Giant magnetoresistive properties in granular transition metals

The giant magnetoresistance (GMR) in granular Co-Ag, Co-Cu, and Fe-Ag systems, as well as in the metastable alloy state, is studied. The absolute values of the resistivity at zero field (ρ₀), the magnetic resistivity (ρ_m), and GMR are determined. The resistivity of an alloy is found to be significantly larger than that of a granular solid. As the composition (x) of Co or Fe is increased, ρ_m shows a broad maximum at x=20 to 30%. Among the three systems, Co-Ag has the smallest ρ(0), the largest ρ _m, and hence the largest GMR. Both ρ(0) and ρ_m at 5 K in all three systems show a similar dependence on the annealing temperature (T_A). They decrease with increasing T _A, having the largest values in the as-deposited samples, regardless of the sample being alloy or granular. Because ρ₀ and ρ_m decrease with T_A at different rates, there may or may not be a peak in the GMR at certain value of T _A