Effects of order on the electronic structure of ferromagnetic transition metal alloys: application to FeCo and Ni₃Fe

Abstract

The electronic structures of ordered and disordered transition metal alloys are described in a tight-binding scheme. Charge transfer and magnetism are treated within a self-consistent Hartree-Fock model. We show that the rigid band splitting fails to take account of the ferromagnetism of these compounds. The densities of states of FeCo and Ni,Fe are found to be more sensitive to order than the ferromagnetic properties. Energetic calculations are performed giving an estimation of the ordering energy, and comparisons are made with experimental results.

Effects of Order on the Electronic Structure of Ni3Fe

“…The electronic specific heat coefficient y deduced by u!j from the density of states a t the B'ermi level for the disordered alloy is 2.73 m J mol-l K-2. Desjonqueres and Lavagna obtained 3 niJ mol-l K-2 and the experimental result is 3.88 niJ mol-l K-2 [6]. The Fermi level lies inside an enhanced peak and the density of states for this energy value is very sensitive to the choice of parameters.…”

“…The only comparison of the electronic structure of ferromagnetic f.c.c. ordered and perfectly disordered alloys has been given by Desjonqueres and Lavagna [6]. They used a multiorbital tight binding model with diagonal and off-diagonal disorder, the latter taken into account in Shiba's formalism.…”

Effects of short-range order and long-range order on the low-temperature specific heat of Ni3Fe alloys

“…When the spin-wave contribution to c p is negligible, equation (2) may be rewritten as a linear function of T2 10 75 20 25…”

“…A more recent study, by Desjonqueres and Lavagna [25], has been devoted to the electronic structure of FeCo and Ni,Fe alloys in connection with the order-disorder Ni (of%)transition. For the FeCo alloy, the values of the electronic specific heat deduced from the calculated density of states a t are in good agreement with the experimental results of Kuentzler [6].…”

“…Moreover they claim that for a rather small variation in composition the model of the rigid 3d band can be used for Ni,Fe. Then it may be thought that the substitution of Ni in Ni,Fe with Fe displaces E~ downwards in energy and according to the N ( E ) curve for ordered Ni,Fe [25] the Fermi level moves towards the minimum of the curve. I n moving E~, the decrease of energy on ordering AE and therefore the critical temperature T, of the order-disorder phase transition are expected to vary and AE will be the largest a t the composition for which T, is the highest (72.5 atyo Ni) .…”