First-principles study of the lattice instabilities in Mn${}_2$Ni{\it X} ({\it X}= Al, Ga, In, Sn) magnetic shape memory alloys

Abstract

Using first-principles based Density Functional Theory (DFT), we have investigated the structural instabilities in the austenite phases of Mn${}_2$Ni{\it X} ({\it X}= Al, Ga, In, Sn) magnetic shape memory alloys (MSMA). A complete softening is observed in the acoustic TA${}_2$ branches for all the materials along [$\xi \xi$0] directions leading to the instability in the austenite structure which effectively stabilizes into martensitic structure. The reasons behind this softening are traced back to the repulsion from the optical T${}_{2g}$ branches and to the nesting features in the Fermi surfaces. The vibrational density of states, the force constants and the elastic moduli are also computed and analyzed, which reconfirm the underlying mechanism behind the instabilities. The results indicate that the phonon anomalies are related to the occurrence of possible pre-martensitic phases which can be quite complex.

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• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Martensitic transition, ferrimagnetism and Fermi surface nesting in Mn_2NiGa
• Lattice dynamics of the high temperature shape memory alloy Nb-Ru
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Cited by in corpus (1)

• Large magnetocrystalline anisotropy in tetragonally distorted Heuslers: a systematic study