Magnetoresistance in Co–Cu Alloys Prepared by the Mechanical Alloying

Magnetoresistance (MR) has been investigated for the compacts of the Co20Cu80 mixture powders prepared by the mechanical alloying (MA) method. The crystal structure and the magnetic properties of the as-milled and the annealed samples have been examined for various milling times. The MR ratio depends on both the annealing temperature (400–550°C) and the annealing time (0–20 h). Moreover, the MR ratio depends on the milling time. The maximum MR ratio shows 6.7% (1.2 MA/m) and 7.4% (1.6 MA/m) at milling time of 50 h, after annealing at 450°C for 3 h. The substituted content of Co atom in the fcc Cu phase increases with an increase in the milling time. On the other hand, the content of Cu atom in the hcp Co phase increases with milling time, and the Co phase disappears with more than 5 h. Where, the precipitation of fcc Co crystal caused by two phase separation is observed by annealing. The magnetization of the ferromagnetic phase decreases with an increase in the milling time, and increases after annealing.