Propiedades electrónicas y magnéticas de las aleaciones Fe-Al

Abstract

This work presents ab-initio self-consistent calculations performed with the TB-LMTO code to study the different phases of the Fe-Al phase diagram, corresponding to the ordered structures B2, DO3 and B32 and for Fe 50 Al 50 and Fe 3 Al compositions. Both, unpolarized and spin-polarized calculations have been performed to deduce the energetic difference between the paramagnetic and ferromagnetic state of the corresponding structure. Calculations for the disordered structures have also been performed for the previously mentioned compositions. These results show that by disordering the alloy magnetism is enhanced and that the equilibrium lattice parameter increases. Keywords: Fe-Al alloys, TB-LMTO code, magnetic transformations, order-disorder. Propiedades electrónicas y magnéticas de las aleaciones Fe-AlEn este trabajo se presentan cálculos autoconsistentes ab-initio realizados con el método TB-LMTO (Tight Binding Linear Muffin Tin Orbital) con el fin de estudiar las diferentes estructuras que se presentan en el diagrama de fases de las aleaciones Fe-Al. Se han estudiado las estructuras ordenadas B2, DO3 y B32 para las siguientes concentraciones: Fe50Al50 y Fe3Al. Asimismo, se han realizado cálculos teniendo y sin tener en cuenta la polarización de spin con el fin de poder deducir la diferencia energética entre los estados ferromágneticos y paramágneticos de la misma estructura. Por otra parte se han realizado estos mismos cálculos para estructuras desordenadas y las mismas concentraciones. Los resultados muestran que mediante el desorden aumenta el magnetismo de estas aleaciones y crece el parámetro de red. Palabras clave: Aleaciones Fe-Al, código TB-LMTO, transformaciones magnéticas, orden-desorden.room temperature), B32 long range order was observed by Becker and Schweike in neutron scattering experiments (4). Calculations of model alloys show that the B32 phase has a tendency to exist at even larger deviations from stoichiometry than the B2 phase.It has been shown that these alloys are of the ferromagnetic disordered type (BCC, A2) for Al concentrations up to 23 at % Al independent of heat treatment (5). In alloys with Al content ranging from 0 to 30 at % the iron atoms carry their normal magnetic moment of 2.2 µ B when they have at least five or more iron atoms as nearest neighbours (6). The 30 at % Al composition is critical for these systems were the average magnetic moment per Fe atom decreases rapidly from 2.0 to 0.7 µ B ; coupled with this there is a large fall in the lattice parameter associated with a fall in the atomic radii as the disorder to order transition occurs (20 to 30 at % Al).By disordering the alloy paramagnetic-ferromagnetic transitions can be induced and these transitions could be related to the changes in volume and not only to nearest neighbour effects as is commonly assumed. As an example we can mention that x-ray diffraction of ball milled alloy of composition Fe 60 Al 40 shows an increase of the lattice parameter with milling time (7). This lattice parameter increase has been assumed...

Electronic structure of FeAl alloy studied by resonant photoemission spectroscopy and Ab initio calculations

“…Room temperature XRD patterns recorded at 19.3 keV X-ray energy are shown in figure 1(a). All the peaks could be indexed to a cubic structure using Le-Bail fitting, with a lattice constant of a= 2.917 Å, which is in good agreement with the lattice parameter reported in literature [26,27,28,29]. The presence of (100) peak in the pattern clearly indicates the presence of an ordered B2 phase in the sample.…”