First-principles study of electronic and magnetic properties and tetragonal distortion of the Heusler alloy Mn<sub>2</sub>NiAl

Abstract

The crystal structure, tetragonal distortion, magnetism, electronic structure and pressure response of Mn2NiAl are calculated by first-principles method based on the den- sity functional theory. The calculations show, the equilibrium structure of Mn2NiAl in the cubic austenitic phase is the MnMnNiAl structure with Mn atoms occupy A and B sites and two Mn atoms occupy inequivalent positions. In the process of transform from a cubic to a tetragonal structure, Mn2NiAl alloys exhibit a stable martensitic phase near c/a=1.24. In both the austenite and martensite phases, Mn atoms are the main contributors to the magnetism in Mn2NiAl, Mn2NiAl alloys show ferrimagnetism due to antiparallel but un- balanced magnetic moments of Mn(A) atom and Mn(B) atom. The direct d-d exchange interactions between Mn(A) atom and Mn(B) atom are weak because of small overlap of d-projected DOS of Mn(A) atom and Mn(B) atom nearby the Fermi level, but the intra- atomic interactions in Mn atoms are strong, this is the reason why the Mn2NiAl alloys show ferrimagnetism. The findings strongly suggests that Mn2NiAl alloys would behave like a magnetic shape memory alloy.