Structural Aspects of Fe<sub>3</sub>O<sub>4</sub>/CoFe<sub>2</sub>O<sub>4</sub> Magnetic Nanoparticles According to X-Ray and Neutron Scattering
Structural aspects of powders containing magnetic nanoparticles Fe<sub>3</sub>O<sub>4</sub>/CoFe<sub>2</sub>O<sub>4</sub> with the anticipated “core–shell” structure are considered by means of comparative analysis with individual particles of Fe<sub>3</sub>O<sub>4</sub>, CoFe<sub>2</sub>O<sub>4</sub> in accordance of data obtained from X-ray powder diffraction and small-angle scattering of X-ray (synchrotron) radiation and neutrons. It is shown that magnetic particles in the powders under study have a strong polydispersity and form complex aggregates. Characteristic sizes of the crystallites, as well as a ratio of magnetite to cobalt-ferrite in the composition of the Fe<sub>3</sub>O<sub>4</sub>/CoFe<sub>2</sub>O<sub>4</sub> particles were evaluated from the analysis of the diffraction peaks. Аnalyzing the data on small-angle scattering, the dimensional characteristics of particles and aggregates, as well as the volume fraction of the last ones in the powders, have been obtained. Fractal dimensions of aggregates are determined. A significant difference is observed in the scattering on Fe<sub>3</sub>O<sub>4</sub>/CoFe<sub>2</sub>O<sub>4</sub> particles and the total scattering consisting of partial contributions to scattering on individual magnetite (Fe<sub>3</sub>O<sub>4</sub>) and cobalt-ferrite (CoFe<sub>2</sub>O<sub>4</sub>) powders, which does not exclude the formation of the “core-shell” structure.