Abstract
Iron clusters have been dispersed in silver matrices using cluster beam (CB) sources without any heat treatment. Their structure and morphology have been studied by comparison with those of the sputter-deposited Fe-Ag alloys using small angle x-ray scattering, high resolution transmission electron microscopy and extended x-ray absorption fine structure measurements. In the granular alloys made by CB, bcc Fe clusters of a few nanometers dimension are detected, together with ten-nanometer scale geometrical and chemical fluctuations. In the sputter-deposited alloys, the Fe atoms are rather well mixed with the Ag atoms in the as-deposited state, and fcc Fe clusters are first formed and transform to larger bcc particles with increasing annealing temperature. The field-dependence of the magnetoresistance is well correlated with the growth mode of the Fe clusters in the granular alloys.