Quantitative Determination on Ionic‐Liquid‐Gating Control of Interfacial Magnetism

Ionic‐liquid gating on a functional thin film with a low voltage has drawn a lot of attention due to rich chemical, electronic, and magnetic phenomena at the interface. Here, a key challenge in quantitative determination of voltage‐controlled magnetic anisotropy (VCMA) in Au/[DEME]⁺[TFSI]⁻/Co field‐effect transistor heterostructures is addressed. The magnetic anisotropy change as response to the gating voltage is precisely detected by in situ electron spin resonance measurements. A reversible change of magnetic anisotropy up to 219 Oe is achieved with a low gating voltage of 1.5 V at room temperature, corresponding to a record high VCMA coefficient of ≈146 Oe V⁻¹. Two gating effects, the electrostatic doping and electrochemical reaction, are distinguished at various gating voltage regions, as confirmed by X‐ray photoelectron spectroscopy and atomic force microscopy experiments. This work shows a unique ionic‐liquid‐gating system for strong interfacial magnetoelectric coupling with many practical advantages, paving the way toward ion‐liquid‐gating spintronic/electronic devices.