K.G. Gareev - Post-graduate Student, Saint-Petersburg State Electrotechnical University «LETI» n. a. V. I. Ulyanov (Lenin)
I.E. Kononova - Research Scientist, Saint-Petersburg State Electrotechnical University «LETI» n. a. V. I. Ulyanov (Lenin)
V.A. Moshnikov - Dr.Sc. (Phys.-Math.), Professor, Saint-Petersburg State Electrotechnical University «LETI» n. a. V. I. Ulyanov (Lenin)

The article studies colloids of magnetic nanoparticles obtained by depositing a layer of magnetite onto nanostructured sol-gel silica. An investigation of the layers was performed by atomic force microscopy and X-ray analysis. SiO2 fine powder was analyzed by thermal desorption for determining specific surface area. On the basis of microscopy data particle size distribution was estimated. The study showed the possibility tosynthesize aggregative stable aqueous colloidal solutions of Fe3O4/SiO2nanoparticles. Under the influence of external factors, in particular a constant magnetic field induction of more than 10 mTa formation of linear aggregates of particles elongated along the field lines is observed. It was revealed that in the presence of 1 mT magnetic field fractal aggregates were formed, whose growth based on the model of diffusion- limited aggregation of naturally occurring concurrently with the random nature of the cluster-cluster aggregation. The article describes the effect of the concentration of tetraethoxysilane on the value of the specific surface area of silica. When the content of TEOS is in 60-80 % range SiO2 powders are characterized by maximum SSA. Calculating of SiO2 mean particle size from these data yields a value of about 50 nm at 40 vol. % and less TEOS, and more than 100 nm at 90 vol. % , which is consistent with the results of atomic force microscopy.