Metastable states and physical properties of Co-Cr-Fe-Mn-Ni high-entropy alloy thin films

Abstract

In this study, Co19Cr18Fe22Mn21Ni20 HEA thin films have been obtained by the modernized method of three-electrode ion-plasma sputtering of mosaic targets consisting of pure metals. The structure, electrical resistance and magnetic properties of films were investigated. Single diffuse halo is observed on the XRD patterns of the as-deposited films, which confirms their amorphous structure. Some of the thin films, which were annealed at 900 K in a vacuum were identified to be oxidized by the small amount of oxygen in the work chamber. After the heat treatment, the Co19Cr18Fe22Mn21Ni20 films are transformed from an amorphous state into a crystallized FCC solid solution with the lattice parameter a = 0.3613 nm. Also, the cubic B2 phase of FeCo with a lattice parameter of 0.2857 nm is formed in the annealed films. As a result of oxidation processes, a dispersed phase of manganese oxide is also arising after annealing. Calculation of the activation energy of the beginning of phase transition was carried out by the generalized Kissinger method. The temperature dependencies of electrical resistivity of films were measured by the four-point technique upon continuously heating in the high vacuum. Both as-deposited and annealed films clearly reveal a typical ferromagnetic behavior. The as-deposited HEA film exhibits the soft magnetic properties while the annealed films can be attributed to hard magnetic materials.