Failure of the Maxwell relation for the quantification of caloric effects in ferroic materials

0377247 - FZÚ 2013 DE eng E - Elektronický dokument
Niemann, R. - Heczko, Oleg - Schultz, L. - Fähler, S.
Failure of the Maxwell relation for the quantification of caloric effects in ferroic materials.
2011
Grant CEP: GA ČR(CZ) GAP107/11/0391
Výzkumný záměr: CEZ:AV0Z10100520
Klíčová slova: magnetocaloric effect * martensitic transformation * Ni-Mn-Ga * entropy change
Kód oboru RIV: BM - Fyzika pevných látek a magnetismus
http://arxiv.org/ftp/arxiv/papers/1110/1110.3617.pdf

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. We report the fundamental failure of this approach. We analyze exemplarily the Ni-Mn-Ga magnetic shape memory alloy. An applied field results in magnetically induced reorientation of martensitic variants, which form during the phase transformation. This results in a spurious magnetocaloric effect, which only disappears when repeating the measurement a second time. This failure is universal as the vector character of the applied field is not considered in the common scalar evaluation of a Maxwell relation.
Trvalý link: http://hdl.handle.net/11104/0209455