GMR effect in CuCo annealed melt-spun ribbons

A thorough microstructural and magnetic analysis has been performed on as-quenched and annealed (475 and 525 °C, 1 hour) melt-spun Cu _100-xCo _x (x = 10 and 15) granular alloys, presenting a giant magnetoresistance (GMR) effect. The annealed samples are inhomogeneous with respect to the Co-particle sizes and interparticles distances and, therefore, these particles present superparamagnetic and ferromagnetic behaviours, which determine the GMR response. The samples x = 15, treated at 525°C during 1 hour, presented the best GMR ratio (≈5% at room temperature to be the highest value approaching roughly to the saturation under an applied magnetic field of 15 KOe), with the coexistence of Co-particles with both kinds of magnetic behaviour.