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Inapplicability of the Maxwell relation for the quantification of caloric effects in anisotropic ferroic materials / R. Niemann in International journal of refrigeration, Vol. 37 N° 1 (Janvier 2014) 

Public ISBD [article]  in International journal of refrigeration > Vol. 37 N° 1 (Janvier 2014) . - pp. 281–288 Titre : Inapplicability of the Maxwell relation for the quantification of caloric effects in anisotropic ferroic materials Titre original : Inapplicabilité de la relation de Maxwell pour la quantification des effets calorifiques dans des matériaux ferroïques anisotropiques Type de document : texte imprimé Auteurs : R. Niemann, Auteur ; O. Heczko, Auteur ; L. Schultz, Auteur Année de publication : 2014 Article en page(s) : pp. 281–288 Note générale : Refrigeration Langues : Anglais (eng) Mots-clés : Magnetocaloric;  shape  memory  alloys;  multiferroic;  Ni-Mn-Ga;  Maxwell  relation Résumé : 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. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700713002314 [article] Inapplicability of the Maxwell relation for the quantification of caloric effects in anisotropic ferroic materials = Inapplicabilité de la relation de Maxwell pour la quantification des effets calorifiques dans des matériaux ferroïques anisotropiques [texte imprimé] / R. Niemann, Auteur ; O. Heczko, Auteur ; L. Schultz, Auteur . - 2014 . - pp. 281–288. Refrigeration Langues : Anglais (eng) in International journal of refrigeration > Vol. 37 N° 1 (Janvier 2014) . - pp. 281–288 Mots-clés : Magnetocaloric;  shape  memory  alloys;  multiferroic;  Ni-Mn-Ga;  Maxwell  relation Résumé : 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. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700713002314