Strain engineering of intrinsic multiferroic coupling in bilayer ScI2

Two-dimensional (2D) sliding ferroelectrics have emerged as promising candidates for next-generation nonvolatile memory technologies. However, integrating magnetic, ferroelectric, and ferrovalley properties within a single material system remains a significant challenge. Here, we propose a strategy combining interlayer sliding and strain engineering to synergistically control magnetism, ferroelectric polarization, magnetic anisotropy energy (MAE), and valley polarization in bilayer ScI2 through first-principles calculations. By altering the stacking order from AA to AB/BA configurations, the magnetic ground state transitions from antiferromagnetic (AFM) to ferromagnetic (FM) ordering, accompanied by the modulation of ferroelectric polarization and valley splitting. External strain further enables precise tuning of these properties: A compressive strain of −2% induces an AFM–FM transition in AB stacked ScI2, while a −6% strain enhances MAE beyond 1 meV. Notably, a tensile strain of 5.71% triggers a semiconductor-to-semimetal transition, transforming the ferrovalley state into a half-valley metal. These findings establish bilayer ScI2 as a versatile platform for the multifunctional device design, offering promising pathways to integrate charge, spin, and valley degrees of freedom in 2D multiferroics.