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On the S(T) diagram of magnetocaloric materials with first-order transition: Kinetic and cyclic effects of Heusler alloys

Gottschall, Tino and Skokov, Konstantin P. and Burriel, Ramon and Gutfleisch, Oliver (2016):
On the S(T) diagram of magnetocaloric materials with first-order transition: Kinetic and cyclic effects of Heusler alloys.
In: Acta Materialia, PERGAMON-ELSEVIER SCIENCE LTD, pp. 1-8, 107, ISSN 13596454, [Online-Edition: http://dx.doi.org/10.1016/j.actamat.2016.01.052],
[Article]

Abstract

For magnetocaloric materials the total entropy diagram S(T) in different magnetic fields is of central importance. From such a plot the isothermal entropy change Delta S-T and the adiabatic temperature change Delta T-ad can be well-defined. Aim of this work is to investigate the reversible magnetocaloric effect of Heusler alloys under cycling in terms of the S(T) diagram. For this purpose we selected three different Heusler alloys of Ni-Mn-In with transition temperatures between 200 k and room temperature. The S(T) diagrams of the three materials cover all conceivable shapes and are therefore representative for inverse magnetocaloric Heusler alloys. First we comprehensively analyzed the magnetocaloric properties of this model system using calorimetry, magnetometry and direct measurements of the adiabatic temperature change Delta T-ad and subsequently combined those results into the S(T) diagram. It turns out that under certain measurement conditions significant discrepancies can appear. With the help of in-situ optical microscopy, this effect could be attributed to kinetic relaxation effects in the pure martensite phase before the actual Delta T-ad experiment. Furthermore we found that the S(T) diagram obtained under continuous heating and cooling fails to describe the reversible magnetocaloric properties of minor loops under cycling. Utilizing cyclic measurements of the adiabatic temperature change together with calorimetric data it is however possible to determine the reversible magnetic field induced entropy change Delta S-T in fast operation comparable to real device conditions which can be applied to every magnetocaloric material with a first-order transition. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Item Type: Article
Erschienen: 2016
Creators: Gottschall, Tino and Skokov, Konstantin P. and Burriel, Ramon and Gutfleisch, Oliver
Title: On the S(T) diagram of magnetocaloric materials with first-order transition: Kinetic and cyclic effects of Heusler alloys
Language: English
Abstract:

For magnetocaloric materials the total entropy diagram S(T) in different magnetic fields is of central importance. From such a plot the isothermal entropy change Delta S-T and the adiabatic temperature change Delta T-ad can be well-defined. Aim of this work is to investigate the reversible magnetocaloric effect of Heusler alloys under cycling in terms of the S(T) diagram. For this purpose we selected three different Heusler alloys of Ni-Mn-In with transition temperatures between 200 k and room temperature. The S(T) diagrams of the three materials cover all conceivable shapes and are therefore representative for inverse magnetocaloric Heusler alloys. First we comprehensively analyzed the magnetocaloric properties of this model system using calorimetry, magnetometry and direct measurements of the adiabatic temperature change Delta T-ad and subsequently combined those results into the S(T) diagram. It turns out that under certain measurement conditions significant discrepancies can appear. With the help of in-situ optical microscopy, this effect could be attributed to kinetic relaxation effects in the pure martensite phase before the actual Delta T-ad experiment. Furthermore we found that the S(T) diagram obtained under continuous heating and cooling fails to describe the reversible magnetocaloric properties of minor loops under cycling. Utilizing cyclic measurements of the adiabatic temperature change together with calorimetric data it is however possible to determine the reversible magnetic field induced entropy change Delta S-T in fast operation comparable to real device conditions which can be applied to every magnetocaloric material with a first-order transition. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Journal or Publication Title: Acta Materialia
Volume: 107
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Uncontrolled Keywords: Magnetocaloric effect, Heusler alloys, Calorimetry, Martensitic transition
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Functional Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 11 May 2016 12:42
Official URL: http://dx.doi.org/10.1016/j.actamat.2016.01.052
Identification Number: doi:10.1016/j.actamat.2016.01.052
Funders: This work was supported by DFG (Grant No. SPP 1599), European Community 7th Framework Program (Grant No. 310748 DRREAM), Spanish MINECO (Project MAT2013-44063-R) and DGA (Consolidated Group E100).
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