Voltage-Controlled ON–OFF Ferromagnetism at Room Temperature in a Single Metal Oxide Film

Abstract

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 ionic motion (magneto-ionics) circumvents most of these drawbacks while exhibiting interesting magnetoelectric phenomena. Nevertheless, magneto-ionics typically requires heat treatments and multicomponent heterostructures. Here we report on the electrolytegated and defect-mediated O and Co transport in a Co 3 O 4 single layer which allows for room-temperature voltage-controlled ON−OFF ferromagnetism (magnetic switch) via internal reduction/oxidation processes. Negative voltages partially reduce Co 3 O 4 to Co (ferromagnetism: ON), resulting in graded films including Co-and O-rich areas. Positive bias oxidizes Co back to Co 3 O 4 (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 Co 3 O 4 itself is required. This process could lead to electric-field-controlled device concepts for spintronics.

Disentangling Highly Asymmetric Magnetoelectric Effects in Engineered Multiferroic Heterostructures

“…After discarding charge effects, we focus on possible voltage-driven oxygen migration (i.e., magnetoionics) phenomena since this magnetoelectric mechanism is polarity dependent and it could result in strong permanent (nonvolatile) changes [35][36][37][38]40,41]. As can be seen in Fig.…”

“…Moreover, in contrast to piezostrain and direct field effects, magnetoionics results not only in changes of extrinsic magnetic properties, such as coercivity or remanence, but also in saturation magnetization (which can precisely sense the degree of oxidation). In most of these studies, detailed investigations of eventual changes in the saturation magnetization with applied voltage have been largely omitted, thus overlooking possible voltage-driven oxygen diffusion (magnetoionics) phenomena [35][36][37][38][39][40][41], which also depend on the electric polarity. As a clear example, Ref.…”

“…As a clear example, Ref. [40] reports on the voltage-controlled ON-OFF room temperature ferromagnetism in paramagnetic Co 3 O 4 . A negative voltage partly reduces Co 3 O 4 to Co (ferromagnetism: ON), resulting in a graded material including Co-to Orich regions.…”

Voltage‐Control of Magnetism in All‐Solid‐State and Solid/Liquid Magnetoelectric Composites

“…Further, a shift in the onset of magnetoresistance of up to 30 K was induced by O 2− migration in SRO films gated with EMI-TFSA ion gel. [180] So far, investigations on magnetoionics have been focused on the voltage-control of single ionic species. Electrolyte-gated Co 3 O 4 films featuring room-temperature paramagnetism displayed the emergence of a ferromagnetic state due to creation of Co clusters upon diffusion of oxygen ions.…”

Magneto‐Ionic Switching of Superparamagnetism

“…Besides multiferroic materials or diluted magnetic semiconductors, electrochemical setups have recently been investigated for that purpose . One can distinguish three fundamentally different processes at the electrode–electrolyte interface, which can be exploited for the electrochemical control of magnetism: I) capacitive or pseudo‐capacitive double‐layer charging, II) redox surface reactions, or III) bulk intercalation triggered by chemical reactions (magneto‐ionic effect) . As high surface‐to‐volume ratios are beneficial for all three tuning approaches, recent studies have mainly focused on ultra‐thin films and nanoporous materials …”