ON THE ROLE OF CU AND NB IN THE FORMATION OF NANOCRYSTALS IN AMORPHOUS FE73.5NB3CU1SI13.5B9

Extended x-ray absorption fine structure analysis of amorphous and par tially crystallized samples of the soft magnetic alloy Fe73.5Nb3Cu1Si1 3.5B9 reveals that, even before heat treatment, a portion of the Cu is present in the form of tiny, close packed clusters. Analysis of the N b-free alloy Fe76.5Cu1Si13.5B9 shows that the Cu clusters are not pres ent in the quenched ribbons, but that fcc Cu precipitates form during heat treatment. Results suggest that the Cu clusters act to catalyze n ucleation of Fe-rich nanocrystals, but that these clusters are formed on a finer scale when Nb is added to the alloy, perhaps because it hel ps to lower the solubility of Cu in the amorphous phase.