Magnetic and transport properties of Co-Cu microwires with granular structure

Magnetic, transport and structural properties of granular Co-x-Cu100-x (5 < x < 40 at.%) glass-coated microwires were studied. Co-Cu microwires exhibited giant magnetoresistance (GMR) effect. For x=5% we observed the resistivity minimum at 40 K associated with the Kondo effect. For x > 10 partial evidences of granular structure have been observed. For x >= 30 anisotropic contribution to GMR has been observed giving rise to nonmonotonic dependence of GMR on the field. Temperature dependence of magnetization measured during a cooling regime without external magnetic field and in the presence of the field shows considerable difference at low temperatures, being attributed to the presence of small Co grains embedded in the Cu matrix. By X-ray diffraction we found, that the structure of the metallic nucleus is granular consisting of two phases: fcc Cu appearing in all the samples and fcc alpha-Co presented only in microwires with higher Co content. For low Co content (x <= 10%) X-ray diffraction technique indicates that Co atoms are distributed within the Cu crystals. The quantity and the crystallite size of the formed phases strongly depend on the geometry of the microwire. The structure, magnetic and transport propertieswere affected by the glass coating inducing the internal stresses and affecting the quenching rate. (C) 2013 Elsevier B.V. All rights reserved.