Intrinsic Half‐Metallicity in 2D Ternary Chalcogenides with High Critical Temperature and Controllable Magnetization Direction

Abstract Searching for 2D ferromagnetic materials with a high critical temperature, large spin polarization, and controllable magnetization direction is a key challenge for their broad applications in spintronics. Here, through a systematic study on a series of 2D ternary chalcogenides with first‐principles calculations, it is demonstrated that a family of experimentally available 2D CoGa 2 X 4 (X = S, Se, or Te) are half‐metallic ferromagnets, and they exhibit high critical temperature, fully polarized spin state, and strain‐dependent magnetization direction simultaneously. Following the Goodenough–Kanamori rules, the half‐metallic ferromagnetism of CoGa 2 X 4 family is caused by superexchange interaction mediated by CoXCo bonds. The half‐metal gaps are large enough (>0.5 eV) to ensure that the half‐metallicity is stable against the spin flipping at room temperature. Magnetocrystalline anisotropy energy calculations indicate that CoGa 2 X 4 favor easy plane magnetization. Under achievable biaxial tensile strain (2–6%), the magnetization directions of CoGa 2 X 4 can change from in‐plane to out‐of‐plane, providing a route to control the efficiency of spin injection/detection. Further, the critical temperatures T c of ferromagnetic phase transition for CoGa 2 X 4 are close to room temperature. Belonging to the big family of layered AB 2 X 4 compounds, the proposed CoGa 2 X 4 systems will enrich the available 2D candidates and their heterojunctions for various applications.