STRUCTURAL EVOLUTION OF AG-CO AND AG-NI ALLOYS STUDIED BY ANOMALOUS SMALL-ANGLE X-RAY-SCATTERING

The structural evolution of co-sputtered Ag-20 (and 35) at.% Co and Ag -20 (and 35) at.% Ni was studied by anomalous small-angle X-ray scatte ring in the as-deposited state and after different anneals for 10 min at 573, 623 and 723 K. Anomalous scattering was used to separate the p art of the scattering signal due to the transition metal particles fro m the signal of other heterogeneities. Strong segregation, involving a bout two-thirds of the Co (or Ni) atoms, already exists for the as-dep osited state. After a 573 K anneal, the phases (Ag matrix and Co or Ni well defined particles) have almost reached equilibrium, i.e. complet e immiscibility. Most of the magnetic particles are three dimensional with an average radius of 5-25 Angstrom and the average distance betwe en the particles varies from 17 to 110 Angstrom, depending on the magn etic element and its concentration, and on the annealing conditions. T he size distribution does not correspond to that of usual coarsening, but becomes broader after extended annealing. This is probably due to heterogeneous precipitation at grain boundaries of the Ag matrix.