Structural and magnetic susceptibility studies of SiO2 : Fe2O3 nano-composites prepared by sol-gel technique

• Published in: Journal of magnetism and magnetic materials 2005-04, Vol.292, p.440-446
• Main Authors: BATTISHA, I. K, AFIFY, H. H, HAMADA, I. M
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Magnetic properties and materials; Magnetic properties of nanostructures; Physics
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2004.10.121

Silica gel doped with different concentrations of Fe2O3 ranging from 5 up to 40 wt% (SiO2: 5-40 wt% Fe2O3) was prepared by sol-gel method, using tetra-ethoxysilane as precursor material. The prepared samples were submitted to thermal treatments in the temperature range from room temperature (RT) up to 1150 deg C. Structural and magnetic characteristics were investigated through XRD, TEM, and magnetic susceptibility measurements. At 900 deg C many ygammaFe2O3 crystalline nano-particles formed, while a further increase of the temperature resulted in the D*g to D*a and/or epsilon Fe2O3 transformation. By increasing the Fe2O3 content, the appearance of the alpha and/or gamma phase is accompanied by a further growth of the gamma phase. It seems, therefore, that the progressive gamma-to-alpha and/or epsilon transformation is accompanied by a contemporary growth of the gamma phase at the expense of the residual amorphous phase. The samples show low-magnetic susceptibility XT value typical to anti-ferromagnetic substances at lower sintering temperature ranging from 200 up to 700 DGC, while transition to ferrimagnetic behavior is observed at higher sintering temperature ranging from 700 up to 1 150 DGC. It is clearly seen that between 700 and 900 DGC, a broad transition occurs from anti-ferromagnetic amorphous phase to a ferrimagnetic one, corresponding to gamma-Fe2O3. At constant sintering temperature 1150 DGC the samples show lower magnetic susceptibility gammaT value at higher concentrations of Fe2O3 embedded in silica gel matrix. The observed behavior can be explained by the presence of gamma-Fe2O3, whose contribution to the magnetic saturation at higher Fe2O3 content is much lower than that of alpha-Fe2O3 (and/or epsilon-Fe2O3) at this higher temperature.