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

Magnetic iron oxide nanoparticles/ C and alpha-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 degrees C under N-2 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 degrees C. Increasing the annealing temperature to higher temperature ( 1000 degrees C) could result in the partial reduction of iron oxide to alpha-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 alpha-Fe/ iron oxide nanoparticles make the as-obtained composites useful for various magnetic applications. (C) 2007 Elsevier B.V. All rights reserved.