Synthesis and magneto-structural study of CoxFe3-xO4

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 CoxFe3-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 CoxFe3-xO4 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 CoxFe3-xO4 powders shows that an increase of the cobalt contain yields a steadily decrease in the maximum magnetization. (C) 2005 Elsevier B.V. All rights reserved.