A novel CoCuP electrodeposited film with improved planar hard magnetic properties and film quality

We designed to add Cu into Co-P hard magnetic films prepared via electroplating. The purpose was to make use of immiscibility between Co and Cu, hoping that Cu will segregate at Co-grain-boundaries to mediate magnetic decoupling. Copper is found very difficult to co-electrodeposit with Co due to the large difference in the reduction potentials. A slight variation of CuSO4 concentration in the electrolyte from 1 mM to 2 mM results in a big difference of Cu content from 3.8 wt% to 13 wt% in CoCuP films. However, the CoCuP films are amazingly crack-free up to a thickness no less than 6 μm. The films electroplated with CuSO4 concentration 1.3 mM at pH 4.7 and 25 °C have a Cu content 5.5 wt%, P content 3.1 wt% and exhibit the best magnetic properties. The in-plane magnetic properties are Hc 360 Oe, Br 7450 G, and (BH)m 1.21 MGOe. The perpendicular ones are Hc 800 Oe, Br 1600 G, and (BH)m 0.35 MGOe. The evolution in film composition, microstructure and crystal structure well explains the variation in resultant magnetic properties. These films are readily applicable in mini- and micro-devices which need in-plane magnetic performance. •A crack-free hard magnetic film of CoCuP has been successfully electroplated.•Optimized magnetic properties of CoCuP films were studied through electroplating parameters.•The crack-free CoCuP films results from the residual stress release via the codeposition of Cu in CoP films.