Impact of swaps on Mössbauer characteristics of Ni₂MnSn: an experimental and quantum-mechanical study

We report on a combined experimental and theoretical study of stoichiometric Heusler-structure Ni₂MnSn. Our detected Mössbauer spectrum of Sn atoms can be fitted as a combination of four components. As only a single component is expected in the defect-free Ni₂MnSn, we have performed quantum-mechanical calculations of Ni₂MnSn with selected point defects, in particular, all three fundamental types of swaps (Mn–Ni, Mn–Sn and Ni–Sn). Our phonon and elasticity calculations indicate that the swaps result in (i) magnitudes of local magnetic moments of Sn atoms within four ranges of values and (ii) mean square displacements of Sn atoms falling within four intervals of values. Further, we used calculations of phonons and elastic properties to assess mechanical, dynamical and thermodynamic stability of swap-containing states. Our results indicate that a majority of the studied swaps is reducing the stability of Ni₂MnSn and need to be stabilized by the surrounding matrix.