First-Principles Study of the Electronic and Magnetic Properties of Fe-Doped MoS₂ Monolayer via Sulfur Vacancy Engineering using Density Functional Theory

Abstract

Two dimensional transition metal dichalcogenides are a game changing class of nanomaterials for nanoscale spin dependent transport devices, but the intrinsic non-magnetic diamagnetic properties of pristine molybdenum disulfide (MoS₂) greatly limit its operational viability. Here, in a systematic investigation, we conduct rigorous first-principles calculations with spin-polarized density functional theory (DFT) in combination with on-site Hubbard Coulomb interactions (DFT+U), to systematically study the synergy between substitutional Fe doping (Fe_Mo) and spatial engineering of S vacancy (V_S) defects in a MoS₂ monolayer. The results of thermodynamic evaluations show that the localized formation energy of a sulfur vacancy, located next to a Fe incorporated center, is greatly reduced to 1.12 eV under Mo-rich growth conditions, suggesting a strong thermodynamic driving force in the form of defect trapping. The electronic bandstructure and orbital-projected density of states analyses show that the pristine direct band gap of 1.73 eV turns into an ideal half-metallic ground state with 100% spin polarization at the Fermi level when the Fe dopant is connected to a nearest neighbour sulfur vacancy. The structural change breaks the local D_3h crystal field symmetry down to C_3v, and causes the degeneracy of the Fe-3d orbitals to break, transforming the electronic spin state from low spin . In addition, the calculations also account for spin-orbit interactions, giving rise to strong perpendicular magnetocrystalline anisotropy (+2.14 meV per Fe atom), and Monte Carlo simulations using a classical Heisenberg model also predict a ferromagnetic Curie transition at room temperature, in which the transition is mediated by vacancy-assisted double-exchange interactions (348 K).