Relative Cooling Power Enhancement by Tuning Magneto-structural Stability in Ni-Mn-In Heusler Alloys

TL;DR

This study demonstrates how tuning the magneto-structural stability in Ni-Mn-In Heusler alloys enhances their relative cooling power, providing insights for designing efficient magnetocaloric materials.

Contribution

It introduces a method to improve RCP in Ni-Mn-In alloys by minor compositional adjustments affecting structural and magnetic stability.

Findings

Significant RCP enhancement achieved through compositional tuning.

RCP closely predicted by the ratio of $T_m$ to $T_C$.

Maximal entropy change observed despite RCP improvements.

Abstract

Off-stoichiometric Ni$_2$MnIn Heusler alloys have drawn recent attention due to their large magnetocaloric entropy change associated with the first-order magneto-structural transition. Here we present crystal structural, calorimetric and magnetic studies of three compositions. Temperature-dependent X-ray diffraction shows clear structural transition from a 6M modulated monoclinic to a L2$_1$ cubic. A significant enhancement of relative cooling power (RCP) was achieved by tuning the magnetic and structural stability through minor compositional changes, with the measured results quantitatively close to the prediction as a function of the ratio between the martensitic transition ($T_m$) temperature and austenite Curie temperature ($T_C$) although the maximal magnetic induced entropy change ($\Delta S_{max}$) reduction is observed in the same time. The results provided an evaluation guideline of RCPs as well as magnetic-induced entropy change in designing practical active materials.