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Contributions to the Transformation Entropy Change and Influencing Factors in Metamagnetic Ni-Co-Mn-Ga Shape Memory Alloys

Departament de Física, Universitat de les Illes Balears, Campus universitari, Ctra. de Valldemossa km 7.5, 07122 Palma de Mallorca, Spain
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Entropy 2014, 16(10), 5560-5574; https://doi.org/10.3390/e16105560
Received: 17 September 2014 / Revised: 15 October 2014 / Accepted: 16 October 2014 / Published: 22 October 2014
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)
Ni-Co-Mn-Ga ferromagnetic shape memory alloys show metamagnetic transition from ferromagnetic austenite to paramagnetic (or weak-magnetic) martensite for a limited range of Co contents. The temperatures of the structural and magnetic transitions depend strongly on composition and atomic order degree, in such a way that combined composition and thermal treatment allows obtaining martensitic transformation (MT) between any magnetic state of austenite and martensite. The entropy change ΔS measured in the magnetostructural transition comprises a magnetic contribution which depends on the type and degree of magnetic order of the related phases. Consequently, both the magnetization jump across the MT (ΔM) and ΔS are composition and atomic order dependent. Both ΔS and ΔM determine the effect of applied magnetic fields on the MT, hence knowledge and understanding of their behavior can help to approach the best conditions for magnetic field induced MT and related effects. In previous papers, we have reported findings regarding the behavior of the transformation entropy in relation to composition and atomic order in Ni50xCoxMn25+yGa25y (x = 3–8, y = 5–7) alloys. In the present paper we will review our recent results, summarizing the key findings and drawing general conclusions regarding the magnetic contribution to ΔS and the effect of different factors on the magnetic and structural properties of these metamagnetic alloys. View Full-Text
Keywords: Ni-Co-Mn-Ga; transformation entropy change; atomic order; metamagnetic shape memory alloys Ni-Co-Mn-Ga; transformation entropy change; atomic order; metamagnetic shape memory alloys
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Seguí, C.; Cesari, E. Contributions to the Transformation Entropy Change and Influencing Factors in Metamagnetic Ni-Co-Mn-Ga Shape Memory Alloys. Entropy 2014, 16, 5560-5574.

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