Kondo Effect and Magnetotransport Properties in Co-Cu Microwires

We studied magnetic, transport and structural properties of granular Co_x-Cu_100-x glass-coated microwires. Co-Cu microwires exhibited considerable magnetoresistance (MR) 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. Temperature dependence of magnetization measured in microwires Co_x-Cu_100-x with x ≥ 10 during a cooling regime without external magnetic field (ZFC) and in the presence of the field (FC) show considerable difference at low temperatures, attributed by us with 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 α-Co presented only in microwires with higher Co content. For low Co content (x ≤ 10%) XRD magnetic and magneto-transport measurements indicate that Co atoms and small Co clusters are distributed within the Cu crystals.