Correlation of structural behavior of 3 and 9 nm iron oxide nanoparticles: the role of the surface/volume ratio

MOSCOSO-LONDOÑO. O; LEDE. E. J; C. COSIO-CASTAÑEDA; RICARDO MARTÍNEZ GARCÍA; SOCOLOVSKY. L. M

Encuentro; LNLS 23rd ANNUAL USERS MEETING; 2013

Iron oxide nanoparticles have attracted much research attention due to their remarkable technological and biomedical applications. Particularly the miniaturization of iron oxides displays novel properties resulting from the surface or quantum size effects. In this work we present the influence of the surface/volume ratio on magnetic and structural properties of 3 nm and 9 nm γ-Fe2O3 nanoparticles, which were synthetized by the coprecipitation method. The magnetic experiments (no show here) on 3nm iron oxide nanoparticles as function of temperature using a superconducting quantum interference device (SQUID) show in the MZFC(T) a typical curve of both superparamagnetic (SPM) and superspin glass (SSG) systems. Experiments XAFS were performed at 10K in the beamline XAFS1-LNLS. The absorption spectra were taken with X-ray energies in the range 6954-8057 eV and were obtained in the transmission mode in the Fe K-edge (7112 eV). In the EXAFS region the absorption spectra for 3nm and 9 nm γ-Fe2O3reveal a characteristic signal composed by a contribution of the first O neighbors and second neighbors O and Fe. The Fourier transform (FT) of the signal in each case clearly shows an intense and characteristic peak, generated by oxygen atoms in the first coordination sphere of the Fe (0.83-2.1 Å).The less intense peaks can be associated with more distant neighbors (2.1-3.5 Å).These peaks, corresponding to the second coordination sphere, increase in intensity when the particle size is increased. This would be indicating an increase in average coordination number and a greater order in the medium range for the case of 9 nm γ-Fe2O3 in comparison with 3 nm γ-Fe2O3.