Evidence of Bound Magnetic Polaron-Mediated Weak Ferromagnetism in co-doped SnO2 Nanocrystals: Microstructural, Optical, Hyperfine, and Magnetic Investigations

Abstract

Phase-pure rutile SnO2 nanoparticles doped with various pairs of transition metals such as Fe–Ni, Fe–Mn, Ni–Mn, and Co–Mn have been synthesized using a sol–gel method. Average crystallite size of 22 nm to 29 nm with no impurity secondary phase was observed by x-ray diffraction (XRD) analysis. The morphologies of the particles were studied and their sizes calculated by field-emission scanning electron microscopy (FESEM). Emission at 338 nm in photoluminescence (PL) spectroscopy was observed and attributed to band-edge emission, while the peak at 470 nm was ascribed to doubly ionized oxygen vacancies. Raman spectroscopy confirmed the phase purity of the sample. The effects of oxygen vacancies broaden the Eg mode of the Raman spectrum. In 119Sn Mossbauer spectra, broadened line width was observed and the singlet was attributed to Sn4+ valence state. The interaction between singly ionized oxygen vacancies and 3d dopant ion is the reason behind the ferromagnetic ordering observed in magnetic studies. Spins pinned at the surface orient randomly, which decreases the total moment.