Evidence for Kondo Effect in Au80Co20 Ribbons

A minimum in resistivity as a function of temperature for an as-quenched Au80Co20 ribbon prepared by melt-spinning using a wheel surface speed of 20 m s^{-1} is found at 25 K. No resistivity minimum is found for an as-quenched ribbon using a wheel surface speed of 60 m s^{-1}, however, upon heat treatment of this ribbon a resistivity minimum is recovered. The temperature of the minimum decreases with increasing total time of heat treatment. These observations are interpretted as evidence for the microstructural control of the Kondo effect typically found in dilute magnetic alloys in a giant magnetoresistance granular material.