Synthesis of SiO 2 coated NiFe 2 O 4 nanoparticles and the effect of SiO 2 shell thickness on the magnetic properties J. Appl. Phys. 107, 09B523 (2010); 10.1063/1.3359426 Soft chemical synthesis and characterization of Ni 0.65 Zn 0.35 Fe 2 O 4 nanoparticlesNanocrystalline nickel ferrite (NiFe 2 O 4 ) 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. NiFe 2 O 4 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 NiFe 2 O 4 particles involves the nucleation of Fe 3 O 4 in amorphous silica at the initial stage of mechanical activation, followed by the growth of nickel ferrite by incorporation of Ni 2ϩ caions into Fe 3 O 4 . 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.