Giant magnetoresistance in mechanically alloyed Ag-Cu-Fe alloys

(Ag_0.6Cu_0.4)_l-xFe_x alloys with x = 0.10, 0.15, 0.20, and 0.25 were prepared by mechanically alloying mixtures of elemental Ag, Cu, and Fe powders. A metastable fcc solid solution containing a nanosized distribution of magnetic Fe-rich particles was formed for all compositions. The alloys were characterized in the as-mechanically alloyed (as-MA) condition and after various annealing treatments by X-ray diffraction, magnetic balance measurements, and magnetoresistance measurements. The as-MA alloys show a giant magnetoresistance (GMR-) effect which increases with decreasing temperature. For x = 0.15, the GMR effect reaches a value Δρ/ρ≈0.2 at a temperature of 4 K and afield of 10 T. The magnetic particles coarsen on annealing above 473 K to produce ferromagnetic particles. Annealing for 30 minutes at 573 K increases the GMR effect at low magnetic fields. These effects are explained in terms of the proportion of superparamagnetic to ferromagnetic particles and the total particle interfacial area per unit volume.