Simultaneous direct measurements of conventional and inverse magnetocaloric effects in Ni–Mn-based Heusler alloys using lock-in thermography technique

Rajkumar Modak,Ryo Iguchi,Ken-Ichi Uchida,Hossein Sepehri-Amin,Asuka Miura

doi:10.1063/5.0005865

Abstract

The second-order conventional and first-order inverse magnetocaloric effects (MCEs) in Ni–Mn-based quaternary Heusler alloys have been systematically investigated by means of the lock-in thermography technique, which enables the direct measurement of the MCE-induced temperature change in a periodic magnetic field. Through systematic measurements of the temperature dependence of the MCE signals, the tuning of the conventional and inverse MCEs with temperature for the same Heusler alloys has been demonstrated, where the phase transitions responsible for the MCEs are clearly distinguished. The lock-in thermography measurements show that some Ni–Mn-based Heusler alloys exhibit much smaller temperature changes due to the inverse MCEs in the periodic field as compared to the conventional MCEs, even though they exhibit a larger magnetic entropy change across the first-order transition responsible for the inverse MCEs. We discuss the origin of this behavior in terms of the field-induced entropy change and thermal hysteresis of the alloys. These findings will be useful not only in accelerating the optimization of inverse MCE materials but also in understanding the mechanism of the MCEs.

Highlights

By means of thermal imaging based on the lock-in thermography (LIT), we performed simultaneous direct measurements of the second-order conventional and first-order inverse magnetocaloric effects (MCEs) in a periodic magnetic field in the Ni–Mn-based Heusler alloys, which are believed to be promising candidates for inverse MCE applications
The LIT allows us to visualize the temperature modulation induced by the conventional and inverse MCEs in the alloys, which is due to the secondorder magnetic and first-order magneto-structural phase transitions, respectively
We found that the magnitude of the inverse-MCEinduced temperature modulation in Ni41.1Mn39.9Co5.5Sb13.5 and Ni46.3Mn36.6Si1.4In15.7 in a periodic magnetic field is tiny, the alloys exhibit large isothermal magnetic entropy change, indicating that the magnetization measurements combined with the Maxwell thermodynamic relation cannot predict the actual performance of the inverse MCE materials

Summary

INTRODUCTION

Refrigeration technology based on magnetocaloric effects (MCEs) has been proposed long ago after the successful demonstration of a magnetic refrigerator to reach sub-Kelvin temperatures by Giauque and MacDougall in 1933.1 The primary focus of the magnetic refrigeration was to reach very low temperatures, which cannot be realized by gas-based refrigeration alone.[1,2] In contrast, the concept of room-temperature refrigeration based on MCEs came into play after Brown’s proposal in 1976.3 The whole scenario changed after the discovery of the room-temperature giant magnetocaloric effect in a Gd5Si2Ge2 alloy in 1997.4 Since this discovery, intensive research has been carried out to realize the MCE-based refrigerator as an environment-friendly and energy-efficient alternative for conventional gas-based refrigeration, which involves greenhouse gases.[5]. Some attempts have been made to directly measure ΔTad due to the inverse MCEs in Heusler alloys[17–29] and other materials[24,27,30–32] using various experimental setups These methods are applicable only to one-by-one measurements, which limit the throughput of material searching. The phase transition temperature in these alloys can be tuned over a wide temperature range with change in the composition According to these factors, these alloys are believed to be promising for the development of a refrigerator based on the inverse MCEs. systematic direct measurements of ΔTad for the Ni–Mn-based Heusler alloys are necessary. To confirm the actual performance of the conventional and inverse MCEs in these alloys, we performed the LIT-based direct measurements of magnetic-field-induced temperature modulation in a periodic magnetic field, which is the real operating condition in a magnetocaloric refrigerator

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSION

CONCLUSION