Corrosion properties of electroplated CoNiFe films

Electroplated CoNiFe films with a saturation flux density as high as 2.1 T are potentially useful in high-density magnetic recording heads. We found that films electroplated at a high current density (15 mA/cm²) from a bath without saccharin have a sufficient anodic pitting-corrosion potential (-65 mV). We also found that the pitting-corrosion potential of films electroplated under a low current density (5 mA/cm²) from saccharin-free baths have anodic pitting-corrosion potentials of less than -300 mV. However, the corrosion resistance improved after annealing at temperatures above 100°C. The crystal-grain boundaries in the as-plated film that electroplated under a low current density from saccharin-free baths are not clear (i.e., that the phase is amorphous). But the crystal grain boundaries in the annealed film are clear. Films electroplated from baths containing saccharin also have anodic pitting-corrosion potentials of less than -300 mV. Their corrosion resistance did not improve when they were annealed at 250°C. The deterioration of the corrosion resistance is attributed to the defects that increase the face-centered cubic (111) lattice constant. One of the most important characteristics of a highly corrosion-resistant CoNiFe film is fine crystal structure with very few defects.