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Special Issue "Entropy in Shape Memory Alloys"

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A special issue of Entropy (ISSN 1099-4300).

Deadline for manuscript submissions: closed (25 September 2014)

Special Issue Editor

Guest Editor
Prof. Dr. Lluís Mañosa

Group of Condensed Matter Physics, Department of Structure and Constituents of Matter, University of Barcelona, Diagonal 647, Barcelona, 08028, Catalonia, Spain
E-Mail
Interests: phase transitions in solids; thermal; magnetic and electric porperties of solids; multifunctional materials; giant caloric effects and magnetic shape memory

Special Issue Information

Dear Colleagues,

Shape memory alloys are capable of recovering from very large deformations when heated above a certain temperature. Such a peculiar porperty is a consequence of a structural phase transition (martensitic transition) between an open cubic phase and a lower symmetry closer packed phase. The relative phase stability between these structures is, to a large extent, controlled by their entropy difference. In recent years, a new family of shape  alloys have been discovered, magnetic shape memory alloys,  in which shape change can be achieved by magnetic field. A strong coupling between structural and magnetic degrees of freedom occurs in these alloys, and spin contributions  to the solid entropy plays a crucial role.  In addition to the unique mechanical properties, very recently it has been shown that shape memory alloys are also good candidates for environment friendly solid-state refrigeration. Giant caloric properties such as magnetocaloric, elastocaloric and barocaloric effects have been reported for many of these alloys, where the key feature for the effect to be giant is the large entropy change that can be induced by application of an external field (magnetic or mechanical), which is the result of the entropy difference of the two structural phases involved in the martensitic transition. We welcome submissions addressing any aspect related to entropy in the martensitic transition of shape memory alloys.

Specific topics of interest include (but are not limited to):

  • relative phase stability
  • electronic and phonon densities of states
  • magnetostructural coupling
  • magnetocaloric effects
  • mechanic-caloric (barocaloric and elastocaloric) effects
  • kinetic arrest

Prof. Dr. Lluís Mañosa
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Entropy is an international peer-reviewed Open Access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs).

Keywords

  • martensitic transition
  • relative phase stability
  • shape memory and magnetic shape memory
  • magnetocaloric, barocaloric and elastocaloric effects
  • vibrational, electronic and magnetic contributions to entropy

Published Papers (6 papers)

