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.
Bibliographical noteFunding Information:
We acknowledge the partial financial support by Beijing Analyzing and Measuring Center. We also acknowledge the helpful discussions with Professor Wei Yu-Nian, Sun Ke, Feng Yuan-Bing and Dr Wang Gui-Hua. The assistance of Doctor Cai Jian-Wang is particularly acknowledged by Wang Jian-Ping.