Synthesis and characterization of metastable nanocrystalline cobalt

Applications of elemental cobalt are consequence of its phase-dependent magnetic properties; the anisotropic high-coercivity hcp-Co phase is preferred for permanent magnet applications, while the more symmetric low coercivity fcc- and pseudocubic ε-Co can be used in soft magnetic applications involving power electronics and magnetic write heads. The present work addresses the synthesis and characterization of nanocrystalline cobalt particles produced through a modified polyol-based approach conducive to the formation of fcc-, hcp-, or ε-Co phases. Metastable ε-Co and hcp-Co were exclusively formed in the presence of trimethylene glycol. In turn, fcc-Co or mixture of fcc/hcp-Co phases were produced in tetraethylene glycol. The average crystallite size in all cases ranged between 10 and 13 nm. Magnetic measurements confirmed the strong influence of synthesis conditions on crystal structure and hence on magnetic properties of nanocrystalline cobalt. The coercivity of the products varied from 338 to 550 Oe depending on the presence of the different cobalt structures.