Structure and giant magnetoresistance in electrodeposited granular Cu–Co films

Abstract Cu–Co alloy films have been electrodeposited galvanostatically from a single sulphate bath. XRD reveals the as-deposited films to be single phasic metastable FCC alloy of Cu and Co with a grain size of 5–20 nm. Phase separation on annealing forms fine Co granules at the core of Co-rich shells. The grain size grows to 40–60 nm after annealing at 400°C for 1 h. A total phase separation into Cu (FCC) and Co (FCC) is observed after annealing at 700°C. Maximum room-temperature magnetoresistance (MR) of 4% at a magnetic field of 10 kOe was observed for film annealed at 450°C for 1 h. A MR ratio of 7.8% was observed at 20 K in a magnetic field of 3 kOe. The MR was observed to increase with film thickness. Coexistence of typical superparamagnetic and ferromagnetic features is observed in the room-temperature magnetization curves of as-deposited and 400°C annealed films.