Influence of Debubbling on Crystal Structure and Magnetic Properties of Electrodeposited CoNiP Layers

Abstract

Various stirring methods, including a magnetic stirrer, nitrogen bubbling, and ultrasonic stirring, were investigated to debubbling hydrogen during electrodeposition of $25~\mu \text{m}$ -thick Co76Ni18P6 layers on copper. Microstructure observation shows that a lot of hillocks form on the surface of Co–Ni–P films when using magnetic stirring. While a smooth surface morphology was obtained for those using nitrogen bubbling and ultrasonic stirring. This manifests effective depriving of hydrogen during electrodeposition with the later two stirring methods. All Co–Ni–P layers exhibit the coexistence of hexagonal closed packing (HCP) and face-centered cubic phases. The films obtained using magnetic stirring have a random crystalline orientation and longitudinal magnetic anisotropy showing intrinsic coercivity ( $H_{\mathrm {ci}}$ ) 1.45 kOe and remanence ( $M_{r}$ ) 7.7 kG. Nitrogen bubbling bestows Co–Ni–P layers a rather strong HCP (002) texture, which leads to the enhanced perpendicular magnetic anisotropy showing out-of-plane $H_{\mathrm {ci}}~2.65$ kOe and $M_{r}$ 1.9 kG. On the other hand, samples deposited using ultrasonic stirring have a relatively weak HCP (002) texture, and thus the magnetic behavior is longitudinal. Ultrasound vibration induces local heating and cavitation on the electroplating surface leading to the deteriorated (002) texture and surface roughening than that of the nitrogen bubbling.