Effects of tetrahedral Fe2+ on the structural, magnetic and electronic properties of solution-based titanomagnetite thin films

Abstract

Polycrystalline titanomagnetite (Ti x Fe3−x O4) thin films prepared by using a sol-gel process exhibited a phase-pure spinel $$\left( {Fd\bar 3m} \right)$$ structure for Ti compositions up to x = 0.6. An X-ray photoelectron spectroscopy (XPS) investigation disclosed an increase of the Fe2+ concentration with increasing x, indicating a reduction in ionic valence, Fe3+ → Fe2+, induced by Ti4+ occupation of the cationic sublattice. Analyses on XPS and X-ray diffraction spectra of the Ti x Fe3−x O4 samples suggest that the Fe2+ ions prefer the tetrahedral sites while the Ti4+ ions prefer the octahedral sites of the sublattice. Magnetic hysteresis measurements on the Ti x Fe3−x O4 films revealed significant loss of the saturation magnetization (M s ) with increasing x: M s is reduced to 50% that of Fe3O4 for x = 0.10 and to 10% for x = 0.60. The big loss of M s caused by small Ti doping suggests a significant disruption of the inter-site Fe3+-Fe3+ super-exchange interaction in thin-film titanomagnetites.