Evaluation of Fe-Ag granular materials by HRTEM and magnetogranulometry

Fe-Ag granular materials, which comprise iron clusters in a silver matrix, have been prepared by a cluster beam method, and their local structures have been investigated with high resolution transmission electron microscopy (HRTEM) and magnetogranulometry. They show that the silver matrix grows into columnar grains of 20–30 nm in diameter, in which iron clusters of about 5 nm in diameter are dispersed. The density of iron clusters increases with increasing the iron content of the films although the size of iron clusters changes little. The results of magnetogranulometry are consistent with those of TEM observations. These results enable us to account for compositional dependence of magnetoresistance: the iron clusters magnetically contact each other to attain percolation at 20–30 at.% Fe, giving rise to the maximum MR ratio.