Vacancy-Mediated Bound Magnetic Polarons as the Driving Mechanism for Ferromagnetism in Fe-Doped SnO₂ Nanowires

We report that room-temperature ferromagnetism in Fe-doped SnO₂ nanowires arises from the interaction between Fe³⁺ dopants and singly ionized oxygen vacancies (V_O'), mediated through bound magnetic polarons (BMPs). Combining experimental characterization with density functional theory (DFT), we demonstrate that although isolated oxygen vacancies are intrinsically nonmagnetic, their presence between Fe atoms stabilizes ferromagnetic coupling through shared BMP electrons. Raman spectroscopy and XPS confirmed the substitutional incorporation of Fe³⁺ into the SnO₂ lattice, while CL and EPR revealed the presence of oxygen-deficient environments and directly identified the singly ionized oxygen vacancy centers (V_O'), whose density increases with Fe incorporation. Magnetic measurements showed enhanced saturation magnetization and coercivity, directly correlated with V_O' signals. DFT calculations further supported these findings by identifying Fe-V_O-Fe complexes as the most stable configurations under O-rich conditions. This joint experimental-theoretical study provides microscopic evidence that vacancy-dopant interactions drive ferromagnetism in Fe-doped SnO₂ nanowires. The results highlight a defect-mediated mechanism that establishes oxide-based dilute magnetic semiconductors as promising candidates for spintronic applications.