Laser synthesis and magnetism of amorphous iron and cobalt carbide nanoparticles with carbon onion

Amorphous iron or cobalt carbide nanoparticles with a carbon onion structure were produced using a pulsed laser ablation of metallocene powders at room temperature. While they are ferromagnetic at room temperature, they exhibit a drastic change in magnetic spin moments at 20-30 K. These magnetic properties are ascribed to a considerable magnetic contribution of superparamagnetism for the amorphous iron or cobalt carbide nanoparticles with a carbon onion and the origin of the magnetic properties is discussed.