NiX2 (X = Cl and Br) sheets as promising spin materials: a first-principles study

Abstract

In order to achieve paper-like spin devices, it is rather critical to develop new two-dimensional (2D) spin materials. In this study, the geometrical structure, stability, and electronic and magnetic properties of 2D nickel dihalides of NiX₂ (X = Cl and Br) type were investigated using density functional theory (DFT) calculations. We found that after optimization, geometries of NiCl₂ and NiBr₂ sheets that are obtained from their bulk counterparts are well kept. Phonon dispersion calculations demonstrated that both NiCl₂ and NiBr₂ sheets are dynamically stable. Magnetism calculations showed that ferromagnetic (FM) coupling is ground state for both structures in which per NiCl₂ and NiBr₂ unit cells can possess the moments of 1.91 and 1.88 μ_B, respectively. Density of states (DOS) and band structure calculations revealed that both structures are magnetic semiconductors with large band gaps. In addition, strain effect also showed that the moments of NiCl₂ and NiBr₂ sheets can be effectively tuned by applying the biaxial strain. A unique combination of integrated geometry, dynamical stability, intrinsic ferromagnetism, a magnetic semiconductor and tunable magnetism makes NiCl₂ and NiBr₂ sheets promising candidates for next-generation paper-like spin devices.