Electronic Structure and Spin Fluctuations in the fcc Fe?Pd System

Abstract

The electronic structure of the fcc Fe~Pd alloy system is investigated by band structure calculations employing the augmented spherical wave (ASW) method. The three compositions Fe3Pd, FePd and FePd3 are studied assuming the ordered CU3Au and the CuAu structure respectively. The total energy is computed as a function of volume and magnetic moment E(V, lvJ) by performing fixed spin moment (FSM) calculations for all three systems. The energy surface of Fe3Pd shows two minima, a ground state with an average magnetic moment of 2· Olj1.B/atom and a metastable minimum with a very small moment. The intermetallic compound FePd shows the usual behaviour of a strong itinerant ferromagnet with an average magnetic moment of 1· 56j1.B, where iron carries about 2· 8j1.B as for the high-spin state of pure fcc Fe. In FePd3 the iron states form rather localised bands and the magnetic moment rises to 3·2j1.B. Inclusion of spin fluctuations allows treatment of the finite-temperature behaviour of such systems. The magnetic contribution to the thermal expansion coefficient at room temperature for Fe3Pd is Qm::::; -18xlO~6 K~l, which largely compensates the positive phonon (Griineisen) part of Q.