Electronic property and topological phase transition in a graphene/CoBr₂ heterostructure

Recently, significant experimental advancements in achieving topological phases have been reported in van der Waals (vdW) heterostructures involving graphene. Here, using first-principles calculations, we investigate graphene/CoBr₂ (Gr/CoBr₂) heterostructures and find that an enhancement of in-plane magnetic anisotropy (IMA) energy in monolayer CoBr₂ can be accomplished by reducing the interlayer distance of the vdW heterostructures. In addition, we clarify that the enhancement of IMA energy primarily results from two factors: one is the weakness of the Co-d_xy and Co-d_x²–y² orbital hybridization and the other is the augmentation of the Co-d_yz and Co-d_z² orbital hybridization. Meanwhile, calculation results suggest that the Kosterlitz–Thouless phase transition temperature (T_KT) of a 2D XY magnet Gr/CoBr₂ (23.8 K) is higher than that of a 2D XY monolayer CoBr₂ (1.35 K). By decreasing the interlayer distances, the proximity effect is more pronounced and band splitting appears. Moreover, by taking into account spin–orbit coupling, a band gap of approximately 14.3 meV and the quantum anomalous Hall effect (QAHE) are attained by decreasing the interlayer distance by 1.0 Å. Inspired by the above conclusions, we design a topological field transistor device model. Our results support that the vdW interlayer distance can be used to modulate the IMA energy and QAHE of materials, providing a pathway for the development of new low-power spintronic devices.