Ultraslow calorimetric studies of the martensitic transformation of NiFeGa alloys: detection and analysis of avalanche phenomena

TL;DR

This study investigates the ultraslow calorimetric behavior of NiFeGa alloys during martensitic transformation, revealing avalanche phenomena and their statistical properties, which enhances understanding of phase transition dynamics in shape memory alloys.

Contribution

It provides the first detailed analysis of calorimetric avalanches in NiFeGa alloys at ultraslow heating rates, including their statistical distribution and asymmetry in transformation.

Findings

Detection of calorimetric avalanches during martensitic transformation.

Avalanche size distribution follows a power law with exponential cutoff.

Asymmetry observed between direct and reverse transformation energies.

Abstract

We study the thermal properties of a bulk Ni55Fe19Ga26 Heusler alloy in a conduction calorimeter. At slow heating and cooling rates (1K/h), we compare as-cast and annealed samples. We report a smaller thermal hysteresis after the thermal treatment due to the stabilization of the 14M modulated structure in the martensite phase. In ultraslow experiments (40mK/h), we detect and analyze the calorimetric avalanches associated with the direct and reverse martensitic transformation from cubic to 14M phase. This reveals a distribution of events characterized by a power law with exponential cutoff $p(u) \propto u^{-\varepsilon}\exp(-u/\xi)$ where $\varepsilon\sim 2$ and damping energies $\xi=370$uJ (direct) and $\xi=27$uJ (reverse) that characterize the asymmetry of the transformation.