Electrochemical preparation of soft magnetic CoNiFeS film with high saturation magnetic flux density and high resistivity

A soft magnetic CoNiFeS film as a write head core material for the next generation was prepared by electrodeposition. In this system, thiourea was used as an additive in the CoNiFe ternary alloy plating bath. The most suitable magnetic properties were obtained at the film composition of (Co₇₃Ni₁₂Fe₁₅)_99.1S_0.9 [atomic percent (a/o)] with a high saturation magnetic flux density (B_s) of 1.7 T, a high resistivity (ρ) of 51 μΩ cm, and a low saturation magnetostriction (λ_s) of 4.4 × 10^-6. The film consisted of fine minute crystal grains 5 to 10 nm in diameter. The S content of ca. 0.9 a/o is believed to be responsible for the formation of small crystal grains with low coercivity and high resistivity.