INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
Low temperature Mössbauer and magnetic characterizations of (α-Fe2O3)1-x- (TiO2)x oxides
V. BILOVOL, A.M. MUDARRA NAVARRO, W.T.HERRERA, D.R.SÁNCHEZ, E.M.BAGGIO-SAITOVICH, C.E. RODRÍGUEZ TORRES, F.H. SÁNCHEZ AND A.F. CABRERA
Conferencia; XI Latin American Conference on the Applications of the Mössbauer Effect; 2008
Departamento de Física, Universidad Nacional de la Plata
Oxide dilute magnetic semiconductors (O-DMS), produced by doping nonmagnetic oxide semiconductors with transition metal atoms, are of interest for potential applications in spintronics. There is a continuous search of O-DMS which present ferromagnetic behavior above room temperature. Much work was done in the study of this kind of materials, but a real problem is to understand the origin of the observed magnetic behavior. This behavior is very dependent on synthesis condition of the samples and on their dimensionality (films or powders). In this work we explore the possibility of obtaining ferromagnetism in powder samples prepared by mechanical alloying from α-Fe2O3 and TiO2 oxides. Samples in appropriate concentrations (5, 10, 12.5 y 15 Fe at. %) were mechanically alloyed during 12 h in air at 30 Hz. The powders were characterized by X-ray diffraction (XRD), Mössbauer spectroscopy and magnetic measurements. The Mössbauer measurements were performed between room temperature (RT) and 4.2 K. All samples present the rutile structure, no evidence of precursor hematite was detected by XRD. In the RT Mössbauer spectra (MS) the Fe atoms have a paramagnetic behavior with 3+ and 2+ oxidation states for all samples, except for the 10 at. % one that reveals the existence of 3% of ordered hematite besides paramagnetic Fe3+. The low temperature MS display a magnetic splitting. Furthermore at 4.2 K, a fraction of Fe atoms in a 3+ paramagnetic state are still present for samples with 5, 10 and 12.5 at.% of Fe. The RT hysteresis loops show a paramagnetic signal and a small magnetically ordered contribution. In spite of the magnetic ordering observed in the MS at low temperature, no evidence of ferromagnetic order is found in the corresponding M vs H curves, indicating that the Fe atoms are ordered antiferromagnetically at low temperatures.