Half-Metallic 2D ScSi₂N₄ Phases with Non-Metal-Induced Ferromagnetism and Tunable Electronic and Optical Properties

Two-dimensional (2D) intrinsic half-metal materials facilitate spin filtering, low-energy dissipation, and enhanced signal integrity, making them highly desirable for next-generation nanoelectronics and quantum technologies. In this work, we constructed two novel 2D half-metallic materials, α₁-ScSi₂N₄, and α₂-ScSi₂N₄, with unconventional ferromagnetism originating from N atoms rather than the transition metal Sc. First-principles calculations confirm their dynamic and thermal stability, as well as their intrinsic half-metallicity. We further demonstrate that their electronic and optical properties can be effectively tuned via strain, atomic adsorption, and external electric fields. A half-metal-to-metal transition occurs under compressive strain (α₁: 10%; α₂: 6-10%), while H/F adsorption induces a metallic state in α₁, and H adsorption does so in α₂. Furthermore, α₁ becomes metallic at electric fields of -0.2 to -0.5 V/Å and 0.2 to 0.5 V/Å, while α₂ undergoes a similar transition at electric fields of -0.3 to -0.5 V/Å and 0.3 to 0.5 V/Å. Both materials exhibit strong deep-UV absorption, indicating potential in optoelectronics. Symmetry breaking, charge transfer and energy level shifting maybe the tunability mechanisms caused the half-metal-to-metal transition. These findings not only expand the family of 2D half-metals with non-metal-derived magnetism but also provide new avenues for designing tunable magnetic materials for reconfigurable electronic, spintronic, and photonic applications.