Low voltage induced reversible magnetoelectric coupling in Fe₃O₄ thin films for voltage tunable spintronic devices

The ongoing demand for efficient and low-energy consumption spintronic devices has motivated the idea of manipulating magnetism by ionic liquid (IL) electrolyte gating at low voltages. Although magnetoelectric (ME) coupling has already been realized in some field-effect-transistor (FET) structures, some vital parameters such as giant ME coupling coefficient, excellent reversibility and low gating voltage seldom come at the same time, which greatly suppresses industrialization. Here we demonstrate a large 552 Oe spin dynamics modulation of Fe₃O₄ thin films induced at a gating voltage of V_g = +1.5 V in an IL-gated Au/[DEME]⁺[TFSI]^-/Fe₃O₄/MgO heterostructure with good reversibility up to 80 cycles, giving rise to a high ME coefficient of 368 Oe V^-1. Such a large ME tunability under low V_g could be attributed to the electric field (E-field) induced ionic transformation between Fe²⁺ and Fe³⁺ at the interface. The tiny thickness change (∼2 angstrom) and roughness change of Fe₃O₄ films under V_g = +1.5 V illustrated by in situ X-ray reflection (XRR) give a reasonable explanation of the outstanding reversible property. Interestingly, it is found that the Verwey transition temperature of Fe₃O₄ has a strong dependence on V_g, revealing the potential of IL gating control of the intrinsic spin ordering inside magnetic films. This work drives forward the low-voltage induced reversible ME coupling to high-performance spintronic devices.