Experimental and first-principle studies of ferromagnetism in Na-doped SnO2 nanoparticles

Sn1−xNaxO2 nanoparticles (about 5 nm) have been successfully synthesized by a template-free hydrothermal growth method. XRD and XPS analyses reveal that the incorporated Na atoms substitute for Sn atoms in SnO2 lattice. The absorption spectra data show the band-gap decreases at low doping concentration (x ≤ 4%). With further doping, a transformation of Na atoms from substitutional sites to interstitial sites occurs. Magnetic measurements at room temperature showed a weak ferromagnetic behavior characterized by an open hysteresis loop. Their saturation magnetization MS increases initially with increasing Na concentrations and the largest saturation magnetization of 1.1 memu/g appears in Sn0.96Na0.04O2; however for x > 0.04, MS decreases. With the combination of defect analysis based on experimental results and first-principle calculations of the possible magnetic defect centers in Na-doped SnO2, the effect of defects on the nature and origin of ferromagnetism was investigated. The results suggest in Na-doped SnO2 nanoparticles the holes created by Na substituted incorporation may be the origin of the ferromagnetism in Na-doped SnO2 nanoparticles.