Cobalt ferrite (CoFe2O4) nanoparticles were successfully prepared in situ in an amorphous silicon matrix by sal-gel method. The magnetic and structural properties of the powders were investigated by varying the annealing temperature and the weight ratio of cobalt ferrite and silica. The samples, with 40 wt.% cobalt ferrite annealed at 873 K and above, are found in a single spinel phase structure and behave ferrimagnetically. However, the samples annealed below 773 K show superparamagnetic behavior. The magnetic parameters, such as saturation magnetization (Ms), remanent magnetization (Mr) and coercivity (Hc), increase monotonically with annealing temperature with the corresponding maximums of 21.09 emu g(-1), 5.671 emug g(-1) and 1.15 kOe, respectively. The samples annealed at 1073 K are ferro-magetic, except for the one with 10 wt.% cobalt ferrite, which is superparamagnetic. The corresponding maximum is 34.28 emu g(-1), 10.41 emu g(-1) and 1207 Oe, respectively. The Ms and Mr increase with content of cobalt ferrite, except for the Hc values. The isomer shifts show that the iron atoms are ferric at the tetrahedral (A) and the octahedral (B). The nature of magnetic phase was analyzed by Mossbauer spectra. (C) 2010 Elsevier B.V. All rights reserved.