The continuous and rapid increase of areal density in magnetic data storage systems required a continuous increase of the coercivity of the storage media. In order to be able to record on these everhigher-coercivity media, new soft magnetic materials for pole tips with increased magnetic moment had to be developed. Significant progress has been made during the last few years in electroplating alloys with high saturation magnetic flux density for use in writing heads. We review recent progress made in this area, with particular emphasis on the work done at IBM since the review paper on the subject was published in this journal in 1998 by Andricacos and Robertson. Reviewed here are the high-moment alloys of NiFe, particularly in the very high iron range [an extension of permalloy (Ni 80 Fe 20) and Ni 45 Fe 55 ]; very-high-cobalt CoFeCu alloys; ternary CoNiFe; and binary iron-rich CoFe alloys. With the latter binary alloy films, we have demonstrated that it is possible to reach by electroplating the saturation flux density limit of 2.4-2.5 T reported for cast alloys. Since the electroplating of good-magneticquality iron-rich CoFe alloys posed a considerable challenge, the behavior of the CoFe plating system was studied in detail, using in situ surface pH measurements and a rotating-cylinder Hull cell.

Studies were carried out on the laminated structures FeCo/Cu and FeCo/Ru prepared by two-bath plating, one-bath plating and plating-sputtering hybrid method. Zero remnant magnetization as in antiferromagnetically coupled structures made by sputtering was not achieved. A slow magnetization was observed for structures plated from two baths. A hypothesized mechanism was proposed, involving a superparamagnetic component due to the displacement and corrosion reactions. This effect is less prominent in the structures prepared with one bath plating. Lower magnetic moments were observed, probably due to the inclusion of Cu in FeCo layers as well as a displacement reaction. All the structures prepared by plating-sputtering method behave like a bulk ferromagnetic material. An increase and decrease of the magnetic moment was observed for FeCo/Cu and FeCo/Ru, respectively, probably due to the different effect on the corrosion reaction by Cu and Ru.

The electrodeposition of FeCoRu alloys was studied with rotating disk electrode, surface pH measurements and galvanotstatic plating in a paddle cell. The Ru deposition does not occur until a potential of -0.9 V versus MSE is reached, much higher than the literature reversible potential. In the FeCoRu system, the presence of Ru inhibits the Fe plating rate but exerts no effect on the Co. Surface pH measurements further confirmed the high potential for Ru deposition and a significant hydrogen evolution reaction was observed causing enhanced local agitation at the electrode surface. The effect of complexing agent was also studied for FeCoRu plating. The presence of citrate, tartrate or histidine, were all found to decrease the current efficiency at the conditions of study. While the decrease observed in the citrate and tartrate cases was probably due to the buffering effect, which increases the hydrogen evolution current, histidine was believed to complex with metal cations and to inhibit the metal deposition.

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