Abstract:
The interplay between electronic structure and lattice degrees of freedom governs martensitic transformations in Ni-Mn-based Heusler alloys, yet their relative contributions remain difficult to disentangle. Here, we address this issue through a systematic investigation of Ni sub(2)Mn sub(1.5)Ga sub(0.5-x)In sub(x) (0 less than or equal to x less than or equal to 0.5), where isoelectronic substitution of In for Ga enables isolation of lattice effects at nearly constant valence electron concentration (e/a approximately equal to 8). A pronounced and monotonic decrease in the martensitic transformation temperature (T sub(M)) is observed with increasing In content, despite negligible variation in e/a, indicating a non-electronic origin of the transformation suppression. On the other hand, a direct correlation between T sub(M) and lattice expansion and the bond-length difference Delta R = (R sub(Ni-Z)- R sub(Ni-Mn)) establishes local structural distortions as a key control parameter. These results are interpreted within a strain accommodation framework, wherein lattice expansion induced by larger In atoms progressively relieves internal strain, thereby reducing the elastic energy difference between austenite and martensite phases and suppressing the transformation. Magnetization measurements further indicate the emergence of frustrated magnetic states arising from competing exchange interactions in a structurally heterogeneous environment. These findings demonstrate that lattice-driven effects can dominate martensitic phase stability independently of electronic concentration and provide a pathway for tuning functional properties in Heusler alloys via controlled manipulation of local structure and strain.
