Effect of Cobalt Concentration on the Magnetic Properties of the Co1 – xMgxFe2O4 Nanocrystals

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 ± 3) nm. Based on the analysis of the Mossbauer 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 Mossbauer 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 × 106 at x = 0 to 1.29 × 106 erg/cm3 at x = 0.8 and drops sharply to 4 × 104 erg/cm3 at x = 1.0.