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 XI 2 (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, CoI 2 exhibits a Curie temperature as high as 320 K, indicating promising room-temperature ferromagnetism. All three monolayers exhibit relatively large MAE values, with NiI 2 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 FeI 2 and CoI 2 , and out-of-plane for NiI 2 . Under biaxial strains ranging from −3% to +3%, FeI 2 and NiI 2 retain their antiferromagnetic (AFM) and ferromagnetic (FM) ground states, respectively, demonstrating robust magnetic phase stability. In contrast, CoI 2 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 FeI 2 up to 1000 K. These combined features—high Curie temperature, large MAE, and excellent thermal and magnetic robustness—highlight XI 2 monolayers as promising candidates for future nanoscale spintronic applications.