Magnetic properties of nanoparticles of CoxFe(3-x)O4 (0.05≤x≤1.6) prepared by combustion reaction

Nanoparticles of CoxFe(3-x)O4 with x ranging from 0.05 to 1.6 were synthesized by a combustion reaction method using iron nitrate, cobalt nitrate, and urea as fuel. X-ray diffraction patterns of all systems showed broad peaks consistent with the cubic inverse spinel structure of cobalt ferrite. The absence of extra reflections in the diffraction patterns of as-prepared materials, with x=0.6, 0.8, and 1.0, demonstrates the phase purity. Magnetization measurements show that the saturation magnetization (M-s), coercivity (H-c), and remanent magnetization (M-r) depend on the molar cobalt concentration and the temperature as well. At 4 K, the reduced remanence, M-r/M-s, are equal to 0.66 and 0.63 for x=0.8 and 1.0, respectively, indicating that cubic-type magnetic anisotropy is significant in these nanoparticles. These observations are discussed in terms of a model in which it is assumed that each crystallite consists of a ferromagnetic core surrounded by a magnetically disordered shell. (c) 2007 American Institute of Physics.