Giant magnetoresistance in sputtered (Co70Fe30)xAg1-xheterogeneous alloys

We report the structural, magnetic and transport properties of (Co 70 Fe 30 ) x Ag 1-x heterogeneous alloys, with x varying between 27 and 47 at.%. The samples were prepared by DC triode sputtering at room temperature (RT) and liquid-nitrogen temperature. Annealing processes lead to phase segregation and grain growth, resulting in the formation of small and compact Co 70 Fe 30 precipitates. The resulting evolution of the magnetic properties has been investigated by SQUID magnetometry, Mossbauer spectroscopy and ferromagnetic resonance. The largest magnetoresistance amplitudes at room temperature have been obtained for a magnetic concentration x of around 36 at.% in both as-deposited and annealed samples. Amplitudes Delta R/R(H=0) of 15% in the as-deposited samples and 21% in samples annealed at 600 K for 10 min have been observed at RT. At 4 K these amplitudes reach 43% (equivalent to Delta R/R(H=2 T)=75%).