Structure, magnetic properties and giant magnetoresistance in melt-spun Cu-Co ribbons

Authors report a comprehensive investigation of structure, magnetization and transport properties of as-quenched and annealed Co _xCul-x(0< x < 0.22) granular alloys prepared by melt-spinning. Using X-ray diffraction, DCS measurements, and magnetic characterization, we have uncovered a Co phase separation process which results in the variation of magnetic and transport properties of Co-Cu heterogeneous alloys. In the Co composition range (0 < x < 0.15) the maximum GMR was observed for CoCu samples annealed at 450°C for 30 min, where Co particle diameters are in the range of 3.5 to 4.5 nm. The variation of magnetic and transport properties with the concentration and size of precipitated Co clusters is discussed, and is consistent with the prediction of the two-channel model, in which spin-dependent scattering is dominated by the cluster-matrix interfaces. The reduction of GMR in high Co concentration is attributed to the appearance of magnetic coupling among magnetic particles. In contrast, very small particles tend to behave superparamagnetic, resulting in the reduction of the ratio of spin-dependent scattering to spin-independent scattering potentials, and thus in the reduction of the GMR effect.