Synthesis and magneto-structural study of Co_xFe _3-xO₄ nanoparticles

The Co²⁺ ion in an octahedral site of the cubic spinel structure has a highly anisotropic character. The electric crystal field produces a degenerate ground state with a orbital magnetic momentum fixed parallel to a 〈1 1 1〉 trigonal axis, and the spin-orbit interaction tends to align the spin magnetic moment parallel to this trigonal axis giving high anisotropy. Then, the use of Co_xFe_3-xO₄ system allows the tailoring of the magnetic properties by changing the cobalt content, which can be very useful in magnetic fluids, magnetic latex and free rotors applications. In this work Co_xFe_3-xO ₄ nanoparticles over a compositional range 0.0<x<1.0 were synthesized by chemical co-precipitation from iron and cobalt salts using ammonium hydroxide as precipitating agent. The powders were characterized by X-ray diffraction, transmission electronic microscopy and vibrating sample magnetometry. Nanoparticles with a size smaller than 15 nm with a narrow particle distribution size were obtained. X-ray diffraction confirmed the formation of a unique phase. The magnetic behavior of Co_xFe _3-xO₄ powders shows that an increase of the cobalt contain yields a steadily decrease in the maximum magnetization.