Nanocrystalline maghemite (γ-Fe 2O 3) in silica by mechanical activation of precursors

Abstract

γ-Fe 2O 3 nanocrystallites dispersed in an amorphous silica matrix have been successfully prepared for the first time by mechanical activation of a chemistry-derived precursor at room temperature. The initial 10 h of mechanical activation triggered the formation of nanocrystallites of Fe 3O 4 in a highly activated matrix. Increasing the mechanical-activation time led to a phase transformation from Fe 3O 4 to γ-Fe 2O 3. The γ-Fe 2O 3 phase was well established after mechanical activation of the precursor for 30 h. Further increasing the mechanical-activation time to 40 h induced the formation of α-Fe 2O 3. The mechanical-activation-grown γ-Fe 2O 3 nanocrystallites were ∼10-12 nm in size and well dispersed in the silica matrix, as observed using TEM. They demonstrated super-paramagnetic behavior at room temperature when measured using a Mössbauer spectrometer and a vibrating sample magnetometer (VSM). In addition, the γ-Fe 2O 3 derived from 30 h of mechanical activation exhibited a value of saturation magnetization as high as 62.6 emu/g.