Preparation of high magnetic flux density CoNiFeB film by electroless deposition for application to magnetic recording devices

A CoNiFeB soft magnetic thin film with high saturation magnetic flux density (B_s) for use as a magnetic recording head core material or as a soft magnetic underlayer of a double perpendicular magnetic recording medium was prepared by electroless deposition. When the CoNiFeB alloy thin film was deposited on a evaporated Cu (100 nm thick)/glass substrate, the saturated magnetic flux density was found to increase up to 2.0 T by increasing the concentration of FeSO₄. The coercivity (H_c) was found to decrease to 6 Oe while the saturated magnetic flux density was maintained higher than 1.8 T by optimizing the concentrations of tartaric acid and citric acid in the electroless plating solution. An X-ray diffraction (XRD) study showed that the intensity of the assigned peak in the bcc (1 1 0) of CoNiFeB film decreased as the concentration of tartaric acid was decreased. Moreover, the coercivity of the CoNiFeB film formed on a NiFe substrate exhibits lower coercivity than that formed on a Cu substrate.