Dirac semimetallic Janus Ni-trihalide monolayer with strain-tunable magnetic anisotropy and electronic properties†

Two-dimensional (2D) ferromagnetic (FM) semiconductors have been paid much attention due to the potential applications in spintronics. Here, the electronic and magnetic properties of 2D Janus Ni-trihalide monolayer Ni₂X₃Y₃ (X, Y = I, Br, Cl; X ≠ Y) are investigated by first-principle calculations. The properties of Ni₂X₃Y₃ (X, Y = I, Br, Cl; X ≠ Y) monolayers are compared by selecting the NiCl₃ monolayer as the reference material. Ni₂X₃Y₃ monolayers have two distinct magnetic ground states of ferromagnetic (FM) and antiferromagnetic (AFM). In the Ni₂X₃Y₃ monolayer, two different orbital splits were observed, one semiconductor state and the other semimetal state. The semimetal state of Ni₂X₃Y₃ can be tuned to semiconductor or metallic state when biaxial strain is applied. The magnetic anisotropy energy (MAE) of the Ni₂X₃Y₃ monolayer can display variations compared to that of the NiCl₃ monolayer, with the direction of easy magnetization being influenced by the specific halogen elements present. The easy magnetization direction of Ni₂X₃Y₃ can also be changed by applying biaxial strain. The T_c of Ni₂X₃Y₃ is predicted to be about 100 K according to the calculation of the E_AFM–E_FM model. The design of the Janus Ni₂X₃Y₃ structure has expanded the range of 2D magnetic materials, a significant contribution has been made to the advancement of spintronics and its applications.