Magnetic properties and thermal stability of graphite encapsulated cobalt nanocrystals

Small particles are of interest for magnetic study due to their range of magnetic properties with particle size and unusual magnetic properties. In this study we produced graphite encapsulated magnetic cobalt particles and measured their structural and magnetic properties both before and after annealing at 550°C for 6 hours. No large change in the structural properties (particle size, shape, and lattice parameter) was observed as a result of the annealing. There were, however, significant changes in the magnetic properties. The coercivity was found to decrease at all temperatures, especially at temperatures below 100° K. The possible reasons for this reduction in coercivity are examined, with the change in the shape of the particles appearing most likely.