Growth and lattice dynamics of Co nanoparticles embedded in Ag: A combined molecular-dynamics simulation and Mossbauer study

We use Mossbauer spectroscopy in combination with atomic scale modeling in order to gather a comprehensive understanding of the growth and the dynamics of cobalt nanoprecipitates in silver. The modeling makes use of classical molecular dynamics in the canonical ensemble by means of the Rahman-Parinello technique. Atomic interactions are governed by an embedded atom model, which is validated for the static Co-Ag interaction by means of a comparison with extended x-ray absorption fine structure measurements and for the dynamical interaction with Mossbauer spectroscopy data. This allows us to identify the cluster size dependent atomic arrangements at the cluster-matrix interface, where strong relaxation takes place. A detailed analysis of the Mossbauer spectra taken at two temperatures after annealing at different temperatures allows us not only to characterize the cluster size dependence of magnetic properties, but also to evidence a possible Ostwald ripening growth mechanism. The mean and interface Debye temperatures are deduced from the Mossbauer spectra and found quite consistent with the model predictions. On this basis, the atomic scale modeling allows us to identify detail of atomic vibrational properties as a function of distance from the cluster center and a discontinuity of the vibration amplitudes at the precipitate-matrix interface is evidenced.