Thermo-magnetic characterization of phase transitions in a Ni-Mn-In metamagnetic shape memory alloy

The partially overlapped ferroelastic/martensitic and para-ferromagnetic phase transitions of a Ni50.53Mn33.65In15.82 metamagnetic shape memory alloy have been studied from calorimetric, magnetic and acoustic emission measurement. We have taken advantage of the existence of thermal hysteresis of the first order ferroelastic/martensitic phase transition (similar to 2.5 K) to discriminate the latent heat contribution Delta H-t = 7.21(15)kJkg(-1) and the specific heat contribution Delta H-c = 216(1)Jkg(-1) to the total excess enthalpy of the phase transition. The specific heat was found to follow a step-like behavior at this phase transition. The intermittent dynamics of the ferroelastic/martensitic transition has been characterized as a series of avalaches detected both from acoustic emission and calorimetric measurements. The energy distribution of these avalanche events was found to follow a power law with a characteristic energy exponent epsilon congruent to 2 which is in agreement with the expected value for a system undergoing a symmetry change from cubic to monoclinic. Finally, the critical behavior of the para-ferromagnetic austenite phase transition that takes place at similar to 311 K has been studied from the behavior of the specific heat. A critical exponent alpha congruent to 0.09 has been obtained, which has been shown to be in agreement with previous values reported for Ni-Mn-Ga alloys but different from the critical divergence reported for pure Ni. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

The study investigated the ferroelastic/martensitic and para-ferromagnetic phase transitions of a Ni50.53Mn33.65In15.82 metamagnetic shape memory alloy through calorimetric, magnetic, and acoustic emission measurements. The research focused on distinguishing the latent heat contribution and specific heat contribution to the total excess enthalpy of the phase transition, revealing step-like behavior in specific heat and intermittent dynamics of the ferroelastic/martensitic transition. Critical behavior of the para-ferromagnetic austenite phase transition was also studied, showing a critical exponent in agreement with previous findings for Ni-Mn-Ga alloys.