Electronic structure of the ordered phases of Pt-Fe alloys

The electronic structure of several ordered phases of the Pt-Fe system is studied using the self-consistent linear muffin-tin-orbital method. The phases studied include nonmagnetic and ferromagnetic ${\mathrm{PtFe}}_3$, ferromagnetic ${\mathrm{Pt}}_2$ ${\mathrm{Fe}}_2$, antiferromagnetic and ferromagnetic ${\mathrm{Pt}}_3$Fe, and ferromagnetic ${\mathrm{Pt}}_5$ ${\mathrm{Fe}}_3$. The electronic structure, the densities of states, and the ground-state properties, such as equilibrium lattice constants, bulk moduli, local and average magnetic moments, and the state equations are calculated. The calculated parameters compare favorably with existing experimental data. The cohesive properties, chemical bonding, and the moment-stabilizing mechanism are discussed. A variation of all these aspects with alloy composition illustrates a continuous transition from itinerant to local-moment magnetism. An interplay of the covalent bonding, scalar relativistic effects, electronegativity, and the charge transfer is shown to be responsible for this transition. Homogeneity of the magnetic state of ${\mathrm{PtFe}}_3$ Invar is explained. On the basis of the calculated elastic properties and recently reported critical pressures at which the magnetic moment of ${\mathrm{PtFe}}_3$ collapses, the total energy difference between the ferromagnetic and nonmagnetic phase is estimated.