Room-temperature ferromagnetism in multilayered VSe ₂ and defect–strain correlations

Abstract Two-dimensional vanadium diselenide (VSe ₂ ) has demonstrated potential ferromagnetic ordering at the few-layer limit under ambient conditions; however, the fundamental origin of this room-temperature ferromagnetism remains unclear. While some studies attribute the observed magnetism to extrinsic factors such as selenium vacancies or strain, others suggest it arises intrinsically from spin–spin interactions involving the 2d ¹ electron of the V ³⁺ ion. Here, we report the observation of room-temperature ferromagnetism in ∼300 nm-thick VSe ₂ flakes, which is 30x thicker than any previous report measured by SQUID magnetometry. Our results show a clear in-plane hysteresis loop at 300 K. To understand the underlying origin of this ferromagnetism, we performed density-functional theory calculations and toy-model simulations correlating selenium vacancy concentration with local lattice strain. By introducing 1%–10% Se vacancies in a 2 × 2 supercell, we observe a local in-plane tensile distortion that nearly doubles the magnetic moment (peak Δ M ≈ 2× at 10% vacancy). Additionally, strain-only calculations show that tensile in-plane strain enhances the magnetic moment, indicating that both homogeneous strain and vacancy-induced local distortions provide tunable routes to engineer magnetism in VSe ₂ .