Engineering the ligand states by surface functionalization: a new way to enhance the ferromagnetism of CrI ₃

The newly discovered 2D magnetic materials provide new opportunities for basic physics research and device applications. However, their low Curie temperature (TC) is a common weakness. In this paper, by combining magnetic Hamiltonian, Wannier functions and first-principles calculations, we systematically study the magnetic properties of monolayer CrI3 functionalized with halogens. The magnetic exchange coupling (EX) and magnetic anisotropy (MA) are found to increase significantly with X (X = F, Cl and Br) atom adsorption, and increase with increased coverage of X. In the framework of superexchange theory, the enhanced EX can be ascribed to the reduced energy difference and increased hopping strength between Cr d and I p orbitals, due to the states of the I ligand engineered by the X adatom. Besides, the X adatom may provide an additional ferromagnetic superexchange channel. Our results not only give insight into understanding the enhancement of ferromagnetism of CrI3 by atom adsorption, but also propose a promising way to improve the ferromagnetism of 2D magnetic materials.