Magnetic properties of nanoparticles of Co x Fe ( 3 − x ) O 4 ( 0.05 ⩽ x ⩽ 1.6 ) prepared by combustion reaction

Nanoparticles of Co x Fe ( 3 − x ) O 4 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.