High-temperature ferromagnetism in MCr₂X₄ (M = Mg, Zn; X = S, Se) monolayers

Two-dimensional intrinsic ferromagnetic (FM) materials with a Curie temperature (T_C) above room temperature and tunable half-metallic electronic structures are highly desirable for potential spintronic device applications. This work presents a first-principles study of MCr₂X₄ (M = Mg, Zn; X = S, Se) monolayers, which are constructed by intercalating M into 1T-CrS₂ bilayers. Our calculations reveal that MCr₂X₄ monolayers with D_3d symmetry are thermodynamically stable. Intercalation induces a magnetic ground state transition from the antiferromagnetic (AFM) state of pristine 1T-CrS₂ to a robust FM state in MCr₂X₄ monolayers, with a T_C exceeding room temperature (T_C > 324 K). The easy magnetization axes are found to be in the out-of-plane direction for MCr₂S₄ monolayers and in the in-plane direction for MCr₂Se₄ monolayers. Carrier doping drives the MCr₂X₄ monolayers to undergo a transition from an FM semiconductor to a half-metallic state, featuring 100% spin-polarization in the spin-up channel. Furthermore, electron doping reduces the T_C, whereas hole doping increases it. This study provides a foundation for designing 2D FM materials and enhances our understanding of the magnetic properties of MCr₂X₄ monolayers.