Characterization of iron magnetic nanoparticles by termomagnetogravimetry,

J. C. APHESTEGUY, C. E. RODRÍGUEZ TORRESB, M.B. FERNÁNDEZ VAN RAAP, S. E. JACOBO, Y F. H. SÁNCHE

Buenos Aires, Argentina

Congreso; Amorphous and nanostructured materials (ISMANAM); 2008

Along the last two decades we have witnessed considerable achievements related to the design of magnetic nanostructures, aiming both basic research and technological applications. Nanoparticles with super-paramagnetic properties have great potential to achieve such desirable properties. Various methods have been developed to synthesize iron oxide particles in nanometer size range [1-3]. These genuine improvements of fabrication techniques have not been accompanied by a detailed comprehension of the relationships between structural and magnetic properties in fine particle systems, even those composed of ‘simple’ materials as magnetite and maghemite whose bulk properties are well understood.Magnetite (Fe3O4) and Maghemite (γ-Fe2O3) phases are isostructural, with nearly the same lattice parameter, then X-ray diffraction (XRD) cannot differentiate between them, especially in the nanophase state. Although Mössbauer spectroscopy in bulk material can clearly identify the two oxides, owing to the presence of divalent iron in magnetite, in the case of nanophase state, the spectrum displays broadened and asymmetric lines due to the surface contribution making their identification difficult. Then additional techniques are necessary in order to characterize the oxide nanoparticles.Here, we report on the preparation and characterization of iron magnetic nanoparticles, where besides XRD and Mössbauer spectroscopy, Thermogravimetric (TG) measurements performed in the presence of a magnetic field (Termomagneto-gravimetry, TMG) are used to identify the phases. XRD patterns of prepared nanoparticles are typical of an inverse spinel structure, meaning the formation of either magnetite or maghemite. Their ME spectrum presents the main characteristics of γ-Fe2O3: a symmetric spectrum with a mean isomer shift value of 0.33 mm/s, corresponding to Fe3+. However the TMG measurement of this sample displays a main feature at 273 °C which was observed in commercial magnetite but not in maghemite.