Voltage-induced ferromagnetism in diamagnetic FeS₂

Increasingly impressive demonstrations of voltage-controlled magnetism have been achieved recently, highlighting potential for low-power data processing and storage. Magnetoionic approaches appear particularly promising, electrolytes and ionic conductors being shown capable of on/off control of ferromagnetism and tuning of magnetic anisotropy. A clear limitation, however, is that such devices either electrically tune a known ferromagnet, or electrically induce ferromagnetism from another magnetic state, e.g., antiferromagnetic. Here, we provide proof-of-principle that ferromagnetism can be voltage-induced even from a diamagnetic, i.e., zero-spin state, suggesting that useful magnetic phases could be electrically-induced in “non-magnetic” materials [1]. We use ionic-liquid-gated diamagnetic FeS₂ as a model system, showing that as little as 1 V induces a reversible insulator-metal transition, driven by electrostatic surface inversion. Anomalous Hall measurements then reveal the onset of electrically-tunable surface ferromagnetism at up to 25 K. Density-functional-theory-based modelling explains this in terms of Stoner ferromagnetism induced via filling of a narrow e_g band.
[1] Walter et al., Science Advances 6, eabb7721 (2020)