to include boric acid, a nickelous-borate complex, and a ferric-borate complex. Experimental results and model predictions agree for plating solutions without boric acid. |
