Development of high-temperature ferromagnetism in Sn O₂and paramagnetism in SnO by Fe doping

We report the development of room-temperature ferromagnetism in chemically synthesized powder samples of Sn_1-xFe_xO ₂(0.005≤x≤0.05) and paramagnetic behavior in an identically synthesized set of Sn_1-xFe_xO. The ferromagnetic Sn _0.99Fe_0.01O₂showed a Curie temperature T _C=850 K, which is among the highest reported for transition-metal- doped semiconductor oxides. With increasing Fe doping, the lattice parameters of Sn O₂decreased and the saturation magnetization increased, suggesting a strong structure-magnetic property relationship. When the Sn _0.95Fe_0.05O₂was prepared at different temperatures between 200 and 900 C, systematic changes in the magnetic properties were observed. Combined Mössbauer spectroscopy and magnetometry measurements showed a ferromagnetic behavior in Sn_0.95Fe _0.05O₂samples prepared at and above 350 C, but the ferromagnetic component decreased gradually as preparation temperature approached 600 C. All Sn_0.95Fe_0.05O₂samples prepared above 600 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. Mössbauer studies showed that the magnetically ordered Fe3⁺spins observed in the Sn_0.95Fe_0.05O₂sample prepared at 350 C is only ∼24% of the uniformly incorporated Fe3⁺. No evidence of any iron oxide impurity phases were detected in Sn_1-xFe_xO ₂or Sn_1-xFe_xO, suggesting that the emerging magnetic interactions in these systems are most likely related to the properties of the host systems Sn O₂and SnO, and their oxygen stoichiometry.