期刊
INTERNATIONAL JOURNAL OF REFRIGERATION-REVUE INTERNATIONALE DU FROID
卷 37, 期 -, 页码 281-288出版社
ELSEVIER SCI LTD
DOI: 10.1016/j.ijrefrig.2013.07.029
关键词
Magnetocaloric; Shape memory alloys; Multiferroic; Ni-Mn-Ga; Maxwell relation
资金
- DFG [SPP 1239, FA 453/7, SPP 1599, FA 453/11-1]
- Academy of Sciences of the Czech Republic
- CSF [107/11/0391]
Giant caloric effects were reported in elasto-, electro- and magnetocaloric materials near phase transformations. Commonly, their entropy change is indirectly evaluated by a Maxwell relation. Additionally to the well-known spurious colossal results near first-order phase transitions and limitations in the presence of magnetic domains, we report the fundamental failure of this approach for materials that show structural reorientations in external fields. We analyze exemplarily the magnetic shape memory alloy Ni-Mn-Ga. Application of a magnetic field causes magnetically induced reorientation of the crystal structure in the martensite phase. This results in a spurious inverse magnetocaloric effect that disappears when the measurement procedure is repeated. This failure is universal as the vector character of the applied field is not considered in the common scalar evaluation of a Maxwell relation. (C) 2013 Elsevier Ltd and IIR. All rights reserved.
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