Unraveling Magnetic Properties and Martensitic Transformation in Mn-rich Ni–Mn–Sn Alloys: First-Principles Calculations and Experiments

We have investigated the phase stability, magnetic properties, and martensitic transformation thermodynamics/kinetics of the Ni24-xMn18+x+ySn6-y (x, y = 0, 1, 2) system by combining the first-principles calculations and experiments. The calculation results show that the optimized lattice parameters are consistent with the experimental data. Respectively, we obtain the relation equation for the austenite formation energy (Eform-A) and Mn content (XMn): E_form - A = 507.358X_Mn -274.126 , as well as for the six-layer modulated (6M) martensite formation energy (Eform-6M) and Ni content (XNi): E_form - 6M = - 728.484X_Ni + 264.374 . The ternary phase diagram of the total magnetic moment was established. The excess Mn will reduce the total magnetic moment of 6M (Mag6M) and non-modulated (NM) (MagNM) martensites, with the following equations relating the total magnetic moment and Mn content: Mag_6M = - 15.905X_Mn + 7.902 and Mag_NM = - 14.781X_Mn + 7.411 , while the effect on austenite is complex. The variation of total magnetic moment is mainly dominated by the Mn atomic magnetic moment. The 3d electrons of MnSn (Mn at Sn sublattice) play an important role in magnetic properties from the perspective of the electronic density of states. Based on the thermodynamics of martensitic transformation, the alloys will likely undergo austenite ↔ 6M ↔ NM transformation sequence. Combining the thermodynamic and kinetic results, the martensitic transformation temperature decreases with x increasing and increases with y increasing. These results are expected to provide reference for predicting the phase stability and magnetic properties of Ni–Mn–Sn alloys.