Large magnetoelectric effects in electrodeposited nanoporous micro-disks driven by effective surface charging and magneto-ionics.

A synergetic approach to enhance magnetoelectric effects (i.e., control of magnetism with voltage) and improve energy efficiency in magnetically actuated devices is presented. The investigated material consists of an ordered array of Co-Pt micro-disks, in which nanoporosity and partial oxidation are introduced during the synthetic procedure to synergetically boost the effects of electric field. The micro-disks are grown by electrodeposition from an electrolyte containing an amphiphilic polymeric surfactant. The bath formulation is designed to favor the incorporation of oxygen in the form of cobalt oxide. A pronounced reduction of coercivity (88%) and a remarkable increase of Kerr signal amplitude (60%) are observed at room temperature upon subjecting the micro-disks to negative voltages through an electrical double layer. These large voltage-induced changes in the magnetic properties of the micro-disks are due to: (i) the high surface area-to-volume ratio with ultra-narrow pore walls (sub-10 nm) that promote enhanced electric charge accumulation and (ii) magneto-ionic effects, where voltage-driven O migration promotes a partial reduction of CoO to Co at room temperature. This simple and versatile procedure to fabricate patterned 'nano-in-micro' magnetic motifs with adjustable voltage-driven magnetic properties is very appealing for energy-efficient magnetic recording systems and other magnetoelectronic devices.