Electroplating of Nanocrystalline CoFeNi Soft Magnetic Thin Films from a Stable Citrate-Based Bath

Abstract

CoFeNi alloys are some of the most studied soft magnetic materials because of their superior properties over FeNi alloys as write head core materials in hard-disk-drives. Electroplating processes have major significance in the fabrication of thin-film recording heads due to their advantages of simplicity, cost-effectiveness, and controllable patterning. Conventional low pH (2.5-3.0) baths suffer from problems such as poor stability, low current density efficiency, and voids in deposited films due to the electroplating of hydrogen. A new, stable citrate-based bath has been developed in this study. Citrate can effectively improve the stability of CoFeNi plating baths, and denser CoFeNi films can be plated out because of the higher bath pH (>5). The effects of bath composition and plating conditions on the electroplating of CoFeNi thin films have been studied. CoFeNi thin films with preferred composition, mixed fcc-bcc phases, and 10-20 nm grain sizes have been plated out from the new citrate-based bath.

Effect of Ammonium Chloride in Plating Baths on Soft Magnetic Properties of Electroplated Fe–Ni Films

“…In our previous study for the citric acid, both the current efficiency and the Fe content decreases with increasing the concentration of the citric acid [5]. In contrast, both the current efficiency and the Fe content show almost constant values except for 0 g/L of NH4Cl, indicating that we can vary the concentration of NH 4 Cl without the change in the Fe content. The current efficiency of approximately 95% is much higher than those for our previous study (85%) [5] and other researcher's ones (60 -80%) [10][11].…”

“…Osaka et al have been reported Co-Fe-Ni films with high saturation magnetic flux density and low coercivity using ammonium chloride (NH4Cl) [8]. For electroplating of Ni films, the effect of NH 4 Cl on the crystal orientation has been reported [9]. As the orientation is one of factors to determine magnetic properties, we expected an improvement in soft magnetic properties of electroplated FeNi films.…”

“…All measurements were carried out for the Fe-Ni films in an as-plated state. Figure 1 shows Fe content and current efficiency as a function of NH 4 Cl concentration. The concentrations of FeSO 4 and NaCl were fixed at 53 and 50 g/L, respectively.…”

“…Figure 1 shows Fe content and current efficiency as a function of NH 4 Cl concentration. The concentrations of FeSO 4 and NaCl were fixed at 53 and 50 g/L, respectively. In our previous study for the citric acid, both the current efficiency and the Fe content decreases with increasing the concentration of the citric acid [5].…”

“…Thus, a complexing agent is typically used for electroplating of Fe-group films. For the plating of Fe-group films, citrates are one of hopeful complexing agents [4][5], and chloride media are also often employed [6][7]. Osaka et al have been reported Co-Fe-Ni films with high saturation magnetic flux density and low coercivity using ammonium chloride (NH4Cl) [8].…”