The features of CoFeZr alloy nanocrystals formation in film composites of (CoFeZr)x(MgF2)100-x

Highlights: • Nanocomposites of variable composition (CoFeZr)_x(MgF₂)_100‐x by XRD, XPS, and IR-spectroscopy methods were investigated. • The formation of CoFeZr nanocrystals in an amorphous MgF₂ dielectric matrix occurs with x increasing in the process of self-organization. • XPS studies confirm the presence of a predominant type of metal bonds in clusters and nanocrystals of CoFeZr. -- Abstract: The influence of relative content of the metal component on the phase composition and substructure of (CoFeZr)_x(MgF₂)_100−x film nanocomposites between x = 7÷51 (at%) has been established by X-ray diffraction (XRD), X-ray electron spectroscopy (XPS) and infrared spectroscopy (IR). Ion-beam sputtering of a composite target from Co₄₅Fe₄₅Zr₁₀ amorphous alloy plate with MgF₂ dielectric inserts allow prepared micron-thick nanocomposite layers in the argon atmosphere. The results show that at a relatively low content < 25, the CoFeZr metal alloy is in the X-ray amorphous state in the nanocrystalline MgF₂ matrix. The IR spectra of these samples show a clear formation of modes in the range of 400–600 cm⁻¹ from nanocrystals of the MgF₂ dielectric matrix. With an increase of the metal component content for >25, the MgF₂ matrix becomes X-ray amorphous, and CoFeZr alloy nanocrystals of the hexagonal syngony based on the α-Co structure with dimensions of about 10 nm are first formed; they are predominantly oriented in the plane of the hexagonal lattice (001). With a further increase of the metal alloy content up to ~40 in the region nearer to the percolation threshold, the crystal structure of nanocrystals of the CoFeZr alloy becomes a cubic phase based on α-Fe with a preferred orientation of (110). XPS studies confirm the presence of a predominant type of metal bonds in clusters and nanocrystals of CoFeZr, despite the oxidation of the thinnest surface layers, as well as ionic bonds in the MgF₂ dielectric matrix, preserved because of self-organization even in non-equilibrium conditions of ion-plasma sputtering. Two features on the curve of the dependence of the resistivity of nanocomposites on the alloy concentration are due to: the first one (x~25) - the formation of nanocrystals of hexagonal symmetry from clusters of the amorphous CoFeZr alloy, and the second one (x~40) nearer the percolation threshold - coincides with the phase transition of nanocrystals from hexagonal to cubic structure.