Structural, optical, magnetic, and XPS properties of SnO_x nanoparticles

SnOx nanoparticles ranging in average particle sizes from 13 to 420 nm have been prepared by levitation-jet aerosol synthesis through condensation of tin vapor in a mixed flow of inert gases and air/oxygen. X-ray diffraction (XRD) established the presence of mixed-phase of Sn, SnO, and SnO2 components in the nanoparticles. During optical measurements, the redshift of bandgaps was discovered in nanoparticles with SnO2 content < 80% and blue shift in nanoparticles with SnO2 content > 80%. The samples were examined for their magnetic properties using a vibrating sample magnetometer (VSM) and indicate room-temperature ferromagnetism. The maximum net saturation magnetization observed in the studied nanoparticles is & AP;7 memu/g near a Sn/O molar ratio of & AP;0.58. Moreover, an excess magnetic contribution (from oxygen vacancies), either as paramagnetic or as diamagnetic susceptibility, has been observed. Raman studies found the presence of small amounts of Sn3O4 or Sn2O3 phases in the nanoparticles. The presence of oxygen vacancies in the nanoparticles was established by Xray photoelectron spectroscopy (XPS). Their density increase is probably accompanied by the saturation magnetization enhancement. We propose that the presence of definite localized states, like interacting and non interacting vacancies on the Sn/SnO and SnO/SnO2 interfaces, is responsible for the observed magnetic phenomena.