Electronic structure and lattice dynamics of the magnetic shape-memory alloyCo2NiGa

Abstract

In addition to the prototypical Ni-Mn-based Heusler alloys, the Co-Ni-Ga systems have recently been suggested as another prospective materials class for magnetic shape-memory applications. We provide a characterization of the dynamical properties of this material and their relation to the electronic structure within a combined experimental and theoretical approach. This relies on inelastic neutron scattering to obtain the phonon dispersion while first-principles calculations provide the link between dynamical properties and electronic structure. In contrast to Ni 2 MnGa, where the softening of the TA 2 phonon branch is related to Fermi-surface nesting, our results reveal that the respective anomalies are absent in Co-Ni-Ga, in the phonon dispersions as well as in the electronic structure. Keywords Materials Science and Engineering Disciplines Condensed Matter Physics | Materials Science and Engineering CommentsThis article is from Physical Review B 82 (2010) In addition to the prototypical Ni-Mn-based Heusler alloys, the Co-Ni-Ga systems have recently been suggested as another prospective materials class for magnetic shape-memory applications. We provide a characterization of the dynamical properties of this material and their relation to the electronic structure within a combined experimental and theoretical approach. This relies on inelastic neutron scattering to obtain the phonon dispersion while first-principles calculations provide the link between dynamical properties and electronic structure. In contrast to Ni 2 MnGa, where the softening of the TA 2 phonon branch is related to Fermisurface nesting, our results reveal that the respective anomalies are absent in Co-Ni-Ga, in the phonon dispersions as well as in the electronic structure.

Effect of configurational order on the magnetic characteristics of Co-Ni-Ga ferromagnetic shape memory alloys

“…Overall, the lattice parameters and magnetic moments per Co atom obtained in these calculations are in good agreement with the previous calculations and experimental work. In agreement with previous theoretical studies 22,24 , the SPRKKR results suggest that the total magnetic moment increases upon tetragonal distortion. This observation is in agreement with general trends observed in experimental studies of Co-Ni-Ga alloys 42 .…”

“…From electronic structure calculations, instability in Ni 2 MnGa is due to the lack of hybridization between 3d spin-down Mn and Ni states while in Co 2 NiGa, the instability is due to the location of the Fermi level at the beginning of low-lying spin-down antibonding states 22 . Similar theoretical work by Siewert et al 24 on Co-Ni-Ga Heusler alloys seems to corroborate the results presented in 22 , although in the former case the effect of disorder on the stability of the austenite phase was examined by exploring conventional Heusler L2 1 ordering as well as so-called inverse Heusler configurations in which one of the majority atoms-Co in this case-is replaced by either of the minority components-Ni or Ga in this instance.…”

“…We would like to note that the SPRKKR code is unable to correctly predict the fact that the tetragonal structure (i. e. martensite) is more stable than the cubic structure under shear deformations and we have used results obtained earlier 22,24 and assumed that the martensite has a c/a ratio of approximately ∼ 1.4. The reason for this is unclear but a possible explanation may lie on rather subtle effects related to the effect of symmetry breaking (under the tetragonal distortion) on d-electrons of Co and Ni.…”

First-principles study of the lattice instabilities in Mn2NiX(X= Al, Ga, In, Sn) magnetic shape memory alloys

“…However, this cannot be generalized for all ternary alloys showing martensitic instabilities. For Co 2 NiGa, a newly found shape memory alloy, Siewart et al 35 observed that softening in TA 2 phonon branch was absent as a result of nonappearance of nesting features in the Fermi surfaces of Co 2 NiGa. Here, we present Fermi surfaces corresponding to the spin-minority bands only, since most prominent features are observed in this spin channel as the systems undergo martensitic transitions 19 .…”

Stability analysis of the martensitic phase transformation inCo2NiGaHeusler alloy

“…To be able to realize the advantages offered by these multi-functional materials in the automotive , aerospace and heavy machinery industries, there is a requirement for SMAs with much higher transformation temperatures. CoNiGa is one such promising shape memory alloy (SMA) which is the object of much interest due to it's potential as a magnetic SMA with a thermoelastic transition in the ferromagnetic state 1 . Cobalt has a large magnetic moment which ensures a high Curie temperature.…”