Abstract
Nanocrystalline b.c.c. cobalt powder has been prepared using a combination technique of mechanical alloying and leaching aluminum in basic solution. The structure and magnetic properties of the as-milled and the leached alloys were examined by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and magnetization measurements. Even after removing most of the aluminum atoms by leaching, the specimen topotactically keeps the b.c.c. structure. The b.c.c. cobalt is ferromagnetic is stable below 430 K and transforms into the ferromagnetic f.c.c. cobalt at higher temperatures. The magnetic moment of the cobalt atom is smaller in the b.c.c. phase than in the f.c.c. phase.