Effects of cobalt doping on the microstructure and magnetic properties of Mn–Zn ferrites prepared by the co-precipitation method

Mn–Zn ferrite nanoparticles with various amounts of cobalt doping have been synthesized by the co-precipitation method. The structure and morphology of the nanoparticles have been characterized by X-ray diffraction and transmission electron microscopy. The effects of cobalt ions on the crystallization behavior, lattice parameters and magnetic properties of Mn–Zn ferrites have been investigated. All the Co-doped ferrite nanoparticles calcined at 1150 °C possess a simple spinel structure and have an approximately spherical shape. The lattice parameters increase almost linearly with increasing Co content. The studies of magnetic properties show that the saturation magnetization Ms strongly depends on the Co content, having a maximum Ms value of 73 emu/g at a Co content of 1.0 at%, and all the Co-doped ferrites, with the average crystallite sizes ranging from 24.5 to 27.0 nm, exhibit superparamagnetism at room temperature.