Magnetism Induced by Azanide and Ammonia Adsorption in Defective Molybdenum Disulfide and Diselenide: A First-Principles Study

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention due to their tunable structural, electronic, and spin-related properties, particularly in the presence of point defects and molecular adsorbates. Motivated by these aspects, we have investigated using first-principles methods, the magnetic properties induced by azanide (NH₂) and ammonia (NH₃) adsorption on defective monolayers of molybdenum disulfide (MoS₂) and molybdenum diselenide (MoSe₂). Spin-polarized density functional theory (DFT) at the generalized gradient approximation (GGA) level, using the Perdew-Burke-Ernzerhof (PBE) functional, was employed to investigate the impact of mono- and divacancies on the local spin environment and the role of molecular adsorption in modifying magnetic behavior. The results show that pristine chalcogen vacancies do not generate magnetism, whereas the adsorption of NH₂ and NH₃ creates localized magnetic moments in Mo-based dichalcogenides. A notable case occurs for MoSe₂, where NH₃ dissociation into NH₂ and H fragments on the same side of the surface produces a net magnetic moment of 2.0 μ_B. Tests performed on W-based dichalcogenides under equivalent conditions showed no magnetic response and are reported here only for comparison. These findings demonstrate that molecular adsorption combined with defect engineering can be a practical approach to tune magnetism in 2D materials, with potential relevance for spintronic and sensing applications.