${\text{SnO}}_2$ nanoparticles doped with Fe of different concentrations were synthesized by a chemical coprecipitation method. After calcination at $600°\text{C}$, the samples were characterized using x-ray diffraction (XRD), transmission electron microscope (TEM), and superconducting quantum interference device magnetometer. XRD shows that the solubility of Fe in ${\text{SnO}}_2$ (${\text{Sn}}_{1-x}{\text{Fe}}_x{\text{O}}_2$: primary phase where Fe substitutes Sn in ${\text{SnO}}_2$ matrix) is less than 7.5% $\left(x<0.075\right)$ and ${\text{Fe}}_2{\text{O}}_3$ (hematite) or ${\left({\text{Fe}}_{1-y}{\text{Sn}}_y\right)}_2{\text{O}}_3$ (where Sn substitutes Fe in ${\text{Fe}}_2{\text{O}}_3$ matrix) is evolved as a secondary phase for $x\ge 0.075$ along with ${\text{Sn}}_{1-x}{\text{Fe}}_x{\text{O}}_2$ (primary phase). TEM shows that the particles are crystalline and of size in the nanometric regime $\left(10\pm 3\text{nm}\right)$. The $M\left(T\right)$ and $M\left(H\right)$ studies indicated an antiferromagnetic (AFM) interaction in 3% and 5% (atomic weight) Fe-doped ${\text{SnO}}_2$ nanoparticles. The observed AFM interaction can be explained by the bound magnetic polaron model for insulating diluted magnetic semiconductor systems. It is seen that the strength of AFM interaction reduces with increase in doping concentration. On the other hand, 7.5% Fe-doped ${\text{SnO}}_2$ nanoparticles show the ferromagnetic interaction, but the origin of the observed ferromagnetism is identified due to the presence of ${\left({\text{Fe}}_{1-y}{\text{Sn}}_y\right)}_2{\text{O}}_3$ as a secondary phase.

• Received 28 February 2008

DOI:https://doi.org/10.1103/PhysRevB.78.024404