Electrodeposition of rare earth-transition metal alloy thin films and nanostructures

Abstract

Rare earth-transition metal alloys are of interest in MEMS and magnetic storage industries because of their unique magnetic properties. However, the applications of these alloys have been limited to bulk and thin film architectures because of the limitations of the contemporary vapor deposition technique to fabricate high aspect ratio nanostructures. The objective of this study is to develop an electrochemical process to deposit rare earth-transition metal alloys thus making it possible to deposit high aspect ratio nanostructures such as nanowires and nanotubes, which helps to tune their properties for specific applications. Electrodeposition of rare earth-transition metal alloys was achieved from an aqueous electrolyte kept under quiescent condition. The effect of cobalt (II) concentration, pH and deposition potential on rare earth-cobalt alloy electrodeposition was investigated. The alloy composition and the partial current densities exhibited a coupled deposition behavior between cobalt and rare earth. The rare earth concentration in the deposit and the current efficiency was found to depend on cobalt (II) concentration. Template electrodeposition of rare earth-transition metal alloy nanowires and nanotubes was demonstrated for the first time. Template deposition enabled the growth of several micron long deposits as compared to about 200 nm thick films deposited on planar substrate. Electrodeposition of rare earth-cobalt alloy nanotubes was observed from unmodified templates under low electrolyte pH, short deposition time and larger pore sizes. Also the composition of the deposit showed strong dependence to diffusion. The crystalline and magnetic properties investigation showed an amorphous deposit with small coercivity and squareness ratio. Compositionally modulated, electrodeposited, multilayered nanowires of CoGd/Co were also demonstrated. Based on the experimental results of rare earth-cobalt alloy deposition on planar electrodes and templates, an electrochemical reaction mechanism and a steady state kinetic model were presented. The mechanism showed a coupled behavior based on competitive adsorption of the intermediates. The kinetic model showed a good data fit between the experimental and simulated results.