Impact of local arrangement of Fe and Ni on the phase stability and magnetocrystalline anisotropy in Fe-Ni-Al Heusler alloys

Abstract

On the basis of density functional calculations, we report on a comprehensive study of the influences of atomic arrangement and Ni substitution for Al on the ground-state structural and magnetic properties for ${\mathrm{Fe}}_{2}{\mathrm{Ni}}_{1+x}{\mathrm{Al}}_{1\ensuremath{-}x}$ Heusler alloys. We discuss systematically the competition between five Heusler-type structures formed by shuffles of Fe and Ni atoms and their thermodynamic stability. All Ni-rich ${\mathrm{Fe}}_{2}{\mathrm{Ni}}_{1+x}{\mathrm{Al}}_{1\ensuremath{-}x}$ tend to decompose into a dual-phase mixture consisting of ${\mathrm{Fe}}_{2}\mathrm{Ni}\mathrm{Al}$ and FeNi. The successive replacement of Ni by Al leads to a change of ground-state structure and eventually an increase in magnetocrystalline anisotropy energy (MAE). We predict for stoichiometric ${\mathrm{Fe}}_{2}\mathrm{Ni}\mathrm{Al}$ a ground-state structure with nearly cubic lattice parameters but alternating layers of Fe and Ni possessing a uniaxial MAE that is even larger than tetragonal $L{1}_{0}$-FeNi. This opens an alternative route for improving the phase stability and magnetic properties in FeNi-based permanent magnets.