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Phase stability of Ni-2(Mn1-xFex)Ga: A first-principles study
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2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 2, 024427- p.Article in journal (Refereed) Published
Abstract [en]

Ni-2(Mn1-xFex)Ga ferromagnetic shape memory alloy shows unusual composition-dependent martensitic transformation temperature (T-M), namely, T-M decreases with increasing e/a ratio. In hope of understanding this unusual behavior, we investigated the composition dependence of the heat of formation (H-f) and shear elastic modulus (C') of the cubic austenite as well as the stability of the five-layer modulated (5M) tetragonal martensite relative to the austenite, using first-principles exact muffin-tin orbital method in combination with coherent potential approximation. Our calculations demonstrated that H-f of the austenite increases with the Fe content x. C' increases slightly with x up to 0.05 but decreases thereafter. The composition dependence of both H-f and C' cannot fully account for the trend of T-M against x although such correlations have been proposed in literature for other Ni-Mn-Ga based alloys. The structure of 5M martensite phase of Ni-2(Mn1-xFex)Ga with 0 < x < 0.2 is determined by optimizing both the shear (changing c/a) and wavelike shuffle of atoms in (110) planes along [1 (1) over bar0] direction adopting the experimentally determined modulation function. The energy difference Delta E-AM between the austenite and 5M phases decreases with increasing x up to 0.05, following the lower Delta E-AM corresponding to lower T-M rule. However, with x larger than 0.05, Delta E-AM increases, against the experimental T-M similar to x behavior. We propose that, if taking the temperature effect and the spin-orbital coupling into account, the Delta E-AM similar to x curve might be altered and may explain the unusual composition dependence of Ni-2(Mn1-xFex)Ga.

Place, publisher, year, edition, pages
2012. Vol. 86, no 2, 024427- p.
Keyword [en]
Ni-Mn-Ga, Shape-Memory Alloys, Field-Induced Strain, Magnetic-Properties, Martensitic-Transformation, Crystal-Structures, Heusler Alloys, Potential Model, Ni2mnga, Approximation
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-101126DOI: 10.1103/PhysRevB.86.024427ISI: 000306648200005Scopus ID: 2-s2.0-84864422521OAI: oai:DiVA.org:kth-101126DiVA: diva2:546742
Funder
Swedish Research CouncilEU, European Research Council, 228074
Note

QC 20120824

Available from: 2012-08-24 Created: 2012-08-23 Last updated: 2017-12-07Bibliographically approved

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Vitos, Levente

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