Voltage-controlled ON-OFF ferromagnetism at room temperature in a single metal oxide film

Electric-field controlled magnetism can boost energy-efficiency in widespread applications. However, technologically, this effect is facing important challenges: mechanical failure in strain-mediated piezoelectric/magnetostrictive devices, dearth of room-temperature multiferroics or stringent thickness limitations in electrically-charged metallic films. Voltage driven ion motion (magneto-ionics) circumvents most of these drawbacks while offering unprecedented magnetoelectric phenomena. Nevertheless, magneto-ionics typically requires heat-treatments and multi-component heterostructures. Here we report on the electrolytegated and defect-mediated O and Co transport in a Co3O4 single layer which allows for roomtemperature voltage-controlled ON-OFF ferromagnetism (magnetic switch) via internal reduction/oxidation processes. Negative voltages partially reduce Co3O4 to Co (ferromagnetism: ON), resulting in graded films including Co- and O-rich areas. Positive bias oxidizes Co back to Co3O4 (paramagnetism: OFF). This electric-field-induced atomic-scale reconfiguration process is compositionally, structurally and magnetically reversible and self sustained since no oxygen source other than the Co3O4 itself is required. This novel process could lead to new electric-field-controlled device concepts for spintronics