A nonvolatile multistate memory by electric field control of half-metallicity in a noncentrosymmetric FeI2 bilayer coupled with ferroelectric α -In2Se3

The development of high-density, low-power spintronic memory demands nonvolatile control of spin-dependent transport properties. Here, we demonstrate electric field-induced reversible half-metallic transitions in a van der Waals heterostructure comprising a twisted ferromagnetic FeI2 bilayer (bi-FeI2) and ferroelectric α-In2Se3. Breaking inversion symmetry via a 180° interlayer twist in bi-FeI2 stabilizes ferromagnetic order, while coupling with α-In2Se3 enables polarization-dependent band topology modulation. First-principles calculations reveal that switching α-In2Se3 polarization triggers a semiconductor-to-half-metal transition in bi-FeI2, driven by interfacial charge redistribution and spin-polarized band shifts near the Fermi level. The heterostructure further exhibits electrically tunable four resistance states, suggesting a route toward ultrahigh-density memory. By integrating interfacial magnetoelectric coupling with structural symmetry engineering, our work provides a paradigm for designing energy-efficient, electrically programmable spintronic devices beyond conventional magnetoresistive architectures.