Magnetic properties of fine cobalt particles prepared by metal atom reduction

Abstract

Ultrafine particles of cobalt were prepared under argon by reduction of cobalt halide solutions in diglyme ether with metallic lithium and a naphthalene catalyst. The fine particles had a particle diameter in the range 50–1200 Å. The size was dependent on the reaction temperature. X-ray diffraction showed crystalline particles of α-Co and CoO. Because the ratio of the metal core to oxidized shell decreases with particle size, the smaller particles displayed much lower magnetization and higher coercivity at low temperature. The anisotropy constant K changes slightly with particle size and has a value close to the bulk value.