Magnetically soft and electrically resistive CoNiFeS alloy films prepared by electrodeposition

Magnetic properties of electrodeposited CoNiFeS films were studied to seek their feasibility for applications in microelectromagnetic devices such as high areal density recording heads. We started with NiFe and then expanded experiments to a CoNiFe system. Finally, we added a fourth element, sulfur, to further improve physical properties. A small amount of sulfur inclusion has induced grain size refinement and offered magnetic softness to the film accompanying with increased electrical resistivity. Grain size was found to be in the order of 10 nm. Co₇₃Ni₁₇Fe₉S₁ (in wt. %) films with thickness of 2.5 μm exhibit superior properties compared with currently utilized Ni₄₅Fe₅₅: high saturation magnetic flux density (B_s∼17 kG), low coercivity (H_c∼0.4 Oe), near zero saturation magnetostriction (λ_s∼1.0×10^-6), high permeability (μ∼1300 at 100 MHz), and high electrical resistivity (ρ∼55 μΩ cm). From a processing standpoint, we were able to control film thickness uniformity by adjusting current distributions between the auxiliary electrode and cathode across 100 mm wafers.