Evolution of the microstructure and magnetic properties of a cobalt-silicon-based alloy in the early stages of mechanical milling

The early stages in the mechanical alloying of amount fractions x = 40 % cobalt (Co) and x = 60 % silicon (Si) powders were investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and vibrating-sample magnetometry (VSM). After 2–8 h of ball-milling, the characteristic XRD peaks of the face-centered-cubic (fcc) Si and hexagonal close-packed (hcp) Co phases remained sharp without a cobalt-silicide phase. As the milling progressed, the particle size observed by SEM tended to reduce, being accompanied by smoother edges and a narrow size distribution. On the DTA curves, between 200 °C and 1200 °C, exothermic peaks indicated a ferromagnetic-to-paramagnetic transition, whereas endothermic peaks corresponded to the lattice recovery, the transition from a hcp to a fcc Co and melting. The longest milling of up to 8 h significantly increased the magnetic squareness and the coercive field