This paper reports a thorough microstructural and magnetic analysis performed on as-quenched and annealed melt-spun ${\mathrm{Co}}_x{\mathrm{Cu}}_{100-x}$ granular alloys presenting giant magnetoresistance. The use of three different techniques has been necessary to follow the evolution of the Co atoms with the thermal treatment. X-ray diffraction (XRD) detects the fraction of the Co atoms which are arranged in nanometric clusters. From the analysis of the hysteresis loops we have identified three different Co arrangements, each one with a different magnetic response: Co superparamagnetic nanoclusters, a Co-rich ferromagnetic phase, previously detected by XRD, and Co atoms diluted into the Cu matrix with no magnetic contribution. Finally, by means of the extended x-ray absorption fine structure spectroscopic technique performed on the Co K edge, we have analyzed the local configuration of the Co atoms, in particular, at the interfaces between the magnetic nanoclusters and the Cu matrix. Using the information gathered with these techniques, the microstructural evolution has been correlated to the giant magnetoresistance response of the CoCu system.

• Received 5 November 2002

DOI:https://doi.org/10.1103/PhysRevB.67.224415