Nanoparticles of Co1 – xMgxFe2O4 with x equal to 0, 0.2, 0.4, 0.6, 0.8, and 1.0 have been synthesized. For all values of x, they are nanocrystals with a cobalt ferrite structure and an average linear size ( \(56 \pm 3)\) nm. Based on the analysis of the Mössbauer effect spectra, the Co2+ ions were shown to occupy only octahedral positions at all values of x. The experimentally obtained dependence of the nanoparticles magnetization on x corresponds to the dependence calculated using the Mössbauer effect data, except for the sample with \(x = 1.0\) . The effective magnetic anisotropy constant estimated for 0 K from the analysis of the coercive force temperature dependences decreases from \(5.27 \times {{10}^{6}}\) at \(x = 0\) to \(1.29 \times {{10}^{6}}\) erg/cm3 at \(x = 0.8\) and drops sharply to \(4 \times {{10}^{4}}\) erg/cm3 at \(x = 1.0\) .
