Electrodeposited NiFeCo + Tb and Dy for enhanced magnetostrictive properties and soft magnetism

Abstract

Magnetostrictive thin films have numerous applications in communications, sensors, and microelectronic devices. Such devices usually require magnetostrictive thin films with large magnetostriction and soft magnetic properties. Nickel-Iron-Cobalt (NiFeCo) alloys have excellent soft magnetic properties and can be easily fabricated as thin films. However, their main drawback for these sensing applications is that they have very low magnetostriction. On the other hand, Iron-Rare Earth (RE) alloys such as Fe-Tb-Dy or Fe-Ga have large magnetostriction at the cost of some soft magnetic properties. Moreover, their magnetostrictive properties are degraded when reduced to thin films as opposed to bulk materials due to structural imperfections and oxidation of the REs. In this paper, we report the development of NiFeCo thin films with incorporated rare earth elements prepared via electrodeposition. Electrochemical cells were prepared using Ni, Fe, and Co sulfate salts. Tb and Dy sulfates were added to the electrochemical cell in order of increasing concentration. Electrodeposition was then carried out under galvanostatic control for each RE concentration in the bath. The produced films were analyzed for composition, crystallinity, and magnetic properties to draw out trends based on the initial concentrations of rare earth salts in the bath. The produced thin films retained soft magnetic properties while exhibiting giant magnetostriction of up to ∼370 ppm depending on the type and amount of incorporated REs within the film. The combination of soft magnetism and giant magnetostriction makes these NiFeCo thin films with added Tb and Dy excellent candidates for developing resonant frequency sensing devices.