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Microstructural origin of hysteresis in Ni-Mn-In based magnetocaloric compounds

Sepehri-Amin, H. and Taubel, A. and Ohkubo, T. and Skokov, K. P. and Gutfleisch, O. and Hono, K. (2018):
Microstructural origin of hysteresis in Ni-Mn-In based magnetocaloric compounds.
In: Acta Materialia, Elsevier Science Publishing, pp. 342-349, 147, ISSN 13596454, DOI: 10.1016/j.actamat.2018.01.044, [Online-Edition: https://doi.org/10.1016/j.actamat.2018.01.044],
[Article]

Abstract

Microstructures of magnetocaloric Ni-Mn-In-based Heusler alloys, Ni50.2Mn35.0In14.8 and Ni46.1Mn37.9Fe3.0In13.0, were studied to understand the origin of a large difference in thermal hysteresis in these two alloys. In-situ transmission electron microscopy (TEM) observation showed that the Fe containing sample with a large hysteresis shows a discontinuous phase transition due to the existence of nano-scale Fe-rich bcc phase, along with Fe-lean B2 and L21 phases in the austenite state. The Fe-free sample with a low hysteresis shows a uniform phase transition from martensite to austenite initiated by the nucleation of austenite at the twin boundaries. Ni segregation was found at the twin boundaries of the low hysteresis sample that is considered to facilitate the nucleation of the austenite. The phase transition progresses by the growth of the nucleated austenite to the neighboring twins. 5M and 7M modulated martensites in the low hysteresis sample give rise to a slight difference in the phase transition temperatures in the twin bands contributing to the small hysteresis of 4.4 K in the Fe-free sample. Based on these results, we conclude that to minimize the thermal hysteresis of the Ni-Mn-In based magnetocaloric compounds, one of the key factors is to achieve a uniform composition and crystal structure in the alloy.

Item Type: Article
Erschienen: 2018
Creators: Sepehri-Amin, H. and Taubel, A. and Ohkubo, T. and Skokov, K. P. and Gutfleisch, O. and Hono, K.
Title: Microstructural origin of hysteresis in Ni-Mn-In based magnetocaloric compounds
Language: English
Abstract:

Microstructures of magnetocaloric Ni-Mn-In-based Heusler alloys, Ni50.2Mn35.0In14.8 and Ni46.1Mn37.9Fe3.0In13.0, were studied to understand the origin of a large difference in thermal hysteresis in these two alloys. In-situ transmission electron microscopy (TEM) observation showed that the Fe containing sample with a large hysteresis shows a discontinuous phase transition due to the existence of nano-scale Fe-rich bcc phase, along with Fe-lean B2 and L21 phases in the austenite state. The Fe-free sample with a low hysteresis shows a uniform phase transition from martensite to austenite initiated by the nucleation of austenite at the twin boundaries. Ni segregation was found at the twin boundaries of the low hysteresis sample that is considered to facilitate the nucleation of the austenite. The phase transition progresses by the growth of the nucleated austenite to the neighboring twins. 5M and 7M modulated martensites in the low hysteresis sample give rise to a slight difference in the phase transition temperatures in the twin bands contributing to the small hysteresis of 4.4 K in the Fe-free sample. Based on these results, we conclude that to minimize the thermal hysteresis of the Ni-Mn-In based magnetocaloric compounds, one of the key factors is to achieve a uniform composition and crystal structure in the alloy.

Journal or Publication Title: Acta Materialia
Volume: 147
Publisher: Elsevier Science Publishing
Uncontrolled Keywords: Hysteresis, Magnetocaloric, Heusler alloys, Microstructure, In-situ TEM
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Functional Materials
Date Deposited: 12 Mar 2018 09:54
DOI: 10.1016/j.actamat.2018.01.044
Official URL: https://doi.org/10.1016/j.actamat.2018.01.044
Funders: This work was in part supported by LG electronics., OG and AT acknowledge the support by DFG SPP 1599 and helpful discussion with Max Fries and Tino Gottschall.
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