Mechanism for modulated structures in Ni-Mn-Ga: An EXAFS Study

TL;DR

This study uses EXAFS measurements to analyze local atomic structures in Ni-Mn-Ga alloys, revealing structural distortions and orbital hybridizations responsible for martensitic modulations.

Contribution

It provides a detailed scheme of atomic distortions and orbital hybridizations associated with the martensitic phase transition in Ni-Mn-Ga alloys.

Findings

Identification of structural distortions in the L1$_0$ sub-cell

Evidence of hybridization changes in Ga-$p$ and Ni-$d$ orbitals

Insights into local symmetry breaking during martensitic transition

Abstract

The local atomic structure of Ni-Mn-Ga alloys was explored using Mn and Ga K-edge extended X-ray fine structure (EXAFS) measurement. The changes occuring in the L1$_0$ sub-cell of the martensitic unit cell and the bond lengths obtained from the analysis enables us to propose a scheme for the structural distortions responsible for the modulations and shuffling of the atomic planes in the martensitic phase of Ni-Mn-Ga system. The EXAFS analysis also suggests the changes in hybridization of Ga-$p$ and Ni-$d$ orbitals associated with the local symmetry breaking upon undergoing martensitic transition.