Microstructure and magnetic properties of melt-spun Cu0.95Co0.05 granular alloy

We have synthesized Cu0.95Co0.05 granular alloy in ribbon form and X-ray diffraction showed that the ribbon was polycrystalline (that means it is granular), face-centered-cubic (fcc) bulk Cu structured and (2 0 0) textured. The tiny amount of Co or Co rich Cu phases has been identified from the well resolved shoulders accompanied with diffraction peaks of fcc Cu. Scanning electron micrographs showed the formation of grains or particles of two prominent sizes. Upon annealing, the number density of bigger plate like grains decreases and that of the smaller grains increases. The magnetic measurement showed that the ribbon was superparamagnetic at room temperature, but ferromagnetic at 5 K. The ribbon showed giant magnetoresistance (GMR) effect, which was 4% for as-quenched sample and enhanced to 27% upon annealing at 550 °C. This enhancement is attributed to the increment of the number density of Co-rich Cu particles upon annealing.