Defect-induced ferromagnetism in bulk VSe₂

Vanadium diselenide (VSe₂), a layered transition metal dichalcogenide with 1T and 2H phases, is a promising material for spintronic applications due to its intrinsic magnetic property. Ferromagnetism in VSe₂ has been experimentally observed only in the monolayer limit, while its bulk form is considered nonmagnetic. Using spin-polarized density functional theory (DFT+U) calculations, we investigate the role of selenium vacancies for electronic and magnetic properties of bulk VSe₂. Consistent with experimental observations, the pristine 1T and 2H phases are metallic and semiconducting, respectively, and both are nonmagnetic. Introduction of Se vacancies induces V-V dimerization and a transition from nonmagnetic to ferromagnetic behavior around the stoichiometry of VSe_1.75. This transition is driven by defect-induced charge redistribution and the formation of mixed-valence V⁴⁺/V³⁺ states that enhance double-exchange interactions. The emergence of magnetism in defective samples is further supported by magnetic measurements. These results demonstrate that controlled defect engineering can stabilize ferromagnetism in bulk VSe₂, opening opportunities for spintronics applications.