K. Sumiyama et al., STRUCTURAL AND MAGNETIC EVOLUTION IN GRANULAR FE-AG ALLOYS PRODUCED BY THE CLUSTER BEAM TECHNIQUE, Materials science & engineering. B, Solid-state materials for advanced technology, 31(1-2), 1995, pp. 133-139
Using cluster beam sources, we have obtained Fe-Ag granular films, whi
ch display giant magnetoresistance, GMR, without any heat treatment. T
he experimental results of small angle X-ray scattering and high-resol
ution transmission electron microscopy indicate that a few nanometer F
e clusters are embeded in Ag matrices with 10 nm order geometrical and
chemical fluctuations. The extended X-ray absorption fine structure m
easurement indicates that the short range structure of Fe clusters is
bcc but distorted in the as-deposited state. The magnetoresistance (MR
) does not saturate at 140 kOe: conduction-electrons suffer spin-disor
der scattering even in high fields, because small Fe clusters in Ag ma
trices reveal a spin-glass character and Fe atoms at the interface a s
uperparamagnetic. After annealing above 570 K, MR saturates at high fi
elds, which is ascribed to the ferromagnetism of grown Fe clusters. Th
e concentration dependence of electrical resistivity and MR can be int
erpreted by geometrical and magnetic percolation of nanometric Fe clus
ters.