High coercivity cobalt carbide nanoparticles processed via polyol reaction: a new permanent magnet material

Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers high product yields in a cost effective single-step process. Particles are shown to be acicular in morphology and typically assembled as clusters with room temperature coercivities greater than 3.4 kOe and maximum energy products greater than 20 kJ m−3. Consisting of Co3C and Co2C phases, the ratio of phase volume, particle size and particle morphology all play important roles in determining permanent magnet properties. Further, the acicular particle shape provides an enhancement to the coercivity via dipolar anisotropy energy as well as offering potential for particle alignment in nanocomposite cores. While Curie temperatures are near 510 K at temperatures approaching 700 K the carbide powders experience an irreversible dissociation to metallic cobalt and carbon thus limiting operational temperatures to near room temperature. These findings warrant more extensive investigation of this and other magnetic carbide systems in which particle size, chemistry and morphology are optimized.