A variable temperature Fe3+ electron paramagnetic resonance study of Sn1-x Fex O2 (0.00≤x≤0.05)

X -band (∼9.5 GHz) electron paramagnetic resonance (EPR) studies of Fe3+ ions in Sn1-x Fex O2 powders with 0.00≤x≤0.05 at various temperatures (5-300 K) are reported. These samples are interesting to investigate as Fe doping (≤5%) produces ferromagnetism in Sn O2 [A. Punnooose, Phys. Rev. B 72, 054402 (2005)], making it a promising ferromagnetic semiconductor at room temperature. The EPR spectrum at 5 K can be simulated reasonably well as the overlap of spectra due to seven magnetically inequivalent Fe3+ ions: four low-spin (S=12) and three high-spin (S=52) ions, characterized by different spin-Hamiltonian parameters, overlapped by three broad ferromagnetic resonance spectra. The three high-spin ions, situated substitutionally in the interior of nanodomains, are characterized by smaller zero-field splitting (ZFS) parameters D and E, so that all their energy levels are populated at 5 K. On the other hand, the four low-spin ions are situated interstitially at the surfaces of nanodomains. They are characterized by much larger ZFS, so that only their lowest Kramers doublets are occupied at 5 K. Based on this simulation, it is concluded that the observed spectra at different temperatures can be reproduced by changing appropriately the relative overlaps of the various paramagnetic and ferromagnetic characters, which remain present over the temperature range studied.