GIANT MAGNETORESISTIVE PROPERTIES IN GRANULAR TRANSITION-METALS

We have studied the giant magnetoresistance (GMR) in granular Co-Ag, Co-Cu, and Fe-Ag systems, as well as in the metastable alloy state. The absolute values of the resistivity at zero field (rho0), the magnetic resistivity (rho(m)), and GMR have been 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, rho(m) shows a broad maximum at x = 20 to 30 %. Among the three systems, Co-Ag has the smallest rho(0), the largest rho(m), hence the largest GMR. Both rho(0) and rho(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 rho(0) and rho(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).