Effect of the Cobalt Concentration on the Magnetic Properties of Co 1 – x Mg x Fe 2 O 4 Nanocrystals

Nanoparticles of Co 1 – x Mg x Fe 2 O 4 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 Mössbauer effect spectra, the Co 2+ 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 ×10^6 at x = 0 to 1.29 ×10^6 erg/cm 3 at x = 0.8 and drops sharply to 4 ×10^4 erg/cm 3 at x = 1.0 .