Synthesis and magnetic properties of iron oxide nanoparticles/C and α-Fe/iron oxide nanoparticles/C composites

Magnetic iron oxide nanoparticles/C and α-Fe/iron oxide nanoparticles/C composites were synthesized through the formation of polymer gel with highly dispersed magnetic iron oxide nanoparticles in hydrothermal system, followed by carbonizing the gel at 400 and 1000 °C under N2 atmosphere, respectively. The phase component, structure and magnetic properties of these magnetic composites were characterized by X-ray diffraction analysis, transmission electron microscopy and magnetic measurements. Spherical iron oxide nanoparticles with variable average diameter (12.5–25 nm) and narrow size distribution were homogeneously embedded in amorphous carbon matrix when the gel was annealed at 400 °C. Increasing the annealing temperature to higher temperature (1000 °C) could result in the partial reduction of iron oxide to α-Fe through nanoscale carbothermic reaction and the graphitization of amorphous carbon matrix as well as the change of superparamagnetism into ferromagnetism. The magnetic properties of iron oxide and α-Fe/iron oxide nanoparticles make the as-obtained composites useful for various magnetic applications.