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Magnetic and magnetocaloric properties of the Co2-xMn B system by experiment and density functional theory

Ener, Semih and Fries, Maximilian and Hammerath, Franziska and Opahle, Ingo and Simon, Eszter and Fritsch, Patrizia and Wurmehl, Sabine and Zhang, Hongbin and Gutfleisch, Oliver (2019):
Magnetic and magnetocaloric properties of the Co2-xMn B system by experiment and density functional theory.
In: Acta Materialia, Elsevier Science Publishing, pp. 270-277, 165, ISSN 13596454, DOI: 10.1016/j.actamat.2018.11.034, [Online-Edition: https://doi.org/10.1016/j.actamat.2018.11.034],
[Article]

Abstract

The Co2B system shows a significant magnetovolume effect around its Curie temperature which makes it potentially attractive for magnetocaloric applications or thermomagnetic power generation, as a large coupling between the lattice and spin degrees of freedom is expected. We report on the synthesis of a series of Co2-xMnxB alloys and the investigation of their properties. The structural analysis indicates a single phase behavior up to x = 0.8 with no structural symmetry changes throughout the series. Measurements of both, macroscopic and local magnetic properties, reveal an anomalous behavior of the spontaneous magnetization, Curie temperature, and element-specific magnetic moments as a function of manganese concentration. The elemental contributions to the magnetization are analyzed using nuclear magnetic resonance (NMR) studies. Density functional theory (DFT) calculations guide us in the understanding of the origin of the observed anomaly, which is due to a complex magnetic coupling behavior between Mn atoms, which significantly affects the corresponding exchange interactions. The magnetocaloric properties of the Co2-xMnxB alloys show that the maximum entropy change peak temperature can be shifted between room temperature and 450 K upon variation of the manganese concentration without significant impact on the magnetocaloric response. The highest entropy change of -1.37 Jkg(-1)K(-1) at 442 K is obtained for x = 0.1 for a field change of 2 T. This value is, however, quite low for any possible magnetocaloric or thermomagnetic power generation applications. Nevertheless, the good agreement between the advanced characterization and theory gives a deeper understanding of the Co2-xMnxB material system which can in the future be extended to other systems. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Item Type: Article
Erschienen: 2019
Creators: Ener, Semih and Fries, Maximilian and Hammerath, Franziska and Opahle, Ingo and Simon, Eszter and Fritsch, Patrizia and Wurmehl, Sabine and Zhang, Hongbin and Gutfleisch, Oliver
Title: Magnetic and magnetocaloric properties of the Co2-xMn B system by experiment and density functional theory
Language: English
Abstract:

The Co2B system shows a significant magnetovolume effect around its Curie temperature which makes it potentially attractive for magnetocaloric applications or thermomagnetic power generation, as a large coupling between the lattice and spin degrees of freedom is expected. We report on the synthesis of a series of Co2-xMnxB alloys and the investigation of their properties. The structural analysis indicates a single phase behavior up to x = 0.8 with no structural symmetry changes throughout the series. Measurements of both, macroscopic and local magnetic properties, reveal an anomalous behavior of the spontaneous magnetization, Curie temperature, and element-specific magnetic moments as a function of manganese concentration. The elemental contributions to the magnetization are analyzed using nuclear magnetic resonance (NMR) studies. Density functional theory (DFT) calculations guide us in the understanding of the origin of the observed anomaly, which is due to a complex magnetic coupling behavior between Mn atoms, which significantly affects the corresponding exchange interactions. The magnetocaloric properties of the Co2-xMnxB alloys show that the maximum entropy change peak temperature can be shifted between room temperature and 450 K upon variation of the manganese concentration without significant impact on the magnetocaloric response. The highest entropy change of -1.37 Jkg(-1)K(-1) at 442 K is obtained for x = 0.1 for a field change of 2 T. This value is, however, quite low for any possible magnetocaloric or thermomagnetic power generation applications. Nevertheless, the good agreement between the advanced characterization and theory gives a deeper understanding of the Co2-xMnxB material system which can in the future be extended to other systems. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Journal or Publication Title: Acta Materialia
Volume: 165
Publisher: Elsevier Science Publishing
Uncontrolled Keywords: Monoboride, DFT, Entropy, Magnetocaloric effect, Co2B, NMR
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
11 Department of Materials and Earth Sciences > Material Science > Theory of Magnetic Materials
Date Deposited: 28 Feb 2019 07:36
DOI: 10.1016/j.actamat.2018.11.034
Official URL: https://doi.org/10.1016/j.actamat.2018.11.034
Funders: The research was funded by the European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement number 310748 (DRREAM)., The financial support by the DFG (Grant No. SPP 1599, WU595/3-3, WU595/11, and WU595/14-1) and the German federal state of Hessen through its excellence programme LOEWE "RESPONSE" are acknowledged.
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