Invar behavior of disorderedfcc−FexPt1−xalloys

Abstract

Using the tight-binding linearized muffin-tin orbital method combined with the coherent-potential approximation (TB-LMTO-CPA) we have calculated the electronic and magnetic structure of disordered fcc ${\mathrm{Fe}}_{x}{\mathrm{Pt}}_{1\ensuremath{-}x}$ alloys in a broad concentration range. The total energy was determined as a function of the lattice constant and of the magnetic moment (fixed-spin moment method). For iron concentrations between $x=0.10$ and $x=0.85$ the equilibrium lattice constant, the bulk modulus, and the magnetic moment were determined in good agreement with available experimental data. No deviations of the magnetization from the Slater-Pauling curve in the Invar region were found. In that region two minima of the total energy exist, one with a high moment and a large lattice constant and the other with a zero moment and a small lattice constant, which explains qualitatively the Invar effect. Both minima become degenerate at the critical concentration, ${x}_{c}=0.76.$ A nonmagnetic ground state was found for $xg{x}_{c}.$ The energy barrier separating these two minima is two times higher in FePt Invar alloys than in the FeNi system. The relativistic effects were included within the scalar relativistic approximation.