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 μB, 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.