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. -Fe, -Fe, and -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  K (from right to the left), L1₂-Ni₃Fe (Permalloy), L1₀-NiFe (Elinvar), and L1₂-NiFe₃ (Invar), are also shown (° = Ni, ● = Fe).