Experimentally correlating thermal hysteresis and phase compatibility in multifunctional Heusler alloys

TL;DR

This study investigates how phase compatibility influences thermal hysteresis in Ni2Mn1-xCuxGa0.84Al0.16 Heusler alloys, demonstrating that improved compatibility reduces hysteresis significantly, which is crucial for their cyclical applications.

Contribution

The paper provides experimental evidence linking phase compatibility, quantified by lambda2, to hysteresis reduction in Heusler alloys, offering new strategies for optimizing their functional properties.

Findings

Thermal hysteresis decreases by ~60% with Cu content increase from x=0.10 to 0.25.

Better phase compatibility (lambda2 closer to 1) correlates with minimal hysteresis.

Hysteresis valley-like behavior is observed across various related alloys.

Abstract

Thermal hysteresis is recognized as one of the main drawbacks for cyclical applications of magnetocaloric and ferromagnetic shape memory materials with first order transformations. As such, the challenge is to develop strategies that improve the compatibility between the phases involved in the transitions and study its influence on thermal hysteresis. With this purpose, we explore the thermal, structural and magnetic properties of the Ni2Mn1-xCuxGa0.84Al0.16 Heusler alloys. The alloys present a thermal hysteresis reduction of ~60% when the Cu content in the compound varies from x = 0.10 to x = 0.25, with a minimum hysteresis width of 6 K being achieved. We applied the geometric non-linear theory of martensite to address the phase compatibility, quantified by the parameter lambda2, the middle eigenvalue of the transformation stretch tensor, and found that the minimum of hysteresis is associated with a better crystallographic compatibility (lambda2 closer to 1) between the austenite and martensite phases. In addition, we show that the valley-like properties of hysteresis found in the Ni2Mn1-xCuxGa0.84Al0.16 compounds is present in several other alloys in the literature. These results provide new pathways to understand as well as to masters the phase compatibility and ultimately achieve a low thermal hysteresis in multifunctional Heusler alloys.