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

We pursued a theoretical investigation of the Ni-Mn-Ga Heusler alloy to understand the role of magnetism on the lattice stability and, consequently, the magnetic shape memory (MSM) effect. Two<i>ab initio</i>methods were used for the calculations: the widely used standard density functional theory and the advanced quasiparticle self-consistent<i>GW</i>(QSGW) method. The latter is expected to be more accurate due to the explicit inclusion of electron correlation. The generalized susceptibility calculated by QSGW indicated that the existence of magnetic ordering in the high temperature phase, austenite, is crucial for the formation of the modulated martensites. The ferromagnetic austenite transforms into modulated martensites that can exhibit MSM, but the paramagnetic austenite does not possess this tendency in accordance with experimental observations. In the non-modulated tetragonal martensite (NM), we investigated the role of magnetic ordering on the stability of the lattice and twinning interface. We found that the elastic constants remain unchanged during magnetic moment rotation, confirming the stability of NM in agreement with the notion that it is a ground state. Furthermore, the calculation revealed that the magnetization rotation has a negligible influence on the stability of the twinning interface in NM.