Observation of resistivity minimum at low temperature in CoxCu1-x (x ∼ 0.17-0.76) nanostructured granular alloys

Electrical resistivity of nanostructured granular alloys CoxCu1-x(x similar to 0.01-0.76) prepared by the chemical reduction method is investigated in the temperature range 2-300 K. The samples with a low cobalt content of x <= 0.1 show a metallic resistivity behavior. For samples with a higher cobalt content, x >= 0.17, the resistivity shows a minimum. The minimum becomes more pronounced as Co content (x) increases and also as the temperature of minimum resistivity, T-min, increases with x. The resistivity minimum is obtained in this magnetic alloy system even for a cobalt concentration as high as similar to 76%. Application of an external magnetic field has a negligible effect on the resistivity behavior. Detailed analysis suggests that the low -temperature upturn in resistivity most probably arises due to elastic electron-electron interaction (the quantum -interference effect). Magnetic measurements at 4 K on the same samples show the absence of long-range magnetic interaction and evidence of increasing magnetic disorder as x increases beyond similar to 10%. Combining the results of the two types of measurements, a model of formation of these alloy particles involving random clusters of Co atoms within the Cu matrix has been proposed.