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

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.

8 pages, 4 figures

References in corpus (4)

• Giant electrocaloric effect in thin film Pb Zr_0.95 Ti_0.05 O_3
• Elastocaloric effect associated with the martensitic transition in shape-memory alloys
• Giant entropy change at the co-occurrence of structural and magnetic transitions in the Ni2.19Mn0.81Ga Heusler alloy
• Magnetic shape-memory effects in La2-xSrxCuO4 crystals

Cited by in corpus (3)

• First principles-based calculation of the electrocaloric effect in BaTiO${}_3$: comparison between direct and indirect methods
• Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy Ni${}_{50}$Mn${}_{35}$In${}_{15}$
• Direct measurement of electrocaloric effect based on multi-harmonic lock-in thermography