Structural and magnetic study of (alfa-Fe2O3)x-(TiO2)1-x oxides

V. BILOVOL, A.M. MUDARRA NAVARRO, C.E. RODRÍGUEZ TORRES, F. H. SÁNCHEZ AND A.F. CABRERA

Rio de Janeiro, Brasil

Conferencia; 9th International Conference on Nanostructured Materials; 2008

TiO2 oxide doped with transition metals could present ferromagnetism at room temperature, which makes this type of materials suitable for potential technological applications.  Actually the origin and nature of the observed magnetic behaviour in this doped oxide are not totally understood. Furthermore different magnetic performances have been reported for the oxide doped with the same doping concentration depending on the sample preparation methods.  In addition, the local impurity environment could play an important role in the observed magnetic behaviour.  In this work we report on the study of Fe-doped TiO2 by means of Mössbauer spectroscopy and X-ray absorption spectroscopy (XAS). These techniques allow us to characterize the local doping environment and relate it to the magnetic behaviour.  Powders of α-Fe2O3 and TiO2 in appropriate concentrations (2.5, 5, 7, 10 and 15 Fe at %) were mechanically alloyed during 12 h in air. The samples were characterized by Mössbauer spectroscopy (MS), XAS (EXAFS and XANES), X-ray diffraction (XRD) and magnetization versus applied field. Two phases are detected by XRD, rutile TiO2 and orthorhombic FeyTi1-yO2-δ (y=0.13, [1]) which are present in all samples. The XAS characterization indicates that the majority of Fe atoms have a local environment similar to the Ti ones in the rutile structure. By MS, the Fe atoms are paramagnetic with oxidation state 3+ for higher concentrations while other paramagnetic contribution (oxidation state 2+) appears for lower concentrations.  The hysteresis loops at room temperature show the coexistence of two magnetic phases, one disordered and the other ordered in spite to what was observed by MS. The results indicate that the initial hematite disappears and that the Fe atoms mix with the Ti ones forming ternary oxides.   [1] L.A. Bursill, I.E. Grey, D.J. Lloyd, J.Sol. Stat. Chem. 16 (3-4) (1976) 331   This work was supported by ANCYPT and CONICET (PIP 6005). The magnetization measurement were done with the facilities of the Red Nacional de Magnetismo y Materiales Magnéticos