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Research

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Open AccessArticle Contributions to the Transformation Entropy Change and Influencing Factors in Metamagnetic Ni-Co-Mn-Ga Shape Memory Alloys
Entropy 2014, 16(10), 5560-5574; doi:10.3390/e16105560
Received: 17 September 2014 / Revised: 15 October 2014 / Accepted: 16 October 2014 / Published: 22 October 2014
Cited by 2 | PDF Full-text (1321 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)
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Open AccessArticle Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys
Entropy 2014, 16(9), 4992-5019; doi:10.3390/e16094992
Received: 25 August 2014 / Revised: 12 September 2014 / Accepted: 12 September 2014 / Published: 19 September 2014
Cited by 9 | PDF Full-text (725 KB) | HTML Full-text | XML Full-text
Abstract
The complex magnetic and structural properties of Co-doped Ni-Mn-Ga Heusler alloys have been investigated by using a combination of first-principles calculations and classical Monte Carlo simulations. We have restricted the investigations to systems with 0, 5 and 9 at% Co. Ab initio calculations
[...] Read more.
The complex magnetic and structural properties of Co-doped Ni-Mn-Ga Heusler alloys have been investigated by using a combination of first-principles calculations and classical Monte Carlo simulations. We have restricted the investigations to systems with 0, 5 and 9 at% Co. Ab initio calculations show the presence of the ferrimagnetic order of austenite and martensite depending on the composition, where the excess Mn atoms on Ga sites show reversed spin configurations. Stable ferrimagnetic martensite is found for systems with 0 (5) at% Co and a c=a ratio of 1.31 (1.28), respectively, leading to a strong competition of ferro- and antiferro-magnetic exchange interactions between nearest neighbor Mn atoms. The Monte Carlo simulations with ab initio exchange coupling constants as input parameters allow one to discuss the behavior at finite temperatures and to determine magnetic transition temperatures. The Curie temperature of austenite is found to increase with Co, while the Curie temperature of martensite decreases with increasing Co content. This behavior can be attributed to the stronger Co-Mn, Mn-Mn and Mn-Ni exchange coupling constants in austenite compared to the corresponding ones in martensite. The crossover from a direct to inverse magnetocaloric effect in Ni-Mn-Ga due to the substitution of Ni by Co leads to the appearance of a “paramagnetic gap” in the martensitic phase. Doping with In increases the magnetic jump at the martensitic transition temperature. The simulated magnetic and magnetocaloric properties of Co- and In-doped Ni-Mn-Ga alloys are in good qualitative agreement with the available experimental data. Full article
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)
Open AccessArticle Long-Range Atomic Order and Entropy Change at the Martensitic Transformation in a Ni-Mn-In-Co Metamagnetic Shape Memory Alloy
Entropy 2014, 16(5), 2756-2767; doi:10.3390/e16052756
Received: 4 April 2014 / Revised: 28 April 2014 / Accepted: 14 May 2014 / Published: 19 May 2014
Cited by 4 | PDF Full-text (598 KB) | HTML Full-text | XML Full-text
Abstract
The influence of the atomic order on the martensitic transformation entropy change has been studied in a Ni-Mn-In-Co metamagnetic shape memory alloy through the evolution of the transformation temperatures under high-temperature quenching and post-quench annealing thermal treatments. It is confirmed that the entropy
[...] Read more.
The influence of the atomic order on the martensitic transformation entropy change has been studied in a Ni-Mn-In-Co metamagnetic shape memory alloy through the evolution of the transformation temperatures under high-temperature quenching and post-quench annealing thermal treatments. It is confirmed that the entropy change evolves as a consequence of the variations on the degree of L21 atomic order brought by thermal treatments, though, contrary to what occurs in ternary Ni-Mn-In, post-quench aging appears to be the most effective way to modify the transformation entropy in Ni-Mn-In-Co. It is also shown that any entropy change value between around 40 and 5 J/kgK can be achieved in a controllable way for a single alloy under the appropriate aging treatment, thus bringing out the possibility of properly tune the magnetocaloric effect. Full article
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)
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Open AccessArticle Co and In Doped Ni-Mn-Ga Magnetic Shape Memory Alloys: A Thorough Structural, Magnetic and Magnetocaloric Study
Entropy 2014, 16(4), 2204-2222; doi:10.3390/e16042204
Received: 20 March 2014 / Revised: 10 April 2014 / Accepted: 10 April 2014 / Published: 16 April 2014
Cited by 17 | PDF Full-text (1932 KB) | HTML Full-text | XML Full-text
Abstract
In Ni-Mn-Ga ferromagnetic shape memory alloys, Co-doping plays a major role in determining a peculiar phase diagram where, besides a change in the critical temperatures, a change of number, order and nature of phase transitions (e.g., from ferromagnetic to paramagnetic or from paramagnetic
[...] Read more.
In Ni-Mn-Ga ferromagnetic shape memory alloys, Co-doping plays a major role in determining a peculiar phase diagram where, besides a change in the critical temperatures, a change of number, order and nature of phase transitions (e.g., from ferromagnetic to paramagnetic or from paramagnetic to ferromagnetic, on heating) can be obtained, together with a change in the giant magnetocaloric effect from direct to inverse. Here we present a thorough study of the intrinsic magnetic and structural properties, including their dependence on hydrostatic pressure, that are at the basis of the multifunctional behavior of Co and In-doped alloys. We study in depth their magnetocaloric properties, taking advantage of complementary calorimetric and magnetic techniques, and show that if a proper measurement protocol is adopted they all merge to the same values, even in case of first order transitions. A simplified model for the estimation of the adiabatic temperature change that relies only on indirect measurements is proposed, allowing for the quick and reliable evaluation of the magnetocaloric potentiality of new materials starting from readily available magnetic measurements. Full article
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)
Open AccessArticle Entropy Change during Martensitic Transformation in Ni50−xCoxMn50−yAly Metamagnetic Shape Memory Alloys
Entropy 2014, 16(3), 1808-1818; doi:10.3390/e16031808
Received: 12 February 2014 / Revised: 18 March 2014 / Accepted: 19 March 2014 / Published: 24 March 2014
Cited by 2 | PDF Full-text (1317 KB) | HTML Full-text | XML Full-text
Abstract
Specific heat was systematically measured by the heat flow method in Ni50-xCoxMn50-yAly metamagnetic shape memory alloys near the martensitic transformation temperatures. Martensitic transformation and ferromagnetic–paramagnetic transition for the parent phase were directly observed via
[...] Read more.
Specific heat was systematically measured by the heat flow method in Ni50-xCoxMn50-yAly metamagnetic shape memory alloys near the martensitic transformation temperatures. Martensitic transformation and ferromagnetic–paramagnetic transition for the parent phase were directly observed via the specific heat measurements. On the basis of the experimental results, the entropy change was estimated and it was found to show an abrupt decrease below the Curie temperature. The results were found to be consistent with those of earlier studies on Ni-Co-Mn-Al alloys. Full article
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)

Review

Jump to: Research

Open AccessReview Phase Competitions behind the Giant Magnetic Entropy Variation: Gd5Si2Ge2 and Tb5Si2Ge2 Case Studies
Entropy 2014, 16(7), 3813-3831; doi:10.3390/e16073813
Received: 11 April 2014 / Revised: 27 June 2014 / Accepted: 1 July 2014 / Published: 11 July 2014
Cited by 6 | PDF Full-text (1484 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)
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