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

TL;DR

This study investigates the complex phase transitions in a Ni-Mn-In shape memory alloy using calorimetric, magnetic, and acoustic methods, revealing detailed thermomagnetic behavior, avalanche dynamics, and critical phenomena.

Contribution

It provides a detailed thermo-magnetic characterization of overlapping phase transitions, including latent heat, avalanche dynamics, and critical exponents, advancing understanding of Ni-Mn-In alloys.

Findings

Latent heat of transition: 7.21 kJ/kg

Avalanche energy distribution follows a power law with exponent ~2

Critical exponent for magnetic transition: ~0.09

Abstract

The partially overlapped ferroelastic/martensitic and para-ferromagnetic phase transitions of a Ni$_{50.53}$Mn${33.65}$In$_{15.82}$ 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 ($\sim2.5$K) to discriminate the latent heat contribution $\Delta$Ht = 7.21(15) kJ/kg and the specific heat contribution $\Delta$Hc = 216(1) J/kg 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 avalanches 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 $\epsilon\sim2$ 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 $\sim 311$K has been studied from the behavior of the specific heat. A critical exponent $\alpha\sim0.09$ 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.