Abstract
CoxCu100-x (x= 10-30) alloys were prepared by mechanically milling mixtures of elemental Co and Cu powders. The structure, magnetoresistance (MR), and magnetic properties were examined for the as-milled and annealed alloys. The hcp-Co phase disappeared after milling for 50 h, and the Co atoms were dissolved in the fcc-Cu phase. The MR ratio showed a maximum of 6.7% (15 kOe, room temperature) at a Co concentration of x = 20. For higher Co concentrations, the annealing temperature needed to produce high magnetoresistance was lower and the annealing time was shorter. The CoxCu100-x alloy with x=20 showing a maximum MR exhibited superparamagnetic behavior, but had a slight ferromagnetic state. The average grain size of Co particles, estimated from the temperature dependence of magnetization, was 5-7 nm.
