Electronic structure and transport properties of Fe–Al alloys

Electronic structure of iron-aluminides (Fe1−xAlx) has been calculated for a range of aluminum concentration (0⩽x⩽0.5) by using first principles density functional theory to explain the variation of electrical resistivity with increasing Al content. The Fe–Al intermetallics are modeled by a cluster of 15 atoms confined to their bulk geometry. The location of Al atoms as a function of concentration, x was determined by minimizing the total energy of the clusters. The electronic structure was determined by calculating the total as well as partial density of states around each of the Fe and Al atoms. With increasing Al concentration, the transfer of Al 3p electrons into the minority 3d orbital of Fe not only has a profound effect on the magnetic properties of these intermetallics, but affects their transport properties as well. For example, the observed anomaly in the electrical resistivity of Fe1−xAlx that peaks at x=0.33 is found to be a direct consequence of the filling of the Fe 3d orbital with Al valence electrons. The density of states is characterized by three distinct features: a narrow 3d band just below the Fermi energy originating from the Fe atoms, an Al s-band lying deeper in energy, and an Al p-band above the Fermi energy. The energy gap between Al 3p and Fe 3d density of states decreases with increasing Al concentration and for x=0.40, the density of states at the Fermi energy is a strongly hybridized p–d state giving Fe1−xAlx metallic-like properties. These features are consistent with the recent photoemission studies carried out at the synchrotron facility at Lawrence Livermore National Laboratory. An anomaly in the temperature dependence of electrical resistivity is also explained in terms of the unique electronic and magnetic structure of these intermetallics.