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Entropy 2014, 16(7), 3813-3831; doi:10.3390/e16073813
Review

Phase Competitions behind the Giant Magnetic Entropy Variation: Gd5Si2Ge2 and Tb5Si2Ge2 Case Studies

1,2,†
, 1,†
, 1,2
, 1
, 3
, 3,4
, 5
, 3
, 1,*  and 1,*
1 IFIMUP and IN—Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia da Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 687, Porto 4769-007, Portugal 2 CFNUL—Centro de Física Nuclear da Universidade de Lisboa, Av. Prof. Gama Pinto, 2, Lisboa 1649-003, Portugal 3 Instituto de Nanociencia de Aragón, Universidad de Zaragoza, ES-50018 Zaragoza, Spain and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, Zaragoza 50009, Spain 4 Fundación ARAID, Zaragoza 50018, Spain 5 Instituto de Ciencia de Materiales de Aragón, CSIC-Universidad de Zaragoza, and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, Zaragoza 50009, Spain These authors contributed equally to this work.
* Authors to whom correspondence should be addressed.
Received: 11 April 2014 / Revised: 27 June 2014 / Accepted: 1 July 2014 / Published: 11 July 2014
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)
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Abstract

Magnetic materials with strong spin-lattice coupling are a powerful set of candidates for multifunctional applications because of their multiferroic, magnetocaloric (MCE), magnetostrictive and magnetoresistive effects. In these materials there is a strong competition between two states (where a state comprises an atomic and an associated magnetic structure) that leads to the occurrence of phase transitions under subtle variations of external parameters, such as temperature, magnetic field and hydrostatic pressure. In this review a general method combining detailed magnetic measurements/analysis and first principles calculations with the purpose of estimating the phase transition temperature is presented with the help of two examples (Gd5Si2Ge2 and Tb5Si2Ge2). It is demonstrated that such method is an important tool for a deeper understanding of the (de)coupled nature of each phase transition in the materials belonging to the R5(Si,Ge)4 family and most possibly can be applied to other systems. The exotic Griffiths-like phase in the framework of the R5(SixGe1-x)4 compounds is reviewed and its generalization as a requisite for strong phase competitions systems that present large magneto-responsive properties is proposed.
Keywords: entropy; phase transitions; magnetocaloric effect entropy; phase transitions; magnetocaloric effect
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Pires, A.L.; Belo, J.H.; Lopes, A.M.L.; Gomes, I.T.; Morellón, L.; Magen, C.; Algarabel, P.A.; Ibarra, M.R.; Pereira, A.M.; Araújo, J.P. Phase Competitions behind the Giant Magnetic Entropy Variation: Gd5Si2Ge2 and Tb5Si2Ge2 Case Studies. Entropy 2014, 16, 3813-3831.

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