A critical discussion of calculated modulated structures, Fermi surface nesting and phonon softening in magnetic shape memory alloys Ni$_2$Mn(Ga, Ge, Al) and Co$_2$Mn(Ga, Ge)

TL;DR

This paper uses first principles calculations to analyze electronic and phonon properties of certain Heusler alloys, revealing the importance of Fermi-surface nesting and phonon hybridization in martensitic transformations.

Contribution

It provides new insights into the mechanisms driving structural instabilities and martensitic transformations in Ni$_2$Mn(Ga, Ge, Al) and Co$_2$Mn(Ga, Ge) alloys through detailed electronic and phonon analysis.

Findings

Fermi-surface nesting influences structural stability.

Hybrid phonon modes are crucial for modulated structures.

Electronic peculiarities relate to martensitic transformations.

Abstract

A series of first principles calculations have been carried out in order to discuss electronic structure, phonon dynamics, structural instabilities and the nature of martensitic transformations of the Heusler alloys Ni$_2$Mn(Ga, Ge, Al) and Co$_2$Mn(Ga, Ge). The calculations show that besides electronic pecularities like Fermi--surface nesting, hybridizing optical and acoustic phonon modes are important for the stabilization of the modulated martensitic structures.