Nanocrystalline Maghemite (γ‐Fe ₂ O ₃ ) in Silica by Mechanical Activation of Precursors

γ‐Fe 2 O 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 3 O 4 in a highly activated matrix. Increasing the mechanical‐activation time led to a phase transformation from Fe 3 O 4 to γ‐Fe 2 O 3 . The γ‐Fe 2 O 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 2 O 3 . The mechanical‐activation‐grown γ‐Fe 2 O 3 nanocrystallites were ∼10–12 nm in size and well dispersed in the silica matrix, as observed using TEM. They demonstrated superparamagnetic behavior at room temperature when measured using a Mössbauer spectrometer and a vibrating sample magnetometer (VSM). In addition, the γ‐Fe 2 O 3 derived from 30 h of mechanical activation exhibited a value of saturation magnetization as high as 62.6 emu/g.