Development of high-temperature ferromagnetism in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Sn</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>and paramagnetism in SnO by Fe doping

We report the development of room-temperature ferromagnetism in chemically synthesized powder samples of ${\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{2}$ $(0.005\ensuremath{\leqslant}x\ensuremath{\leqslant}0.05)$ and paramagnetic behavior in an identically synthesized set of ${\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{O}$. The ferromagnetic ${\mathrm{Sn}}_{0.99}{\mathrm{Fe}}_{0.01}{\mathrm{O}}_{2}$ showed a Curie temperature ${T}_{C}=850\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which is among the highest reported for transition-metal-doped semiconductor oxides. With increasing Fe doping, the lattice parameters of $\mathrm{Sn}{\mathrm{O}}_{2}$ decreased and the saturation magnetization increased, suggesting a strong structure-magnetic property relationship. When the ${\mathrm{Sn}}_{0.95}{\mathrm{Fe}}_{0.05}{\mathrm{O}}_{2}$ was prepared at different temperatures between 200 and $900\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, systematic changes in the magnetic properties were observed. Combined M\"ossbauer spectroscopy and magnetometry measurements showed a ferromagnetic behavior in ${\mathrm{Sn}}_{0.95}{\mathrm{Fe}}_{0.05}{\mathrm{O}}_{2}$ samples prepared at and above $350\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, but the ferromagnetic component decreased gradually as preparation temperature approached $600\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. All ${\mathrm{Sn}}_{0.95}{\mathrm{Fe}}_{0.05}{\mathrm{O}}_{2}$ samples prepared above $600\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ were paramagnetic. X-ray photoelectron spectroscopy, magnetometry, and particle induced x-ray emission studies showed that the Fe dopants diffuse towards the surface of the particles in samples prepared at higher temperatures, gradually destroying the ferromagnetism. M\"ossbauer studies showed that the magnetically ordered ${\mathrm{Fe}}^{3+}$ spins observed in the ${\mathrm{Sn}}_{0.95}{\mathrm{Fe}}_{0.05}{\mathrm{O}}_{2}$ sample prepared at $350\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ is only $\ensuremath{\sim}24%$ of the uniformly incorporated ${\mathrm{Fe}}^{3+}$. No evidence of any iron oxide impurity phases were detected in ${\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{2}$ or ${\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{O}$, suggesting that the emerging magnetic interactions in these systems are most likely related to the properties of the host systems $\mathrm{Sn}{\mathrm{O}}_{2}$ and SnO, and their oxygen stoichiometry.