Enhancing magneto-ionic effects in cobalt oxide films by electrolyte engineering.

Electric-field-driven ion motion to tailor magnetic properties of materials (magneto-ionics) offers much promise in the pursuit of voltage-controlled magnetism for highly energy-efficient spintronic devices. Electrolyte gating is a relevant means to create intense electric fields at the interface between magneto-ionic materials and electrolytes through the so-called electric double layer (EDL). Here, improved magneto-ionic performance is achieved in electrolyte-gated cobalt oxide thin films with the addition of inorganic salts (potassium iodide, potassium chloride, and calcium tetrafluoroborate) to anhydrous propylene carbonate (PC) electrolyte. molecular dynamics simulations of the EDL structure show that K is preferentially located on the cobalt oxide surface and KI (when compared to KCl) favors the accumulation of positive charge close to the surface. It is demonstrated that room temperature magneto-ionics in cobalt oxide thin films is dramatically enhanced in KI-containing PC electrolyte at an optimum concentration, leading to 11-fold increase of generated magnetization and 35-fold increase of magneto-ionic rate compared to bare PC.