Structural, electronic, and magnetic properties of 3dtransition-metal aluminides with equiatomic composition

First-principles calculations have been performed to study the chemical bonding trends and the phase stability of 3d transition-metal (TM) aluminides with equiatomic composition. The physical mechanisms for ordering in both the L$1_0$ and B2-type aluminides are presented. It is shown that the dominant factor for early TM aluminides is the directional bonding between the d orbitals of TM atoms, whereas for late TM aluminides, charge transfer and hybridization between Al s and p states, and TM d states play more important roles in the bonding mechanism and the properties of lattice defects. Our calculations also show the existence of a ferromagnetic phase for MnAl in the L$1_0$ structure, which is stabilized by the formation of a magnetic moment on the Mn sites (with a value of 2.0 ${\mathrm{\mu }}_{\mathit{B}}$). The chemical trends in the structural stability and heats of formation of 3d TM aluminides are found to correlate well with the densities of states at the Fermi level.