Driving force for martensitic transformation inNi2Mn1+xSn1−x

Abstract

The martensitic transformation in Ni 2 Mn 1+x Sn 1−x alloys has been investigated within ab-initio density functional theory. The experimental trend of a martensitic transition happening beyond x = 0.36 is captured within these calculations. The microscopic considerations leading to this are traced to increased Ni-Mn hybridization which results from the Ni atom experiencing a resultant force along a lattice parameter and moving towards the Mn atoms above a critical concentration.The presence of the lone pair electrons on Sn forces the movement of Ni atoms away from Sn.While band Jahn Teller effects have been associated with this transition, we show quantitatively that atleast in this class of compounds they have a minor role.

Impact of Co and Fe Doping on the Martensitic Transformation and the Magnetic Properties in Ni‐Mn‐Based Heusler Alloys

“…For all the systems in the AFM E state, the global minimum lies for which correspond to the non‐modulated martensite phase. This implies that the AFM E state stabilizes the martensitic phase . The computed lattice parameters for the tetragonal martensite phase are presented in Table .…”

Properties of Magnetic Shape Memory Alloys in Martensitic Phase

“…The martensitic crystal structure is tetragonal with Fmmm space group for Ni 2+x Mn 1-x Ga ( Figure 4; a = b = 5.469 Å and c = 6.517 Å Table 2. Structural and magnetic transition temperatures of Ni2Mn1+xIn1-x obtained from DSC 346 317 329 359 390 NCMI2 335 292 312 349 397 has a similar tetragonal martensitic crystal structure (space group Fmmm) as shown in Figure 5 for Ni The ab initio calcuation 40 for Ni 2 Mn 1+x Sn 1-x shows that with increase in Mn2 concentration, the Ni atoms move towards both Mn1 and Mn2. The resultant movement is along a lattice parameter.…”

“…36). The ab initio electronic structure calculations for Ni 2 Mn 1+x Sn 1-x were carried out using the PAW method as implemented in the VASP code within GGA for the exchange correlation functional 40 . A supercell consisting of 5  5  1 primitive cells of the L2 1 crystal structure was considered to calculate the behaviour of excess Mn substitution at Sn sites 41 .…”

“…The effect of Ni 3d-Mn 3d state hybridization is manifested through Ni satellite 55 . The martensitic transformation in Ni 2 Mn 1+x Sn 1-x alloys has been studied within ab initio DFT 40 . The martensitic transformation is obtained for x = 0.375, which is in good agreement with the experimental value of x = 0.36.…”

Magnetic Order and Lattice Instabilities in Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$ Heusler based Magnetic Shape-Memory Alloys

“…However, in contrast to these results, a very recent work calculated the relative on-site energies of Ni d states using tight binding model for the Ni 2 Mn 1.5 Sn 0.5 alloy and found that these energies are small. Based on these results, the authors ruled out the possibility of Jahn-Teller distortions [17] and suggested that Ni-Mn hybridization and impact of Sn lone pair is responsible for the MPT. Furthermore, extended X-ray absorption fine-structure (EXAFS) measurements suggest that local structural distortions upon excess Mn doping play a crucial role for the austenite to martensitic phase transition [18].…”