Effect of milling time on Fe/SiO2 system prepared by mechanical alloying

The evolution of structure during the mechanical milling of the Fe+SiO2 mixture has been studied. From X-ray diffraction line analyses we obtained the average grain size, crystalline weight fraction and lattice distortion for different milling times. The precursors milled are annealed at 1000 deg. C in air and characterized by their structure and magnetic properties. The heat treatment promotes the oxidation of Fe to hematite and some of magnetite. Thermal analysis at 1000 deg. C was also performed in argon atmosphere. Thermal treatment favours the formation of Fe2SiO4 and Fe3O4, in addition to the precursors Fe and SiO2. In this situation the annealing produces a compound with a coercivity of 78.2 emu/g, whereas the annealing in air atmosphere induces a mixture with a coercivity of 4.6 emu/g. The magnetization is explained in terms of the random anisotropy model (RAM)