New data on gallium ferrite particles are reported. The results of studies of Fe3O4/GaxFe3 – xO4 and GaxFe3 – xO4/Fe3O4 (x = 0.2, 0.4, 0.6 and 0.8) nanoparticles by X-ray and neutron diffraction, small angle neutron scattering, transmission electron microscopy, magnetization measurements, and Mössbauer spectroscopy. The cubic core–shell ferrites structures were confirmed as single phases with a cell parameter of ∼8.388 Å independent of gallium content. The lack of preferences in occupancies of gallium sites was confirmed. The magnetic structure at room temperature, the stability of a disaggregated dispersion of nanoparticles in the temperature range 20–50°C, the radii of the cores, and the thickness of the coating layers, as well as the specific absorption of electromagnetic radiation rates were characterized