Lattice strain accommodation and absence of pre-transition phases in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$

TL;DR

This study investigates the lattice strain accommodation in Ni-Mn-In Heusler alloys, revealing the absence of pre-transition phases and the conditions under which martensitic transformation occurs.

Contribution

It demonstrates that the ferromagnetic cubic structure can accommodate lattice strain without pre-transition phases, and identifies the critical composition for martensitic transformation.

Findings

No pre-transition phases like strain glass are observed.

Lattice strain is accommodated by the cubic structure.

Martensitic transformation occurs beyond x=8.75 despite magnetic clustering.

Abstract

The stoichiometric Ni$_{50}$Mn$_{25}$In$_{25}$ Heusler alloy transforms from a stable ferromagnetic austenitic ground state to an incommensurate modulated martensitic ground state with a progressive replacement of In with Mn without any pre-transition phases. The absence of pre-transition phases like strain glass in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$ alloys is explained to be the ability of the ferromagnetic cubic structure to accommodate the lattice strain caused by atomic size differences of In and Mn atoms. Beyond the critical value of $x$ = 8.75, the alloys undergo martensitic transformation despite the formation of ferromagnetic and antiferromagnetic clusters and the appearance of a super spin glass state.