Electronic and Vibrational Properties of Fe2NiAl and Co2NiAl Full Heusler Alloys: A First-Principles Comparison

In this work, we report on a systematic first-principles study of the structural, electronic, vibrational and thermodynamic properties of the cubic Fe₂NiAl and tetragonally distorted Co₂NiAl full Heusler compounds. We discuss systematically the competition between the inverse Heusler structure and a T^p-type layered atomic ordering formed by the alternating planes of (Fe,Co) and Ni atoms in terms of the electronic and vibrational density of states.

Such an arrangement is predicted to be the ground state of Fe₂NiAl. For Co₂NiAl, layered ordering has slightly higher energy in comparison with the inverse one, however, we show that it might be stabilized at rather low temperatures.

Due to the broken symmetry, layered T^p-Fe₂NiAl possesses a large MAE of the same order as tetrataenite FeNi - even in a phase with cubic lattice parameters, which makes a T^p-type layered order an interesting feature for rare-earth free permanent magnets in Heusler-type compounds.