Structural and magnetic study of (a-Fe2O3)x – (TiO2)1-x

V. BILOVOL, A.M. MUDARRA NAVARRO, C.E. RODRIGUEZ TORRES, F.H. SANCHEZ, A.F.CABRERA

Rio de Janeiro, Brazil

Conferencia; 9th International Conference on Nanostructured Materials; 2008

TiO2 oxide doped with transition metals could present ferromagnetism at room temperature, which make 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 performance has 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 the study of Fe-doped TiO2 by means of Mossbauer spectroscopy and XAS. These techniques allow us characterize the local doping environment and relate it with the magnetic behaviour.  Powders of á-Fe2O3 and TiO2 in appropriate concentrations (2.5, 5, 7, 10 y 15 Fe at %) were mechanical alloyed during 12 h in air. The samples were characterized by Mossbauer 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 Fe0.13Ti0.81O1.92 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 concentration while other paramagnetic contribution (oxidation sates 2+) appears for lower concentrations.  The hysteresis loops at room temperature show the coexistence of two magnetic phases, one ordered and the other disordered in spite that the observed by MS. The results indicate that the initial hematite disappears and that the Fe atoms mix with the Ti ones forming ternary oxides.