With increasing storage density of hard-disk-drives, the need for recording heads to write on high-coercivity media has raised new requirements for the write-head core material that cannot be met by traditionally employed permalloy (Ni80Fe20). Therefore, new soft magnetic materials with higher saturation flux density Bs (>>1 Tesla) such as CoFe alloys, CoFeNi alloys, and other CoFe-based alloys have been developed during the past decades. With the advantages of simplicity, cost-effectiveness and controllable patterning, electroplating processes are being employed in the fabrication of thin-film recording heads. Conventional CoFe or CoFeNi alloy plating baths, which employ low pH levels (typically 2.0-3.0), suffer from several problems that can limit commercialization. These include poor stability, i.e., precipitation occurs in plating baths rapidly with time, low current density efficiency and voids in deposited films due to the electrodeposition of hydrogen. The voids present in deposits will degenerate film uniformity and magnetic properties. Therefore, the development of stable baths with relatively high pH levels is crucial for commercial fabrication of CoFe and CoFeNi thin films with optimal soft magnetic properties.

In this study, stable electrolytes, with the introduction of ammonium citrate as a complexing agent and bath stabilizer and relatively high pH levels (natural pH), have been developed for the electrodeposition of CoFe or CoFeNi alloys. Citrate can effectively improve the stability of CoFe and CoFeNi plating baths. Denser and more uniform deposits can be plated out from the citrate-added baths because of the higher pH levels. CoFe and CoFeNi thin films with preferred composition, mixed fcc-bcc phases, and 10-20nm grain sizes, which are necessary for achieving optimal soft magnetic properties, have been electroplated from the citrate-added baths. So far, the saturation magnetizations of CoFe and CoFeNi films plated from citrate-added baths can exceed 2 Tesla, which is excellent, and the coercivities of the CoFe and CoFeNi films are acceptable (9 to 17 Oe). The stability diagrams of single metal and alloy plating baths, with and without citrate addition, have been calculated. Electrochemical study of the electrodeposition of Co, Fe and Ni single metals and CoFe and CoFeNi alloys, from citrate-added baths and citrate-free baths, and the corrosion properties of electroplated CoFe and CoFeNi films have been conducted. The phase formation and grain sizes in electrodeposited CoFe and CoFeNi films have been investigated using thin film x-ray diffraction (XRD) and transmission electron microscopy (TEM) methods.