2D Multiferroics in As-Substituted Bilayer α-In2Se3 with Enhanced Magnetic Moments for Next-Generation Nonvolatile Memory Device

Searching for multiferroic materials with ferromagnetic (FM) and ferroelectric (FE) properties holds promise for ultra-high-density and low-energy-consumption memory device applications, but 2D materials with both properties are rare. Herein, a general strategy to achieve nonvolatile electric field control of magnetism in the bilayer (BL) alpha-In2Se3 by hole doping is proposed. By first-principles calculations, it is demonstrated that hole doping can induce robust ferromagnetism in the bilayer alpha-In2Se3 due to its unique flat Mexican-hat-shape valence band structure. Such band edges cause van Hove singularities (VHS), and proper hole doping can lead to time-reversal symmetry breaking. The bilayer alpha-In2Se3 exhibits ferromagnetism and ferroelectricity within a wide range of doping concentrations, resulting in an unexpected multiferroic phase. Furthermore, when the electrical polarization of alpha-In2Se3 flips from downward to upward, it becomes non-magnetic (NM) from ferromagnetic states in the As-substituted bilayer alpha-In2Se3, which can work as a nonvolatile magnetic storage unit. Remarkably, the As-substituted bilayer alpha-In2Se3 exhibits an enhanced magnetic moment of 1.2 mu(B) per As-Se due to substantial charge transfer across the interface. Notably, the mechanism of electrically controlled magnetism is elucidated as the coupling among the Mexican-hat-like dispersion, ferromagnetism, and ferroelectricity. The findings offer a promising strategy for electrical writing and the magnetic reading memory device.