INVAR BEHAVIOR OF DISORDERED FCC-FEXPT1-X ALLOYS

Using the tight-binding linearized muffin-tin orbital method combined with the coherent-potential approximation (TB-LMTO-CPA) we have calcul ated the electronic and magnetic structure of disordered fcc FexPt1-x alloys in a broad concentration range. The total energy was determined as a function of the lattice constant and of the magnetic moment (fix ed-spin moment method). For iron concentrations between x = 0.10 and x = 0.85 the equilibrium lattice constant, the hulk modulus, and the ma gnetic moment were determined in good agreement with available experim ental data. No deviations of the magnetization from the Slater-Pauling curve in the Invar region were found. In that region two minima of th e total energy exist, one with a high moment and a large lattice const ant and the other with a zero moment and a small lattice constant, whi ch explains qualitatively the Invar effect. Both minima become degener ate at the critical concentration, x(c) = 0.76. A nonmagnetic ground s tate was found for x>x(c). The energy barrier separating these two min ima is two times higher in FePt Invar alloys than in the FeNi system. The relativistic effects were included within the scalar relativistic approximation.