Stability of the Fe fcc phase (gamma-Fe) is defined by metal bonds of 4s- and a part 3d(t_2g)-electrons and by covalent interactions of 3d(e_g)- and a part of 3d(t_2g)-electrons. The hybridization of electrons of the high (e_g) 3d-level and 4s-band results in DOS peaks and antipeaks of band electrons (DOS - 4s - e_g). In exactly the same way, the total transfer integral for band and covalent 3d(t_2g)-electrons results in anomalies of DOS - t_2g near the Fermi surface. Bonding covalent energies of parts of e_g and t_2g-electrons provide the stability of gamma-Fe at heating, though the occurrence of a soft mode of chemical (covalent) bond fluctuations (CBF) under pressure P, which destabilizes the fcc lattice, is possible. The antibonding covalent energy of the nearest neighbours is responsible for gamma-Fe antiferromagnetism. It gives the excess of the fcc lattice free energy above those for a bcc lattice, in which the bonding covalent energy of the nearest neighbours is responsible for alpha-Fe ferromagnetism. This excess explains the distinction of magnetic states of gamma-Fe and alpha-Fe and the stability of bcc alpha-Fe at low temperatures T < T₀, where T₀(P, x) is the line of polymorphous alpha - gamma-transitions for the impurity concentration x.

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