Determination of size and interface hyperfine field of Co nanosized precipitates in Ag by Mössbauer spectroscopy

Abstract

We induced Co to form inclusions in Ag by ion implantation of Co into Ag and by coevaporation of both elements in a MBE system. Mössbauer spectroscopy at 4.2 K reveals the hyperfine fields present in the bulk and at the interface of the precipitates. By post-implanting the 57Co activity into the coevaporated samples, we strongly enhanced this interface population, which facilitates the determination of the associated magnetic hyperfine field. The dependence of the precipitate size on the Co concentration and annealing treatment is monitored. We propose a simple model which allows to estimate the precipitate size in the case of preferential interface population.

Theoretical study of hyperfine and local magnetic properties of Co and Fe clusters in fcc Ag hosts

“…We note that this reflects the fact that the majority band is almost full and the minority band is almost empty, so the local moment is saturated. Concerning the HF values for this type of granular systems, the experimental results found in the literature 6,7 suggest values of around Ϫ31 T for Fe atoms inside the cluster and values in the range between Ϫ25.3 and Ϫ29.0 T for atoms at their surfaces. They also suggest that the HF should be more intense for larger clusters.…”

“…In this direction, different measurements of hyperfine properties of Co-Ag granular systems have recently been presented in the literature. [5][6][7][8][9][10][11] The advantage of the use of hyperfine interactions techniques is that they can provide information about small clusters and local environments, which other techniques are usually not able to study. The structural evolution due to annealing in sputtered Co/Ag multilayers was analyzed by the distributions of hyperfine fields, obtained using nuclear magnetic resonance ͑NMR͒ in Ref.…”

“…Mössbauer spectroscopy ͑MS͒ was used in Refs. [5][6][7] to study the formation of Co clusters in fcc Ag, and samples produced by different techniques ͑coevaporation and ion im-plantation͒ were analyzed. The observed spectra suggest the presence of Fe atoms as isolated impurities, as dimmers and inside or at the surface of Co clusters.…”

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

“…We have however tried this with the 57 Co probe, taking advantage of the relatively large diffusivity of Co in Ag, compared to that of Co in Co. In a study that was mainly aimed at a determination of the magnetic hyperfine field associated with interface Co atoms, 30 we created Co nanoparticles in a Ag matrix by coevaporating both species and postimplanting the samples with probe atoms. At 4.2 K, the spectral contribution of these probes which had taken up an interface site lies between 30 and 40 % after room temperature ͑RT͒ preparation and between 45 and 65 % after 400°C annealing.…”

“…%, corresponding to particle diameters after RT preparation between 7 and 16 nm, as deduced from the probe atom populations, 30 and of only 4 nm for a 15 at. % sample, as we could deduce from fitting the magnetization to a Langevin function.…”