Uncovering the origin of physical properties associated with magneto-structural transition of Ni-Mn-In-X alloys by ab initio methods

Ni-Mn-In metamagnetic shape memory alloys exhibit magneto-structural coupling features during martensitic transformation. In the present work, the composition-dependent crystal structure, phase stability, elastic and magnetic properties of the off-stoichiometric Ni2Mn1.5In0.5 alloy doped with the fourth element X (X = Co, Fe, and Cu) are investigated by using the ab initio calculations. Results show that Co prefers to occupy the Ni sublattice, Fe or Cu takes the Mn site. Doping X constituent reduces the stability of the austenite (A) and non-modulated (NM) martensite. For doped Co, martensitic transformation can occur at 0 <= x <= 0.75, and there exists a magneto-structural coupling characteristic with the Co range in 0 <= x <= 0.25. For the case of Fe or Cu doping, the martensitic transformation is accompanied by the change of magnetism. The results of elastic properties indicate that the plasticity and toughness increase significantly with Fe or Cu doping and decrease with Co doping. Furthermore, the origin of the physical properties associated with the magneto-structural coupling transition is explained in terms of the electronic density of states.