Paramagnetism and clustering in Fe-doped TiO2 nanoparticles

C. ADÁN, A. F. CABRERA, C. E. RODRÍGUEZ-TORRES AND S. J. STEWART

Buenos Aires, Argentina

Congreso; XV International Symposium on Metastable, Amorphous and nanostructured materials (ISMANAM); 2008

Systems composed by the dilution of magnetic ions in semiconductor non-magnetic matrices (DMS) have attracted considerable interest in the last years due to potential application in spintronic devices. As the ferromagnetic signal with Curie temperatures above room temperature were mainly detected in thin films systems (e. g. Fe/Co doped TiO2) it seems that spatial dimensionality might play an important role. Therefore, it is also interesting to investigate how the reduction of the structural correlation length down to the nanoscale range might influence on the DMS magnetic behaviour. Previously, we found that in Fe-doped TiO2 nanoparticles, where iron (III) replaces titanium (IV) in the anatase structure, these iron ions are in a paramagnetic state at room temperature [1]. By analyzing the thermal evolution of the hysteresis loops we demonstrate here that for low Fe concentration ( £ 2.5 at. %) the iron ions remain paramagnetic down to T= 2K while for the more concentrated sample (5.4 at. %) the emergence of magnetically isolated clusters is clearly favored. This fact is evident from the analysis of the evolution of the hysteresis loops where the fraction of paramagnetic irons extracted from the fits using the Brillouin function decrease with temperature.  In this work we showed such evolution in samples with Fe concentration within 1 and 5 %.