Robust evidence for the stabilization of the premartensite phase in Ni-Mn-In magnetic shape memory alloys by chemical pressure

TL;DR

This study demonstrates that chemical pressure via Al substitution stabilizes the premartensite phase in Ni-Mn-In magnetic shape memory alloys over a wide temperature range, affecting phase transitions and symmetry.

Contribution

It provides experimental and theoretical evidence that Al substitution stabilizes the premartensite phase by suppressing the martensite transition and preserving cubic symmetry.

Findings

Al substitution stabilizes premartensite phase from 300 K to 5 K.

No splitting of austenite peak indicates preserved cubic symmetry.

Theoretical calculations confirm stabilization mechanism via chemical pressure.

Abstract

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.