Recent developments in the formation and structure of tin–iron oxides by laser pyrolysis

Complex oxides demonstrate specific electric and magnetic properties which make them suitable for a wide variety of applications, including dilute magnetic semiconductors for spin electronics. A tin–iron oxide Sn1−xFexO2 nanoparticulate material has been successfully synthesized by using the laser pyrolysis of tetramethyl tin–iron pentacarbonyl–air mixtures. Fe doping of SnO2 nanoparticles has been varied systematically in the 3–10 at% range. As determined by EDAX, the Fe/Sn ratio (in at%) in powders varied between 0.14 and 0.64. XRD studies of Sn1−xFexO2 nanoscale powders, revealed only structurally modified SnO2 due to the incorporation of Fe into the lattice mainly by substitutional changes. The substitution of Fe3+ in the Sn4+ positions (Fe3+ has smaller ionic radius as compared to the ionic radius of 0.69 Å for Sn4+) with the formation of a mixed oxide Sn1−xFexO2 is suggested. A lattice contraction consistent with the determined Fe/Sn atomic ratios was observed. The nanoparticle size decreases with the Fe doping (about 7 nm for the highest Fe content). Temperature dependent 57Fe Mössbauer spectroscopy data point to the additional presence of defected Fe3+-based oxide nanoclusters with blocking temperatures below 60 K. A new Fe phase presenting magnetic order at substantially higher temperatures was evidenced and assigned to a new type of magnetism relating to the dispersed Fe ions into the SnO2 matrix.