Abstract:

In this work, first-principles calculations were performed to study the effect of the adsorption of Fe atoms on the structure and properties of the WS₂ monolayer. It was found that the most stable adsorption site for an Fe atom on WS₂ at low coverage ( < 0.0625 ML) of the monolayer lies directly above the W atom and the atomic adsorption energy is ca. 1.84 eV. The interaction between the Fe and substrate atoms weakens the nearest W-S bonds which increases their bond length by ca. 0.011 nm. The orbital occupation of the adsorbed Fe atoms also undergoes redistribution. The 3d orbitals of Fe are fully occupied with the exception of the spin down channel of d_yz and d_xz orbitals. The magnetic interactions of Fe-Fe are mainly believed to involve super-exchange interactions which are mediated by the substrate. Thus the ferromagnetic order is unstable at low coverage. However, at high coverage, the distance between Fe-Fe decreases and the states close to the Fermi energy level induce magnetic interactions between the local magnetic moment and the itinerant electron, which are identified as RKKY interactions. In this manner, the ferromagnetic order is more stable at high coverage of the monolayer. The Density of state and band-structure calculations show that the spin polarization of Fe-WS₂ near the Fermi energy level is about 100%. The spin up channel acts as an indirect band gap semiconductor, while the another one acts as a metal. These calculations indicate that the Fe-WS₂ layer at high coverage could be half metallic, which can be potentially used to develop spin-based electronic materials.

Key words: DFT, Fe/WS₂, Transition metal dichalcogenides, Exchange interaction, Half-metal