Segregation in a series of ${\mathrm{Ni}}_2{\mathrm{Mn}}_{1+x}{(\mathrm{In},\mathrm{Sn},\mathrm{Ga},\mathrm{Al})}_{1-x}$ and ${\mathrm{Mn}}_2{\mathrm{Ni}}_{1+x}$(Ga, Al) as well as ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1-x}\mathrm{Ga}$ Heusler alloys is studied by first-principles calculations. We show that Mn-rich ${\mathrm{Ni}}_2{\mathrm{Mn}}_{1+x}{(\mathrm{In},\mathrm{Sn},\mathrm{Al})}_{1-x}$ compounds are at low temperatures unstable in the whole concentration range against decomposition into a dual-phase system consisting of an $L{2}_1$-cubic ${\mathrm{Ni}}_2\mathrm{Mn}X$ phase with ferromagnetic order and an $L{1}_0$-tetragonal NiMn phase ordered antiferromagnetically. In contrast, ${\mathrm{Ni}}_2{\mathrm{Mn}}_{1+x}{\mathrm{Ga}}_{1-x}$ and ${\mathrm{Mn}}_2{\mathrm{Ni}}_{1+x}{(\mathrm{Ga},\mathrm{Al})}_{1-x}$ 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 ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1-x}\mathrm{Ga}$ is stable in the concentration range $0<x\lesssim 0.6$.

• Received 15 February 2019
• Revised 17 July 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.3.084413