Voltage-induced Ferromagnetism in Diamagnetic FeS2

Abstract

Increasingly impressive demonstrations of voltage-controlled magnetism have been achieved recently, highlighting the potential for low-power data processing and storage devices. Magnetoionic approaches appear particularly promising, electrolyte- and ionic-conductor-based devices being shown capable of on/off voltage control of ferromagnetism and voltage tuning of magnetic anisotropy [1-3]. A clear limitation, however, is that such demonstrations involve either electrically tuning a known ferromagnet, or electrically inducing ferromagnetism from another magnetic state, e.g., antiferromagnetic. In this work, we report 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 [4]. We use ionic-liquid-gated diamagnetic semiconducting FeS2 as a model system, showing that as little as +1 V gate bias induces a highly reversible insulator-metal transition, driven by electrostatic inversion of the surface from a p-type semiconductor to an n-type metal. Anomalous Hall effect measurements then reveal the onset of robust electrically-tunable surface ferromagnetism at Curie temperatures up to 25 K, with intriguing high temperature spin correlations. Density-functional-theory-based modelling explains the induced magnetism in terms of Stoner-type ferromagnetism induced solely via filling of a narrow Fe eg band. Work supported primarily by the NSF MRSEC.