MAGNETIC AC SUSCEPTIBILITY STUDY OF THE COBALT SEGREGATION PROCESS INMELT-SPUN CU-CO ALLOYS

Temperature and frequency-dependent AC susceptibility has been used to characterize Cu90Co10 melt-spun ribbons, about 15 mu m thick, in orde r to see to what extent this technique yields information about the se gregation of cobalt in this alloy. The interpretation of the results i ncludes, as a prerequisite, a transmission electron microscopy (TEM) c haracterization and makes use of previous field-dependent magnetizatio n data on the same samples. Due to their different dynamical magnetic properties, the large intergrain precipitates, the small intragrain ag gregates and the remaining Cu-Co solid solution, previously detected i n these alloys, are independently observed by AC susceptibility as fer romagnetic, superparamagnetic and spin-glass species. Contrary to othe r, mostly local, microstructural characterization techniques of use wi th nanostructured materials, the AC susceptibility yields information about the whole sample. Furthermore, unlike the measurement of the tem perature-dependent magnetization which is the magnetic technique mostl y used until now, the results are basically independent of the thermal history. The correlation between microstructure and magnetic properti es is illustrated by a scheme which includes magnetization, AC suscept ibility and TEM data. (C) 1998 Elsevier Science B.V. All rights reserv ed.