Magnetotransport and magnetic properties of mechanically alloyed CoxCu100-x

Co-Cu binary alloys, whose Co concentrations range from 10 to 30 at.%, are produced by mechanical alloying. The structure, magnetoresistance (MR), and magnetism have been investigated for the as-milled and annealed alloys. After milling for 50 h, a supersaturated solid solution of fcc-CoCu is formed at Co concentrations of 10 to 30 at.%. The CoxCu100-x (x = 10-30) alloys annealed at 700 degrees C for 1 h separate into two phases of fcc-Co and fcc-Cu. The maximum MR ratio, under 15 kOe at room temperature, is 6.4% for the sample with x = 20 annealed at 450 degrees C for 1 h. The samples annealed at temperatures less than 450 degrees C exhibit high MR ratio at x = 25. The magnetism of the sample with x = 20, which shows a maximum MR ratio, exhibits superparamagnetic behavior, but a slight ferromagnetic behavior have also been observed. Co-Cu alloys produced by mechanical alloying have a wide distribution of Co particle size with blocking temperature from low temperature to room temperature.