Nanocomposites and nanomaterials
Structure and magnetic properties of Co-Cr-Fe-Mn-Ni high-entropy alloy oxide films 
Kushnerov O.I., Ryabtsev S.I., Bashev V.F.  
Department of Experimental and Metal Physics, Oles Honchar Dnipro National University. Gagarin ave., 72, Dnipro, 49010, Ukraine. 
E-mail: kushnrv@gmail.com

The first works related to designing and complex study of a new class of materials, the so-called high-entropy multicomponent alloys (HEAs) were published in 2004. As a rule, these compositions comprise 5–13 principal elements, the concentrations of which are equiatomic or close to equiatomic (5–35%). Choosing a number of components and their concentration allows one to achieve an increased entropy of mixing, which remains not only in the melt but after solidification. Because of the high entropy, usually simple substitutional solid solutions with BCC or FCC crystal lattices are formed during the solidification of such alloys. The HEAs are characterized by a number of useful characteristics, such as hardness, wear resistance, resistance to oxidation, corrosion, and ionizing radiation, biocompatibility, and high thermal stability. At the same time, a relatively small number of papers report the producing of HEA thin films and investigations of their properties as compared with those of bulk alloys.
In this study, Co19Cr18Fe22Mn21Ni20 HEA thin films have been synthesized by ion plasma sputtering of mosaic targets consists of pure metals. The deposition process was carried out at room temperature with Ar atmosphere. Sputtering was carried out on the sitall substrates, as well as on a fresh cleavage of NaCl single crystal. The as-deposited HEA film thickness was estimated to be ~ 110 nm. Films deposited on single-crystal substrates after a dissolution of the salt were used for structural studies by X-ray diffraction analysis. Single diffuse halo is observed on the XRD patterns of the as-deposited films, that confirms their amorphous structure. Some of the thin films were annealed at 600ºC in a vacuum furnace. These films were identified to be oxidized by the small amount of oxygen in the chamber. After the heat treatment in vacuum, the Co19Cr18Fe22Mn21Ni20 metallic film transforms from an amorphous form into a crystallized FCC solid solution structure with the lattice parameter a=0.3613 nm. 
The magnetic properties of the films were measured by a vibrating sample magnetometer at room temperature with the magnetic field applied parallel to the film plane. The as-deposited HEA film exhibits the soft magnetic properties and the coercivity of 5 Oe. After annealing the value of coercivity increase to 110 Oe. So the annealed metal oxide films can be considered as hard magnetic materials.