Direct Measure of Giant Magnetocaloric Entropy Contributions in Ni-Mn-In

TL;DR

This study measures the entropy contributions in Ni-Mn-In alloys related to magnetocaloric effects, revealing the role of magneto-elastic coupling and magnetic order in the phase transitions.

Contribution

It provides the first direct calorimetric and magnetic measurement of entropy changes in Ni-Mn-In alloys, clarifying the influence of magnetic order and magneto-elastic coupling.

Findings

Large entropy change due to magneto-elastic coupling in compositions without ferromagnetic order.

Agreement of a molecular field model with experimental data across compositions.

Identification of the maximum field-induced entropy change for giant magnetocaloric effect.

Abstract

Off-stoichiometric alloys based on Ni 2 MnIn have drawn attention due to the coupled first order magnetic and structural transformations, and the large magnetocaloric entropy associated with the transformations. Here we describe calorimetric and magnetic studies of four compositions. The results provide a direct measure of entropy changes contributions including at the first-order phase transitions, and thereby a determination of the maximum field-induced entropy change corresponding to the giant magnetocaloric effect. We find a large excess entropy change, attributed to magneto-elastic coupling, but only in compositions with no ferromagnetic order in the high-temperature austenite phase. Furthermore, a molecular field model corresponding to antiferromagnetism of the low-temperature phases is in good agreement, and nearly independent of composition, despite significant differences in overall magnetic response of these materials.