CoFe₂O₄-polypyrrole (PPy) nanocomposites: New multifunctional materials

Spinel ferrites (iron cobalt oxide) were prepared by the microemulsion method at different temperatures and sodium dodecyl sulphate (SDS) surfactant concentrations. Subsequently, a quantity of the different samples were coated with an intrinsically conducting polymer (ICP) shell of polypyrrole. The polymer shell was synthesized by a chemical route after the ferrites particle production. By combining in a single material the electrical conductivity of ICPs and the magnetic properties of nanopowder ferrites, new multifunctional materials have been developed. Different CoFe₂O₄ grain size particles were obtained ranging from 3 to 30 nm, as determined by x-ray diffraction (XRD). Particles with grain size below a critical size exhibit a superparamagnetic behaviour. These superparamagnetic particles, without and with a conducting polymer shell, were analysed by transmission electron microscopy (TEM) to find the grains' morphology and the growth evolution of the polypyrrole shell in the ferrites grains. The electrical conductivity of the nanocomposite was measured by the four points probe method, showing values of 120 ± 4 S cm^-1 at ambient temperature. The behaviour of the magnetization and the coercivity with temperature, from nearly 0 K to the ambient, were measured in a vibrating sample magnetometer (VSM).