Layer-dependent dopant stability and magnetic exchange coupling of iron-doped MoS2 nanosheets.

Using density-functional theory calculations including a Hubbard U term we explore structural stability, electronic and magnetic properties of Fe-doped MoS2 nanosheets. Unlike previous reports, the geometry and the stability of Fe dopant atoms in MoS2 nanosheets strongly depend on the chemical potential and the layer number of sheets. The substitution Fe dopant atoms at the Mo sites are energetically favorable in monolayer MoS2 and the formation of intercalated and substitutional Fe complexes are preferred in bilayer and multilayer ones under the S-rich regime that is a popular condition for the synthesis of MoS2 nanosheets. We find that the Fe dopants prefer to the ferromagnetic coupling in monolayer MoS2 and the antiferromagnetic coupling in bilayer and multilayer ones, suggesting the layer dependence of magnetic exchange coupling (MEC). The transition of MEC in Fe-doped MoS2 sheets induced by the change of layer number arises from the competition mechanism between the double-exchange and superexchange couplings. The findings provide a route to facilitate the design of MoS2-based diluted magnetic semiconductors and spintronic devices.