Preparation and properties of pure nanocomposite Fe-SiO₂ using the sol-gel method

Pure nanocomposite Fe-SiO₂ has been prepared by the sol-gel method, which is capable of producing large quantities of nanocomposite material. The average diameter of iron particles ranged from several nanometers to tens of nanometers, which can be controlled by the iron concentration and calcining temperature. The results of X-ray diffraction and Mössbauer spectra showed that the nonferromagnetic phase Fe₂SiO₄ is formed when the iron concentration is beyond about 16 wt% for the samples reduced at 700°C for 4 h. The dependence of the magnetization of iron in Fe-SiO₂ on iron concentration between 1 and 33 wt% was studied for samples reduced at 700°C for 4 h. The dependence of saturation magnetization of iron on temperature between 1.5 and 300 K was measured using an extracting-sample magnetometer for a 2.5 wt% Fe Fe-SiO₂ sample reduced at 700°C for 4 h. A very sharp increase in magnetization was observed when the temperature was below about 40 K. The magnetization dependence on temperature has been well fitted by Bloch's law when the temperature is above 150 K, and the Bloch constant fitted from experimental data is 2.33 × 10^-5 K ^{2 3}, far larger than the value of 3.3 × 10^-6 K ^{2 3} for bulk iron.