Ferromagnetism in Defected TMD (MoX 2 , X = S, Se) Monolayer and Its Sustainability under O 2 , O 3 , and H 2 O Gas Exposure: DFT Study.

Spin-polarized density-functional theory (DFT) has been employed to study the effects of atmospheric gases on the electronic and magnetic properties of a defective transition-metal dichalcogenide (TMD) monolayer, MoX 2 with X = S or Se. This study focuses on three single vacancies: (i) molybdenum "V Mo "; (ii) chalcogenide "V X "; and (iii) di-chalcogenide "V X2 ". Five different samples of sizes ranging from 4 × 4 to 8 × 8 primitive cells (PCs) were considered in order to assess the effect of vacancy-vacancy interaction. The results showed that all defected samples were paramagnetic semiconductors, except in the case of V Mo in MoSe 2 , which yielded a magnetic moment of 3.99 μ B that was independent of the sample size. Moreover, the samples of MoSe 2 with V Mo and sizes of 4 × 4 and 5 × 5 PCs exhibited half-metallicity, where the spin-up state becomes conductive and is predominantly composed of dxy and dz2 orbital mixing attributed to Mo atoms located in the neighborhood of V Mo . The requirement for the establishment of half-metallicity is confirmed to be the provision of ferromagnetic-coupling (FMC) interactions between localized magnetic moments (such as V Mo ). The critical distance for the existence of FMC is estimated to be dc≅ 16 Å, which allows small sample sizes in MoSe 2 to exhibit half-metallicity while the FMC represents the ground state. The adsorption of atmospheric gases (H 2 O, O 2 , O 3 ) can drastically change the electronic and magnetic properties, for instance, it can demolish the half-metallicity characteristics. Hence, the maintenance of half-metallicity requires keeping the samples isolated from the atmosphere. We benchmarked our theoretical results with the available data in the literature throughout our study. The conditions that govern the appearance/disappearance of half-metallicity are of great relevance for spintronic device applications.