NSTI Nanotech 2009

Synthesis and Characterization of Metastable Nanocrystalline Cobalt

C. Osorio-Cantillo, O. Perales-Perez
University of Puerto Rico, US

Keywords: magnetic nanoparticles, polyol process

Abstract:

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, pseudo-cubic epsilon-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 epsilon-Co phases. Metastable epsilon-Co and hcp-Co were exclusively formed in 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 nm 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 Oe to 550 Oe depending of the presence of the different cobalt structures.
 
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