Long-Range Atomic Order and Entropy Change at the Martensitic Transformation in a Ni-Mn-In-Co Metamagnetic Shape Memory Alloy

Vicente Sánchez-Alarcos,Vicente Recarte,Eduard Cesari,José Rodríguez-Velamazán,José Pérez-Landazábal

doi:10.3390/e16052756

Abstract

The influence of the atomic order on the martensitic transformation entropy change has been studied in a Ni-Mn-In-Co metamagnetic shape memory alloy through the evolution of the transformation temperatures under high-temperature quenching and post-quench annealing thermal treatments. It is confirmed that the entropy change evolves as a consequence of the variations on the degree of L21 atomic order brought by thermal treatments, though, contrary to what occurs in ternary Ni-Mn-In, post-quench aging appears to be the most effective way to modify the transformation entropy in Ni-Mn-In-Co. It is also shown that any entropy change value between around 40 and 5 J/kgK can be achieved in a controllable way for a single alloy under the appropriate aging treatment, thus bringing out the possibility of properly tune the magnetocaloric effect.

Highlights

It is confirmed that the entropy change evolves as a consequence of the variations on the degree of L21 atomic order brought by thermal treatments, though, contrary to what occurs in ternary Ni-Mn-In, post-quench aging appears as the most effective way to modify the transformation entropy in Ni-Mn-In-Co
It is shown that any entropy change value between around 40 and 5 J/kgK can be achieved in a controllable way for a single alloy under the appropriate aging treatment, bringing out the possibility of properly tune the magnetocaloric effect
From the latent heat estimated from the area bellow the peaks in Figure 1, Q, the corresponding entropy change at the martensitic transformation (MT) has been calculated as ΔS = Q/Tm

Summary

Introduction

Ni-Mn-based Heusler alloys exhibiting both long-range magnetic ordering and thermoelastic martensitic transformation (MT) have been intensively investigated in recent years, from both fundamental and applied points of view, due to the unique properties they show linked to the occurrence of a first-order martensitic transformation (MT) between magnetically ordered phases [1]. The magnetic contribution, and the entropy change at the MT, can be modified by the application of an external magnetic field [17] and, taking into account that the magnetic moment depends on the configurational ordering of the magnetic atoms in the crystal lattice, by the variation of the long-range atomic order In this last respect, it has been recently shown that, for a given alloy composition, the atomic order can be modified in Ni-Mn-In alloys by means of different thermal treatments [18,19]. This leads to an increase of ΔM at the MT which favors larger magnetically-induced shifts of the transformation temperatures and results in a higher associated magnetocaloric effect [25] In these quaternary alloys, the entropy change at the transformation, ΔS, strongly varies with the degree of atomic order, which can be tailored by means of the thermal treatment [26]. It is shown that any entropy change value between around 40 and 5 J/kgK can be achieved in a controllable way for a single alloy under the appropriate aging treatment, bringing out the possibility of properly tune the magnetocaloric effect

Experimental Section

Results and Discussion

Conclusions