Relaxation of magnetoresistance and magnetization in granular Cu90Co10 obtained from rapidly quenched ribbons

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Abstract
Bulk granular Cu90Co10 systems displaying a negative giant magnetoresistance (GMR) were produced by submitting melt‐spun ribbons to conventional annealing and dc joule heating in order to induce diverse microstructures. Room‐temperature GMR values up to 9% at 20 kOe were found in samples produced using both kinds of thermal treatments. An evolution from a superparamagnetic towards a ferromagnetic behavior has been observed in samples submitted to different heat treatments. A long‐time, nearly logarithmic relaxation of the magnetic remanence has been measured after fast removal of a magnetic field of 10 kOe. The progressive randomization of the magnetic moments also gives rise to a corresponding increase in the zero‐field electrical resistance.