On the prospects of magnetic-field-assisted electrodeposition of nano-structured ferromagnetic layers

Micro- and nano-structured ferromagnetic layers are attractive for super-hydrophobic and electrocatalytic applications and can be effectively synthesized using electrodeposition. Beside the use of capping agents, magnetic fields have recently been proven to promote the growth of mm-sized conical structures by alternatively generating a supportive local flow. Here we explore the prospects of using magnetic fields to support the growth of smaller, micro-/nano-sized conical structures. We first elaborate by numerical simulations how the local electrolyte flow and the related inhomogeneous mass transfer change with shrinking cone size. Related scaling laws are derived, and stronger viscous friction along with smaller concentration changes inside the diffusion layer are found to limit the support of the magnetic field. To enhance the structuring effect, pulsed electrodeposition and use of superconducting magnets are discussed. Second, systematic experiments on the template-free electrodeposition of nickel layers in magnetic fields of different orientations and intensities are performed. Regardless of the direction, strong fields are found to promote blunt-ended, shell-like structures. These results are finally discussed by the help of numerical simulations which additionally consider the global cell flow forced by the magnetic fields. Importantly, global flow is found to dominate compared to local flow. We therefore propose improved electrode geometries for future research to clarify the prospects of stronger magnetic fields.