N2 purging effect on electrodeposition of active ferromagnetic thin FeCo films

Abstract

Electrodeposition of a thin ferromagnetic film with excellent magnetic dynamic properties at gigahertz range is challenging due to the easy oxidation of the active metals. Hence developing a feasible method to decrease the oxidation upon understanding the oxidation mechanism during the electrodeposition is critical. Here we report a simple methodology to successfully electrodeposit thin magnetic soft FeCo films with large complex permeability and high resonant frequency by means of inert gas-purging in the plating solution. The study of mechanism on the electrodeposition of active FeCo films depicts that the purging of inert N2 largely reduces the oxygen content in the plating solution, which subsequently suppresses the oxidation of iron ions, increases the Fe-atom ratio, and also perturbs the crystal growth of the as-deposited FeCo film. This in turn leads to the thin film with significantly reduced oxygen content, smaller grain size, and lower crystallinity, hence increased magnetic moment, decreased coercivity, and notably improved complex permeability of thin FeCo film. Typically, the films have a coercivity as low as 8 Oe, large saturation flux density up to 2.38 T, and ultra-high permeability up to ∼1200 (real part). As such, these thin films have the advantage in the applications for high frequency gigahertz devices.