$NiFe2O4$ nanoparticles formed in situ in silica matrix by mechanical activation

Nanocrystalline nickel ferrite $(NiFe2O4)$ particles were successfully synthesized in situ in an amorphous silica matrix by mechanical activation at room temperature. Phase development in the amorphous precursors, derived via a modified sol–gel synthesis route, with increasing mechanical activation time was studied in detail by employing transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. $NiFe2O4$ nanoparticles of 8.05 nm in mean particle size with a standard deviation of 1.24 nm, which were well dispersed in the silica matrix, were realized by 30 h of mechanical activation. The phase formation of nanocrystalline $NiFe2O4$ particles involves the nucleation of $Fe3O4$ in amorphous silica at the initial stage of mechanical activation, followed by the growth of nickel ferrite by incorporation of $Ni2+$ caions into $Fe3O4.$ Their magnetic anisotropy, surface spin disorder, and cation distribution are investigated by considering both the strain imposed by silica matrix and the buffer effect during mechanical activation.