XANES, EXAFS, EPR, and First-Principles Modeling on Electronic Structure and Ferromagnetism in Mn Doped SnO2 Quantum Dots

The effect of Mn dopant on the electronic structure and magnetic properties of SnO₂ quantum dots was investigated using X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), electron paramagnetic resonance, and first-principles modeling. The results demonstrated that dilute Mn atoms substituted for Sn generates numerous oxygen vacancies. Interestingly, lower Mn doping concentration (2%) favored the formation of Mn³⁺ structures and increase of Mn doping to higher concentration (10% Mn) led to predominance of Mn³⁺ with a small fraction of Mn²⁺ configuration. The slight increase in bond length observed for 10% Mn doped SnO₂ QDs in EXAFS also corroborates with the XANES results where the absorption edge was shifted to lower energy, giving an indication of a very small presence of Mn in the +2 oxidation state. Electron paramagnetic resonance studies revealed the exchange coupled Mn interactions and also changes in distribution of local magnetic configurations with the increased dopant level of Mn. The considerable enhancement in the spin carrier density of states (DOS) and changes in the configuration of Mn upon variation in doping concentration in SnO₂ QDs demonstrate the effective role of Mn in modulating the electronic structure.