Tunable Magnetism in 2D XI₂ (X = Fe, Co, Ni) Monolayers: The Potential Toward Room-Temperature Functional Spintronic Materials

Abstract Two-dimensional (2D) materials with room-temperature magnetism and large magnetic anisotropy energy (MAE) are essential for advancing next-generation nanoscale spintronic devices. In this work, we systematically investigate the structural, magnetic, and electronic properties of XI2 (X = Fe, Co, Ni) monolayers based on first-principles calculations. In all three materials, the transition metal atoms occupy the centers of hexagonal rings and are coordinated by iodine atoms in a hexagonal geometry. Among them, CoI2 exhibits a Curie temperature as high as 320 K, indicating promising room-temperature ferromagnetism. All three monolayers exhibit relatively large MAE values, with NiI2 showing the largest, primarily due to strong spin-orbit coupling and pronounced orbital hybridization between Ni-3d and I-5p orbitals. The easy magnetization axis lies in-plane for FeI2 and CoI2, and out-of-plane for NiI2. Under biaxial strains ranging from −3% to +3%, FeI2 and NiI2 retain their antiferromagnetic (AFM) and ferromagnetic (FM) ground states, respectively, demonstrating robust magnetic phase stability. In contrast, CoI2 undergoes a strain-induced transition between FM and AFM states, offering a pathway to strain-tunable magnetism. Furthermore, ab initio molecular dynamics(AIMD) simulations confirm the thermodynamic stability of FeI2 up to 1000 K. These combined features—high Curie temperature, large MAE, and excellent thermal and magnetic robustness—highlight XI2 monolayers as promising candidates for future nanoscale spintronic applications.