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

TL;DR

This paper reports a cost-effective method to produce cobalt carbide nanoparticles with high coercivity and energy product, suitable for permanent magnet applications, though limited by thermal stability.

Contribution

Introduces a polyol reduction process for cobalt carbide nanoparticles with high coercivity and potential for magnetic alignment, advancing permanent magnet material development.

Findings

Particles exhibit coercivities >4 kOe and energy products >20 KJ/m3.

Acicular shape enhances coercivity through dipolar anisotropy.

Thermal stability is limited near 510K due to dissociation.

Abstract

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 4 kOe and maximum energy products greater than 20 KJ/m3. 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 510K 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.