Structure and Magnetoresistance of Granular Fe/Ag Alloys Produced by the Ion Cluster Beam Method

Abstract

  The structure and magnetoresistance (MR) of granular Fe/Ag alloy films produced by an ion-cluster-beam technique have been observed. Small-angle X-ray scattering and transmission electron micro-scope measurements show chemical fluctuation in the range of 15 nm and small Fe clusters about 5 nm in diameter. At 4.2 K, an MR effect is very large between 10 and 40 at%Fe, with the maximum MR value at around 20-30 at%Fe. When the Fe concentration increases from the Ag-rich side, the electrical resistivity rapidly increases at around 50 at%Fe. These features are ascribable to the geometrical and magnetic percolations of the Fe clusters. The field dependence of the MR is composed of saturation-type and non-saturation-type contributions, even at 140 kOe, indicating the contributions of large Fe clusters, small Fe atoms and molecules in the Ag-rich matrix, and Fe atoms located at the interfaces between Fe clusters and Ag matrix.