Phase composition and magnetic properties of Ni$_{1-x}$Co$_x$Fe$_2$O$_4$ nanocrystals with spinel structure, synthesized by Co-precipiation

Nanopowders of nickel ferrite doped with cobalt were synthesized by co-precipitation using a 3 % KOH solution as a precipitant. The effects of different annealing regimes on the composition and particle size of Ni$_{1-x}$Co$_x$Fe$_2$O$_4$ were studied. It was established that with annealing at t = 1000$^\circ$ C for 2 h single-phase products were formed with a crystallite size of 30–50 nm. The saturation magnetization and the coercive force increased as the content of the dopant increased from 50.3 emu/g and 51.94 Oe for Co$_x$Fe$_2$O$_4$ to 80.45 emu/g and 848.32 Oe for CoFe$_2$O$_4$.