Giant magnetoresistance in mechanically alloyed Ag-Cu-Fe alloys

(Ag0.6Cu0.4)(1-x)Fe-x alloys with x =: 0.10, 0.15, 0.20, and 0.25 were prep ared by mechanically alloying mixtures of elemental Ag, Cu, and Fe powders. A metastable fee solid solution containing a nanosized distribution of mag netic Fe-rich particles was formed for all compositions. The alloys were ch aracterized in the as-mechanically alloyed (as-MA) condition and after vari ous annealing treatments by X-ray diffraction, magnetic balance measurement s, and magnetoresistance measurements. The as-MA alloys show a giant magnet oresistance (GMR-) effect which increases with decreasing temperature. For x = 0.15, the GMR effect reaches a value Delta rho/rho approximate to 0.2 a t a temperature of 4 K and afield of 10 T. The magnetic particles coarsen o n annealing above 473K to produce ferromagnetic particles. Annealing for 30 minutes at 573K increases the GMR effect at low magnetic fields. These eff ects are explained in terms of the proportion of superparamagnetic to ferro magnetic particles and the total particle interfacial area per unit volume. (C) 1998 Acta Metallurgica Inc.