Lightweight macroporous Co-Pt electrodeposited films with semi-hard-magnetic properties

Abstract

Macroporous, partially L10-ordered Co-Pt films with nearly equiatomic composition were successfully synthesized by electrodeposition from an aqueous sulfate–chloride electrolyte on colloidal crystal-templated substrates, followed by annealing in vacuum. The colloids deposited on the substrate consisted of amidine-functionalized polystyrene spheres of 215 ± 13 nm in diameter, which were self-assembled by electrophoresis. As-deposited Co-Pt films obtained after the removal of the spheres showed a highly-packed arrangement of macropores. Structurally, the films showed the A1-disordered face-centered cubic (fcc) Co-Pt solid solution, accompanied by small amounts of fcc/hexagonal close-packed (hcp)–Co. Upon annealing at 600 °C, the A1-disordered phase partly transformed into the L10-ordered (face-centered tetragonal, fct) phase. As a result, the coercivity significantly increased from 148 Oe to 1328 Oe. Importantly, the porosity of the films was preserved after annealing. Optimum annealing temperature and time were selected on the basis of a prior parametric study with electroplated dense counterparts. This work demonstrates that the combination of colloidal crystal templating and electrodeposition is a very convenient pathway towards lightweight semi-hard magnets with potential technological applications in automotive and aerospace industries, portable sensors or spectrometers, magnetic levitation systems, or magnetoelectric devices, among others.