Electronic structure and possible martensitic transformation in Mn2NiGe and Ni2MnGe

The electronic structure and magnetism of Heusler alloys Mn2NiGe and Ni2MnGe have been studied by first-principles calculations. The possible non-modulated tetragonal martensitic transformation in them has been predicted. For both Mn2NiGe and Ni2MnGe, the tetragonal martensitic phase is lower in energy compared with the cubic austenitic phase. In Ni2MnGe, the martensitic transformation follows the conservation of volume. But in Mn2NiGe, a small contraction of the martensitic cell volume is predicted. The energy difference ΔE between the martensitic and austenitic phase is −8 meV/cell in Ni2MnGe and −80 meV/cell in Mn2NiGe, so it is more likely to observe martensitic transformation in Mn2NiGe or Heusler alloys with similar compositions. Ni2MnGe is found to be a ferromagnet, while Mn2NiGe is a ferrimagnet in which the Mn spin moments are in antiparallel coupling.