Figure 1: Experimentally obtained “metastable” phase diagram of Ni–Fe alloys (which is adapted in accordance with [2]). The symbol “?” denotes the unidentified authentically structural and/or magnetic states of alloys. 𝛾 -Fe, 𝛼 -Fe, and 𝛿 -Fe are the f.c.c., low-, and high-temperature b.c.c. crystal lattice modifications of an iron. L is the Ni–Fe liquid solution. The equilibrium crystal structures of the three stoichiometric ordered phases at 𝑇 = 0  K (from right to the left), L12-Ni3Fe (Permalloy), L10-NiFe (Elinvar), and L12-NiFe3 (Invar), are also shown (° = Ni, ● = Fe).