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- ItemLow-Temperature Magnetothermodynamics Performance of Tb1-xErxNi2 Laves-Phases Compounds for Designing Composite Refrigerants(Basel : MDPI, 2022) Ćwik, Jacek; Koshkid’ko, Yurii; Nenkov, Konstantin; Tereshina-Chitrova, Evgenia; Weise, Bruno; Kowalska, KarolinaIn this paper, the results of heat capacity measurements performed on the polycrystalline Tb1-xErxNi2 intermetallic compounds with x = 0.25, 0.5 and 0.75 are presented. The Debye temperatures and lattice contributions as well as the magnetic part of the heat capacity were determined and analyzed. The heat capacity measurements reveal that the substitution of Tb atoms for Er atoms leads to a linear reduction of the Curie temperatures in the investigated compounds. The ordering temperatures decrease from 28.3 K for Tb0.25Er0.75Ni2 to 12.9 K for Tb0.75Er0.25Ni2. Heat capacity measurements enabled us to calculate with good approximation the isothermal magnetic entropy ΔSmag and adiabatic temperature changes ΔTad for Tb1-xErxNi2, for the magnetic field value equal to 1 T and 2 T. The optimal molar ratios of individual Tb0.75Er0.25Ni2, Tb0.5Er0.5Ni2 and Tb0.25Er0.75Ni2 components in the final composite were theoretically determined. According to the obtained results, the investigated composites make promising candidates that can find their application as an active body in a magnetic refrigerator performing an Ericsson cycle at low temperatures. Moreover, for the Tb0.5Er0.5Ni2 compound, direct measurements of adiabatic temperature change in the vicinity of the Curie temperature in the magnetic field up to 14 T were performed. The obtained high-field results are compared to the data for the parent TbNi2 and ErNi2 compounds, and their magnetocaloric properties near the Curie temperature are analyzed in the framework of the Landau theory for the second-order phase transitions.
- ItemRole of disorder when upscaling magnetocaloric Ni-Co-Mn-Al Heusler alloys from thin films to ribbons(London : Nature Publishing Group, 2018) Weise, B.; Dutta, B.; Teichert, N.; Hütten, A.; Hickel, T.; Waske, A.Research in functional magnetic materials often employs thin films as model systems for finding new chemical compositions with promising properties. However, the scale-up of thin films towards bulk-like structures is challenging, since the material synthesis conditions are entirely different for thin films and e.g. rapid quenching methods. As one of the consequences, the type and degree of order in thin films and melt-spun ribbons are usually different, leading to different magnetic properties. In this work, using the example of magnetocaloric Ni-Co-Mn-Al melt-spun ribbons and thin films, we show that the excellent functional properties of the films can be reproduced also in ribbons, if an appropriate heat treatment is applied, that installs the right degree of order in the ribbons. We show that some chemical disorder is needed to get a pronounced and sharp martensitic transition. Increasing the order with annealing improves the magnetic properties only up to a point where selected types of disorder survive, which in turn compromise the magnetic properties. These findings allow us to understand the impact of the type and degree of disorder on the functional properties, paving the way for a faster transfer of combinatorial thin film research towards bulk-like materials for magnetic Heusler alloys.
- ItemIntrinsische Eigenschaften ferromagnetischer Phasen : Magnetwerkstoffe ; Abschlussbericht(Dresden : Leibniz-Institut für Festkörper- und Werkstoffforschung, 2000) Handstein, Axel; Müller, Karl-Hartmut[no abstract available]