The influence of relative content of a metal component in a dielectric matrix on the formation and dimensions of cobalt nanocrystallites in Co$_{x}$(MgF$_{2}$)$_{100-x}$ film composites

The influence of relative content of a metal component on the phase composition and substructure of Co$_{x}$(MgF$_{2}$)$_{100-x}$ in a wide range of $x$ = 16–63 at % is studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy. The layers of nanocomposite with a micron thickness have been obtained by the ion-beam sputtering of the target in the argon environment. The results reveal that the relative metal cobalt content in the MgF$_2$ dielectric matrix strongly affects the phase composition and substructure of nanocomposites. With a lower content of cobalt, it is in the amorphous state in the form of clusters in the Mg$F_2$ nanocrystalline matrix. An increase of cobalt content to $x$ = 29 at % on a sitall substrate and to $x$ = 42 at % on a glass substrate in the X-ray amorphous MgF$_2$ dielectric matrix leads to the formation of cobalt nanocrystals with a hexagonal crystallographic system, whose sizes are on the order of 10 nm. These are predominately oriented in the basis plane of the (001) hexagonal lattice of $\alpha$-Со. A further increase of cobalt content to $c$ = 59 at % enlarges the $\alpha$-Со nanocrystals to $\sim$20 nm with retaining the same orientation. In accordance with a fine structure analysis of XPS spectra of Со $2p$ and О $1s$, cobalt is strongly oxidized on the surface of all the composites; only on the surface of samples with a low content of Co is X-ray amorphous cobalt found in a metallic state along with cobalt oxide. The IR spectra of these samples with the lowest metal phase content exhibit the pronounced modes from the nanocrystalline MgF$_2$ dielectric phase.