The highly dispersed nickel ferrites NixFe3-xO4 (x = 0.25, 0.5, 0.75, 1.0, 1.5) were obtained by a two-step method involving coprecipitation and treatment with contact low-temperature nonequilibrium plasma (CNP). The synthesized nanoparticles were studied using an X-ray diffractometer, a scanning electron microscope and a vibrational magnetometer. X-ray diffraction confirmed the formation of nanoparticles of the single-phase spinel cubic structure of NiFe2O4 of different inversion degree. The morphology of the surface showed that the particles had a spherical shape with some agglomeration. The magnetic measurements showed that coercivity, anisotropy and saturation magnetization decreased with increasing nickel content.With an increase in nickel content, an anomalous increase in the lattice parameter associated with the formation of a mixed spinel was observed. The average crystallite size in the series varied from 30 to 50nm.The results showed that the particle size, the deviation from the inverse spinel structure, and the magnetization of nickel ferrite samples increased inversely with the value of x.