Ab-initio revelation on the origins of Ti substitution for Ga, Mn and Ni on ferromagnetism, phase stability and elastic properties in Ni2MnGa

Abstract

In the present work, the effects and the underlying mechanisms of Ti substitution for Ga, Mn and Ni on ferromagnetism, phase stability, elastic properties and electronic structures in Ni2MnGa alloy were studied by first-principles calculations. Upon substitution for Ga or Mn, the Ti prefers to directly take the Ga or Mn sites. However, when Ti replaces Ni, the Ti likes to take the site of Mn atom that occupies the Ni site. When Ti replaces Ga, the magnetism is insensitive to the Ti content. On the contrary, when Ti replaces Mn and Ni, both the magnetization and Curie temperature of the alloy are greatly reduced, which are resulted from the reduced Mn content and the indirect occupation manner of Ti, respectively. For the lattice stability, Ti replacement for Ga or Mn (Ni) reduces or enhances the stability of austenite, respectively. Additionally, Ti substitution for Ga could be an effective strategy to tailor c/a ratio of the martensite. As for the elastic properties, we find that Ti substitution for Ga can reduce the intrinsic brittleness of the alloy owing to the decreased p-d hybridization between Ni–Ga. By contrast, the Ti replacement for Ni is harmful to ductility, but can greatly enhance the intrinsic strength of the alloy owing to the coexistence of the p-d bonds between Ni–Ga and Mn–Ga, and the d-d bonds between Ni–Ti and Mn–Ti.