Heterogeneous CoxAg1−x and NixAg1−x alloys have giant
magnetoresistance properties. Such alloys, with atomic concentrations x = 0.20 and 0.37,
were studied by transmission X-ray Absorption Spectroscopy at the Co or Ni K-edge after
in situ thermal annealing. For alloys as-deposited and annealed at 200 °C,
Extended X-ray Absorption Fine Structure analysis displays both Co-Co (Ni-Ni) bonds related
to Co (Ni) atoms agglomerated in magnetic particles and Co-Ag (Ni-Ag) bonds related to Co
(Ni) atoms in substitutional sites in the Ag matrix. At the same alloy concentration, the
miscibility in the Ag matrix is found larger for Ni than for Co. After annealing around
250 °C, the marked decrease of the Ag neighbour peak corresponds to a diffusion of
magnetic atoms outside the Ag matrix. The Co-Co coordination number increases regularly with
annealing temperatures up to 450 °C reflecting a progressive expansion of Co
particles. On the contrary, for Ni alloys, no further particle expansion has been observed
in the same annealing range. This different behaviour may be linked both to the difference
between the as-deposited structural states and to the Co/Ag and Ni/Ag interfaces energies.
Using a simple model, evolution of the mean particle size has been estimated as a function
of annealing.