title: First-principles study of the lattice instabilities in Mn2NiX (X = Al, Ga, In, Sn) magnetic shape memory alloys.
abstract: Using first-principles based density functional theory, we have investigated the structural instabilities in the austenite phases of Mn(2)NiX (X = Al, Ga, In, Sn) magnetic shape memory alloys. A complete softening is observed in the acoustic TA(2) branches for all the materials along [ξξ0] directions leading to instability in the austenite structure which effectively stabilizes into martensitic structure. The reasons behind this softening are traced back to the repulsion from the optical T(2g) branches and to the nesting features in the Fermi surfaces. The vibrational density of states, the force constants and the elastic moduli are also computed and analyzed, which reconfirm the underlying mechanism behind the instabilities. The results indicate that the phonon anomalies are related to the occurrence of possible pre-martensitic phases which can be quite complex.
authors.affiliation: Department of Physics, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.
authors.forename: Souvik
authors.initials: S
authors.lastname: Paul
authors.forename: Biplab
authors.initials: B
authors.lastname: Sanyal
authors.forename: Subhradip
authors.initials: S
authors.lastname: Ghosh