Bulk metastable cobalt in fcc crystal structure

Bulk metastable pure cobalt was fabricated by a simple sintering route with micrometer-sized Co particles as raw materials. The as-prepared bulk Co is composed of dominant metastable face-centered cubic (fcc) phase and a trace of hexagonal close-packed (hcp) phase at room temperature. The crystal structures and magnetic properties of the metastable bulk are very sensitive to external stresses. Obvious fcc-to-hcp phase transformation occurred under tensile loading, which was accompanied by significant increase of the coercivity and remanence. It is believed that the interface energy plays a key role in hindering the fcc-to-hcp allotropic transition, leading to the existence of metastable bulk Co with the high-temperature fcc structure at room temperature.