GIANT MAGNETORESISTANCE IN SPUTTERED (CO70FE30)XAG1-X HETEROGENEOUS ALLOYS

We report the structural, magnetic and transport properties of (Co70Fe 30)xAg1-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 pha se segregation and grain growth, resulting in the formation of small a nd compact Co70Fe30 precipitates. The resulting evolution of the magne tic properties has been investigated by SQUID magnetometry, Mossbauer spectroscopy and ferromagnetic resonance. The largest magnetoresistanc e amplitudes at room temperature have been obtained for a magnetic con centration x of around 36 at.% in both as-deposited and annealed sampl es. Amplitudes DELTAR/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 DELTAR/R(H = 2 T) = 7 5%).