Role of magnetic ordering on transformation properties of Heusler Ni ₂ MnGa magnetic shape memory alloy

We pursued a theoretical investigation of Ni-Mn-Ga Heusler alloy to understand the role of magnetism on the lattice stability and consequently on the magnetic shape memory (MSM) effect. Two ab initio methods were used for the calculations which are the widely used standard density functional theory (DFT) and the advanced quasiparticle self-consistent GW (QSGW) method. The latter is expected to be more accurate due to the inclusion of explicit electron correlation. Calculated generalized susceptibility, one of the electronic structure properties, indicated that the existence of magnetic ordering in high temperature phase, austenite, is crucial for the formation of the modulated martensites. The ferromagnetic austenite transforms to the modulated martensites, but the paramagnetic austenite does not in agreement with experimental observations. Additionally, we investigated the role of magnetic ordering on the stability of lattice and twinning interface of the nonmodulated martensite (NM). We found that the elastic constants stay constant under the change of magnetic moments orientation, confirming the stability of NM in agreement with notion that it is a ground state. Further, the calculation revealed that the rotation of magnetization has negligible influence on the stability of twinning interface in NM, suggesting that another effect may be decisive for the unique behavior of the twinning interface in 10M Ni-Mn-Ga martensite.