Segregation tendency of Hensler alloys

Abstract

Segregation in a series of Ni2Mn1+x(In, Sn, Ga, Al)(1-x) and Mn2Ni1+x(Ga, Al) as well as Ni2+xMn1-xGa Heusler alloys is studied by first-principles calculations. We show that Mn-rich Ni2Mn1+x(In, Sn, Al)(1-x) compounds are at low temperatures unstable in the whole concentration range against decomposition into a dual-phase system consisting of an L2(1)-cubic Ni2MnX phase with ferromagnetic order and an L1(0)-tetragonal NiMn phase ordered antiferromagnetically. In contrast, Ni2Mn1+xGa1-x and Mn2Ni1+x(Ga, Al)(1-x) are stable in the narrow concentration range near the 2-1-1 stoichiometry. This concentration range depends on the presence of a martensitic transformation and becomes wider with increasing energy difference between austenite and martensite phases in a parent system. We find that ferromagnetic Ni-rich Ni2+xMn1-xGa is stable in the concentration range 0 < x less than or similar to 0.6.