  The thermodynamic stability of the premartensite (PM) phase has been a topic
of extensive investigation in shape memory alloys as it affects the main
martensite phase transition and the related physical properties. In general,
the PM phase is stable over a rather narrow temperature-composition range. We
present here evidence for chemical pressure induced suppression of the main
martensite transition and stabilization of the PM phase over a very wide
temperature range from 300 K to around 5 K in a magnetic shape memory alloy
(MSMA) Ni50Mn34In16 using magnetic susceptibility, synchrotron X-ray powder
diffraction (SXRPD) studies and first-principles calculations. The
ac-susceptibility studies show a highly skewed and smeared peak around 300 K
without any further transition up to the lowest temperature of our measurement
(5 K) for around 5% Al substitution. The temperature evolution of the SXRPD
patterns confirms the appearance of the PM phase related satellite peaks at and
below 300 K without any splitting of the main austenite (220) peak showing
preserved cubic symmetry. This is in marked contrast to the temperature
evolution of the SXRPD patterns of the martensite phase of the Al free as well
as around 3% Al substituted compositions where the austenite (220) peak shows a
clear splitting due to Bain distortion/symmetry breaking transition. Our
theoretical calculations support the experimental findings and reveal that the
substitution at the In site by a smaller size atom, like Al, can stabilize the
PM phase with preserved cubic symmetry. Our results demonstrate that
Al-substituted Ni-Mn-In MSMAs provide an ideal platform for investigating the
physics of various phenomena related to the PM state.
