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

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/m 3 . Consisting of Co 3 C and Co 2 C 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.2

CoxC nanorod magnets: Highly magnetocrystalline anisotropy with lower Curie temperature for potential applications

“…However, a knee beside the remanence has been observed at temperature ranges from 50 to 250 K. This knee originated from the decoupling of hard (Co 2 C) and soft (Co 3 C) phases that can be attributed to the differences in magnetocrystalline anisotropy K eff , magnetization M, and exchange constant A. The strong uniaxial anisotropy associated with the hard magnetic phase is capable of preventing the magnetization reversal of the soft regions [10]. These two phases are said to be exchange coupled through the inter-granular grain boundaries which appears strongly at low temperature ranges.…”

“…Any residual solvent or unreacted salts were removed by washing 3 times with ethanol. Further details are described elsewhere [10,11].…”

“…Recently a new class of hard magnetic materials based on nanocrystalline Co x C(x ¼2 or 3) have shown promise for these alternative energy applications. Cobalt carbide nanoparticles synthesized using a modified polyol process and described elsewhere [10][11][12]. These particles show a narrow size distribution, stability against oxidation, larger magnetocrystalline anisotropy, and larger coercivity.…”

Mechanical alloying preparation of fullerene-like Co3C nanoparticles with high hydrogen storage ability

“…CoeC granular films and Co 2 C thin film were fabricated via electron beam evaporation and chemical vapor deposition, respectively [22,23]. Recently, Harris et al have reported the cobalt carbide nanoparticles with a coercivity over 3 kOe at room temperature, fabricated by a direct chemical synthesis method [24]. It was reported that hcp-Co 3 C was synthesized by mechanical alloying method with precursors of cobalt and carbon powders [25].…”

Controlled synthesis and magnetic properties of hard magnetic CoxC (x=2, 3) nanocrystals

“…Co-C granular films and Co 2 C thin film were fabricated via electron beam evaporation and chemical vapor deposition [12,15], respectively. Recently, Harris et al [16] have reported the cobalt carbide nanoparticles with a coercivity over 3 kOe at room temperature, fabricated by a direct chemical synthesis method. Chemical synthesis of cobalt carbide nanostructures is interesting because of its capability to control the crystal growth in a nanometer scale.…”