A CoFe binary alloy film with 24 kG of saturation magnetic flux density, B s , was prepared by electrodeposition. The B s value of the CoFe alloy film prepared by electrodeposition from the conventional bath is usually equal to 21 kG. With the addition of trimethylamineborane, a well-known reducing agent, the B s value was found to increase to 23 kG. Furthermore, with the use of a separated compartment dual cell system, a B s value as high as 24 kG was reached. For obtaining the highest B s , it was found to be essential to avoid the oxidation of ferrous ion to ferric ion in the plating bath. The coercivity, H c , values were 15, 14, and 15 Oe for the films with 20, 23, and 24 kG of B s , respectively. The key for obtaining high B s materials is to avoid the oxidation of ferrous ions in the bath. In addition, it was found that the H c value of 15 Oe for CoFe film with the highest B s value of 24 kG could be lowered to 8 Oe by annealing in an applied magnetic field of 500 Oe.To meet the strong demand for high performance write-heads to be used for high density magnetic recording, 1 soft magnetic materials with high saturation magnetic density, B s , are being developed by many researchers. 2-6 We previously developed a CoNiFe alloy with B s ϭ 20-21 kG using electrodeposition 7,8 and it has been in practical use. The CoFe binary alloy is known as a material with B s of about 24 kG, which is close to the limiting value achievable with ferromagnetic alloys. 9 Several soft magnetic thin films with the highest B s value of 24 kG have recently been prepared by using a dry sputtering process, e.g., NiFe/CoFe-N/NiFe trilayer film, 10-12 CoFe-O granular film, 13 and CoFe-Al-O granular film. 14,15 However, thin films containing only Co and Fe do not exhibit soft magnetic properties. 16 On the other hand, the technique of electrodeposition is useful as an industrial process, and write-head cores are now being fabricated by electrodeposition. Thus, electrodeposited soft magnetic thin films of CoFe binary alloy with the highest B s value of 24 kG are now in strong demand.We have succeeded in preparing soft magnetic materials of CoFe binary alloy film with B s ϭ 24 kG by electrodeposition. 17 The key requirement for obtaining the high B s CoFe material in this binary alloy system is the prevention of oxidation of ferrous ion, Fe 2ϩ , to ferric ion, Fe 3ϩ , in the plating bath. In this paper, we discuss this key issue in fabricating the soft magnetic material with B s ϭ 24 kG.
ExperimentalBinary CoFe alloy films were electrodeposited using a rotating disk electrode ͑RDE͒ system, in which the anode was made for Pt and the electrodeposited substrate was removable to determine properties of the electrodeposited film. The thickness of the electrodeposited alloy films was about 0.7 m. The substrate was a circular glass plate with a diam of 10 mm, coated with sputtered NiCr ͑5 nm͒ and NiFe ͑100 nm͒ films, and a Cu foil with a diam of 10 mm and a thickness of 8 m. The plating bath composition and operating conditions are shown in Table...
