Battisha, I. K. and Afify, H. H. and Hamada, I. M. (2005) Structural and magnetic susceptibility studies of SiO2: Fe2O3 nano-composites prepared by sol-gel technique. Journal of Magnetism and Magnetic Materials, 292 . 440 - 446.
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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 °C. Structural and magnetic characteristics were investigated through XRD, TEM, and magnetic susceptibility measurements. At 900 °C many γ-Fe2O3 crystalline nano-particles formed, while a further increase of the temperature resulted in the γ to α and/or ε: Fe2O3 transformation. By increasing the Fe2O3 content, the appearance of the α and/or ε phase is accompanied by a further growth of the γ phase. It seems, therefore, that the progressive γ-to-α and/or ε transformation is accompanied by a contemporary growth of the γ phase at the expense of the residual amorphous phase. The samples show low-magnetic susceptibility χT value typical to anti-ferromagnetic substances at lower sintering temperature ranging from 200 up to 700 °C, while transition to ferrimagnetic behavior is observed at higher sintering temperature ranging from 700 up to 1150 °C. It is clearly seen that between 700 and 900 °C, a broad transition occurs from anti-ferromagnetic amorphous phase to a ferrimagnetic one, corresponding to γ-Fe2O3. At constant sintering temperature 1150 °C the samples show lower magnetic susceptibility χT value at higher concentrations of Fe2O3 embedded in silica gel matrix. The observed behavior can be explained by the presence of γ-Fe2O3, whose contribution to the magnetic saturation at higher Fe2O3 content is much lower than that of α-Fe2O3 (and/or ε-Fe2O3) at this higher temperature.
|Subjects:||Physical Science > Nanomagnetics|
Material Science > Nanostructured materials
|Deposited On:||27 Jan 2009 14:56|
|Last Modified:||12 Feb 2009 12:08|
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