Room temperature ferromagnetism of bulk polycrystalline (In0.85-x SnxFe0.15)2O3: charge carrier mediated or oxygen vacancy mediated?

Four bulk polycrystalline (In0.85-xSnxFe 0.15)2 O3 samples with x=0, 0.01, 0.03, and 0.05 were synthesized, where carrier concentration n was controlled by varying Sn doping concentration x. Strong room temperature ferromagnetism was observed. A systematic characterization and analysis of structure, purity, magnetic, and transport properties indicates that ferromagnetism is due to neither impurities nor charge carriers. The four samples were annealed in air and high vacuum alternately. The ferromagnetism signal disappears and appears accordingly. Based on these results, we conclude that room temperature ferromagnetism in (In 0.85-xSnx Fe0.15)2O3 system is closely and directly related to oxygen vacancies in the samples.