Entropy change at the martensitic transformation in ferromagnetic shape memory alloys Ni_{2+x}Mn_{1-x}Ga

TL;DR

This study investigates the entropy change during the martensitic transformation in Ni-Mn-Ga ferromagnetic shape memory alloys, revealing how Ni content influences entropy and the role of magnetic contributions.

Contribution

It provides new experimental insights into how Ni excess affects entropy change and modulation in Ni-Mn-Ga alloys during martensitic transformation.

Findings

Entropy change increases with Ni content.

Magnetic contributions significantly affect entropy change.

Modulation changes cause discontinuities in entropy dependence.

Abstract

The entropy change $\Delta S$ between the high-temperature cubic phase and the low-temperature tetragonally-based martensitic phase of Ni$_{2+x}$Mn$_{1-x}$Ga ($x = 0 - 0.20$) alloys was studied. The experimental results obtained indicate that $\Delta S$ in the Ni$_{2+x}$Mn$_{1-x}$Ga alloys increases with the Ni excess $x$. The increase of $\Delta S$ is presumably accounted for by an increase of magnetic contribution to the entropy change. It is suggested that the change in modulation of the martensitic phase of Ni$_{2+x}$Mn$_{1-x}$Ga results in discontinuity of the composition dependence of $\Delta S$.