Structural, optical and magnetic properties of γ-irradiated SiO2 xerogel doped Fe2O3

The paper deals with the structure, morphology and magnetic properties of two different iron concentrations (20 and 33 mol.%) of Fe2O3-SiO2 nanocomposites, prepared by sol-gel technique and exposed to different gamma-irradiation doses (0, 30 and 60 kGy). The nanocomposites were investigated through XRD, TEM, SEM, FTIR and EPR measurements. Superparamagnetic iron (III) oxide nanoparticles with a narrow size distribution, dispersed over the amorphous silica matrix, are assumed to be present in all the samples before and after irradiation. Before irradiation, a lot of γ-Fe2O3 crystalline ferromagnetic nanoparticles are assumed to be formed particularly for sample containing 33 mol.% Fe2O3, while exposing the samples to irradiation results in the transformation of γ- to α-Fe2O3. Iron concentrations and/or irradiation of the samples are assumed to cause changes in the bond angles and/or bond lengths of the structural silicate units within network, as well, the increase of more defect centers induced by irradiation as evident through the variations of the IR bands intensity. The EPR results show both intensity and line width increase with increasing Fe2O3 concentration. The EPR signals for the samples consist of a well defined symmetrical broad signal at g≈2.0 ascribed to antiferromagnetic interactions between the Fe(2+) and Fe(3+) clusters. Condensed clusters of Fe(3+) ions are observed to give rise to a resonance line at g∼2 whose position and width do not depend on the Fe2O3 concentrations. The EPR signal intensity is observed to be significantly decreased in the sample 33 mol.% or stabilized in the sample 20 mol.% by γ-irradiation. This reflects simultaneous spin transformation from the high-spin state of Fe III to the low-spin state of Fe II. As a final point, an effort has been given to found the possibility to use one of these studied nanocomposite materials as candidate for radiation shielding purposes.