The Influence of Ammonia on the Electroless Deposition of CoB Alloys from Alkaline Citrate containing Baths

When adjusting the pH of deposition baths, ammonia (NH3) is often used instead of sodium hydroxide (NaOH), but its effects on the chemical and/or electrochemical processes are not usually considered. Here the influence of NH3 on the deposition rate, composition and magnetic properties of amorphous cobalt-boron (CoB) alloys deposited from alkaline plating baths containing citrate is discussed. We have observed that when the pH of the solution was adjusted with NH3, CoB films were deposited at higher rates and the B content decreased with increasing pH. Opposite trends were observed when NaOH was used to adjust the bath pH. These observations were discussed in terms of the complex species distribution in solution and of the buffering characteristics of NH3. The reducing agent, dimethylaminoborane, has its electrooxidation also affected by the presence of NH3 in solution. Amorphous, soft CoB magnetic films with coercivity values varying from 40 Oe to 80 Oe, inversely dependent on the B content of the film, were obtained.