STRUCTURAL DIFFERENCE BETWEEN FE CU AND FE/AG GRANULAR FILMS PRODUCEDBY A CLUSTER BEAM METHOD/

Fe/Cu and Fe/Ag granular alloy films have been produced using a cluste r-beam source: Fe clusters from the nozzle of a high temperature cruci ble are directly dispersed in Cu and Ag matrices obtained by simultane ous vapor deposition. They reveal a giant magnetoresistance effect wit hout any heat treatment. High-resolution transmission electron microsc ope observations indicate the presence of nanometric Fe clusters toget her with ten-nanometer sized geometrical an chemical fluctuations in t hese films. Extended X-ray absorption fine structure experiments indic ate that the local structure around Fe atoms is fcc for Fe concentrati ons less than 22 at.% and bcc for more than 35 at.% Fe in Cu matrices, while the structure of the Fe cluster is distorted bcc-like even for low Fe content down to 12 at.% in Ag matrices. These results suggest t hat small Fe clusters can diffuse on the substrate to form larger clus ters. Small Fe clusters also intermix with Cu and Ag matrices to give rise to nanoscale heterogeneity. However, since the immiscibility of F e with Ag is more remarkable than that with Cu, aggregation of Fe clus ters is accelerated in Ag matrices.