Enhancing magneto-ionic effects in magnetic nanostructured films via conformal deposition of nanolayers with oxygen getter/donor capabilities.

Effective electric-field manipulation of the magnetic properties of nanostructured metallic alloys exhibiting inter-grain porosity (i.e., channels) conformally coated with insulating oxide nanolayers is demonstrated. Nanostructured Co-Pt films are prepared by electrodeposition (ED) and subsequently coated with either AlOx or HfOx by atomic layer deposition (ALD) to promote magneto-ionic effects (i.e., voltage-driven ion migration) during electrolyte-gating. Pronounced variations in coercivity (HC) and magnetic moment at saturation (mS) are observed at room temperature after biasing the heterostructures. The application of a negative voltage results in a decrease of HC and an increase of mS, whereas the opposite trend is achieved for positive voltages. Although magneto-ionic phenomena are already observed in uncoated Co-Pt films (due to the inherent presence of oxygen), the ALD oxide nanocoatings serve to drastically enhance the magneto-ionic effects due to partially reversible voltage-driven oxygen migration across the interface between AlOx or HfOx and the nanostructured Co-Pt film. Co-Pt/HfOx heterostructures exhibit the most significant magnetoelectric response at negative voltages, with an increase of mS up to 76% and a decrease of HC by 58%. The combination of a nanostructured magnetic alloy and a skin-like insulating oxide nanocoating is shown to be appealing to enhance magneto-ionic effects, potentially enabling electrolyte-gated magneto-ionic technology.