Martensitic transition and magnetoresistance in a Cu-Al-Mn shape memory alloy. Influence of aging

TL;DR

This study investigates how aging affects the magnetic, electric, and thermodynamic properties of a Cu-Al-Mn shape-memory alloy, revealing the influence of Mn-rich clusters on magnetoresistance and phase transformation behavior.

Contribution

It provides new insights into the effects of aging within the miscibility gap on the properties and phase transitions of Cu-Al-Mn shape-memory alloys, highlighting the role of Mn-rich clusters.

Findings

Negative magnetoresistance correlates with magnetization squared in different phases.

Aging decreases entropy change between phases due to increased Mn-rich domains.

Magnetic field has negligible effect on entropy change during phase transition.

Abstract

We have studied the effect of ageing within the miscibility gap on the electric, magnetic and thermodynamic properties of a non-stoichiometric Heusler Cu-Al-Mn shape-memory alloy, which undergoes a martensitic transition from a $bcc$-based ($\beta$-phase) towards a close-packed structure ($M$-phase). Negative magnetoresistance which shows an almost linear dependence on the square of magnetization with different slopes in the $M$- and $\beta$-phases, was observed. This magnetoresistive effect has been associated with the existence of Mn-rich clusters with the Cu$_2$AlMn-structure. The effect of an applied magnetic field on the martensitic transition has also been studied. The entropy change between the $\beta$- and $M$-phases shows negligible dependence on the magnetic field but it decreases significantly with annealing time within the miscibility gap. Such a decrease is due to the increasing amount of Cu$_2$MnAl-rich domains that do not transform martensitically.