Theoretical design of Ti2-based magnetic shape memory alloys from first-principles

Magnetic shape memory alloys (MSMAs) typically comprise transition metal and main group atoms. We developed a class of Ti ₂-based Heusler MSMAs formed by transition metal and metalloid elements using the first-principles calculation method based on density functional theory. For all the studied Ti ₂ YZ ( Y = Cr, Mn, Fe, and Co; Z = B, Si, Ge, As, Sb, and Te) Heusler alloys, the calculated formation energies in the austenitic phase show that, except for Ti ₂CrTe, all alloys have thermodynamic stability. Based on a comprehensive analysis of the total energy difference between austenite and martensite, the density of states (DOS), and the bulk mechanical properties, we predict that of all the Ti ₂-based alloys studied here, 17 alloys are likely to undergo a martensitic phase transition. The DOS of the cubic structures reveals that the substantial peak structures around the Fermi level, mainly formed by strong hybridization between the Ti atom and its neighbor Y and Z atoms, lead to cubic instability. Compared with the typical MSMA of Ni ₂MnGa, most Ti ₂ YZ alloys possess a larger martensitic driving force, a higher martensitic transition temperature, and better ductility. Therefore, our study could inspire the development and application of new Ti ₂-based MSMAs.