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arXiv · 1110.3617

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

Robert Niemann·Oleg Heczko·Ludwig Schultz·Sebastian Fähler
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Abstract

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.

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Robert Niemann, Oleg Heczko, Ludwig Schultz, Sebastian Fähler. 2011-10-17. Failure of the Maxwell relation for the quantification of caloric effects in ferroic materials. https://doi.org/10.1016/j.ijrefrig.2013.07.029

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