Structural and magnetic properties of high saturation induction CoNiFe electroplated films

The structure and saturation induction (B_s) of Co_90-xNi₁₀Fe_x (8 ≤ x ≤ 40) electroplated films have been studied with a view to their use as high-density write-core materials. The B_s of the films were slightly larger than those of CoNiFe powders and were increased into the 1.8 to 2.1 T range by controlling the Fe composition and the amount of bcc phase. The latter was achieved by controlling the plating conditions, i.e., the current density and bath temperature. The hyperfine field of the films was about 34 T, slightly larger than that of the powders (33 T), suggesting that their magnetic moments were slightly larger than those of equivalent bulk alloys. The B_s values were increased by increases of the amount of bcc phase relative to the equilibrium phase with increasing the magnetic moments. A band calculation showed that the bcc phase had a larger magnetization than the fcc phase although the difference between the total energies of the two phases was fairly small. This confirmed our results.