First-Principles Calculations of Room-Temperature Ferromagnetic Half-Metallicity and Quantum Anomalous Effect in 2D NbX₂ (X = S, Se, Te) Monolayers: Implications for Spintronic Nanodevices

The development of two-dimensional (2D) ferromagnetic half-metals with 100% spin polarization provides a broad platform for exploring the nanoscales. Herein, based on first-principles calculations, we report one type of 2D transition metal chalcogenides, NbX 2 (X = S, Se, Te), with high thermodynamic stability. It is found that NbS 2, NbSe 2, and NbTe 2 monolayers are robust ferromagnetic half-metals with above room-temperature Curie temperature and considerable band gaps in the semiconducting spin channels (larger than 1.0 eV). In particular, both NbSe 2 and NbTe 2 monolayers are turned to be Quantum Anomalous Hall (QAH) metals with a nonzero Chern number of | C | = 1 on the basis of the spin orbit coupling (SOC) effect. In addition, applying biaxial tensile strains in NbSe 2 and NbTe 2 can induce a transition from ferromagnetic half-metals to ferromagnetic semiconductors. Our study proposes that the NbX 2 (X = S, Se, Te) monolayers are potential candidates in room-temperature spintronics devices.