Modulation of magnetism in transition-metal-doped two-dimensional GeS

Abstract

Two-dimensional (2D) germanium monosulfide (GeS) is a promising nanoelectronic material with a desirable band gap, high carrier mobility, and anisotropic structures. In this work, we present a density functional theory study on the magnetism of 3d TM (TM = Fe, Co and Ni)-doped 2D GeS. We find that the TM atoms strongly bond to the GeS sheet with quite sizable binding energies due to the sp3-like hybridization of 2D GeS. The Fe- and Co-doped GeS show nonzero magnetic ground states. Hubbard parameter U hardly affects the magnetic moment when U is no more than 6 eV. In particular, substitutional Fe (Fe@GeS) and substitutional Co (Co@GeS) present high-spin states with 4 μB and 3 μB. The magnetism of TM-doped 2D GeS mainly arises from the crystal field splitting and spin exchange splitting of TM-3d orbitals. The magnetic and electronic properties of the Fe@GeS and Co@GeS systems can be easily controlled in a small vertical external electric field (Eext). The underlying mechanism of spin crossover is that Eext affects the crystal field splitting and then shifts the relative positions of 3d orbitals, which tunes the spin configurations. These results render monolayer GeS a promising 2D material for applications in future spintronics.