Structural phase transition in GaMo4Se8and AlMo4S8by X-ray powder diffraction

François, Michel; Alexandrov, O.V.; Yvon, K.; Yaich-Aerrache, H. Ben; Gougeon, P.; Potel, M.; Sergent, M.

doi:10.1524/zkri.1992.200.1-2.47

Cited by 12 publications

(7 citation statements)

References 3 publications

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“…Consequently, the orbital degeneracy is lifted by a symmetry lowering cooperative Jahn-Teller distortion in the temperature range between 30 and 50 K, depending on the compounds. This results in rhombohedral R3m (GaV 4 S 8 , GaMo 4 S 8 , GaV 4 Se 8 , GaMo 4 Se 8 , AlMo 4 S 8 ) [4,[9][10][11][12], tetragonal P 42 1 m (GaNb 4 S 8 , GaTa 4 Se 8 ) [13,14], or orthorhombic Imm2 (GeV 4 S 8 ) [9,15] low temperature symmetries.…”

Section: Introductionmentioning

confidence: 99%

Lattice dynamics and electronic excitations in a large family of lacunar spinels with a breathing pyrochlore lattice structure

et al. 2020

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Reproducing the electronic structure of AM4X8 lacunar spinels with a breathing pyrochlore lattice is a great theoretical challenge due to the interplay of various factors. The character of the M4X4 cluster orbitals is critically influenced by the Jahn-Teller instability, the spin-orbit interaction, and also by the magnetic state of the clusters. Consequently, to reproduce the narrow-gap semiconducting nature of these moderately correlated materials requires advanced approaches, since the strength of the inter-cluster hopping is strongly affected by the character of the cluster orbitals. In order to provide a solid experimental basis for theoretical studies, we performed broadband optical spectroscopy on a large set of lacunar spinels, with systematically changing ions at the A and M sites as well as the ligand (A=Ga, Ge, Al; M=V, Mo, Nb, Ta; X=S, Se). Our study covers the range of phonon excitations and also electronic transitions near the gap edge. In the phonon excitation spectrum a limited subset of the symmetry allowed modes is observed in the cubic state, with a few additional modes emerging upon the symmetry-lowering structural transition. All the infrared active modes are assigned to vibrations of the ligands and ions at the A sites, with no obvious contribution from the M-site ions. Concerning the electronic states, we found that all compounds are narrow-gap semiconductors (Eg = 130 − 350 meV) already in their room-temperature cubic state and their structural transitions induce weak, if any, changes in the band gap. The gap value is decreased when substituting S with Se and also when replacing 3d ions by 4d or 5d ions at the M sites. :1912.11079v2 [cond-mat.str-el] arXiv

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Section: Introductionmentioning

confidence: 99%

Lattice dynamics and electronic excitations in a large family of lacunar spinels with a breathing pyrochlore lattice structure

et al. 2020

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“…AlV 4 S 8 40 [26] 10 [26] R3m [26] GaV 4 S 8 44 [33] 13 [33] R3m [20] GaV 4 Se 8 41 [31] 18 [31] R3m [26] AlMo 4 S 8 45 [92] 12 [92] R3m [92] GaNb 4 S 8 31 [24] P2 1 2 1 2 1 [13] GaNb 4 Se 8 50* [36] 33 [36] P2 1 2 1 2 1 [37] GaMo 4 S 8 45 [20] 20 [20] R3m [20] GaMo 4 Se 8 54 [93] 25 [93] R3m [92] GaTa 4 Se 8 53 [36] P2 1 2 1 2 1 [37] GeV 4 S 8 30 [76] 15 [76] Imm2 [39] We want to point out that the first lacunar spinel which was shown to become ferroelectric upon the structural transition was GeV 4 S 8 [8] . However, in contrast to all aforementioned lacunar spinels, the highest molecular orbital level of the M 4 cluster in this compound is occupied by two unpaired electrons with total spin S ¼ 1.…”

Section: Introductionmentioning

confidence: 99%

Optical, Dielectric, and Magnetoelectric Properties of Ferroelectric and Antiferroelectric Lacunar Spinels

Geirhos

Reschke

Ghara

et al. 2021

Physica Status Solidi (b)

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Lacunar spinels with a chemical formula of AM4X8 form a populous family of narrow‐gap semiconductors, which offer a fertile ground to explore correlation and quantum phenomena, including transition between Mott and spin‐orbit insulator states, ferro/antiferroelectricity driven by cluster Jahn‐Teller effect, and magnetoelectric response of magnetic skyrmions with polar dressing. The electronic and magnetic properties of lacunar spinels are determined to a large extent by their molecular‐crystal‐like structure. The interplay of electronic correlations with spin‐orbit and vibronic couplings leads to a complex electronic structure already on the single‐cluster level, which—together with weaker intercluster interactions—gives rise to a plethora of unconventional correlated states. This review primarily focuses on recent progresses in the field of optical, dielectric, and magnetoelectric properties on lacunar spinels. After introducing the main structural aspects, lattice dynamics and electronic structure of these compounds are discussed on the basis of optical spectroscopy measurements. Dielectric and polarization studies reveal the main characteristics of their low‐temperature ferro‐ or antiferroelectric phases as well as orbital fluctuations in their high‐temperature cubic state. Strong couplings between spin, lattice, and orbital degrees of freedom are manifested in singlet formation upon magnetostructural transitions, the emergence of various multiferroic phases, and exotic domain‐wall functionalities.

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“…A class of model uniaxial skyrmion hosts that exemplifies the rich topology of skyrmionic phase diagrams is the lacunar spinel family of structures. These compounds are defined by tetrahedral clusters of transition metals with a collective spin state that undergo a distortion from F43m to R3m or Imm2 symmetry upon cooling [21][22][23]. This structural symmetry breaking leads to the emergence of magnetic Dzyaloshinskii-Moriya interactions.…”

Section: Introductionmentioning

confidence: 99%

Magnetoentropic mapping and computational modeling of cycloids and skyrmions in the lacunar spinels GaV4S8 and GaV4Se8
Zuo
¹
,
Kitchaev
²
,
Schueller
³

et al. 2021
Phys. Rev. Materials
8
0
1
0
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We report the feasibility of using magnetoentropic mapping for the rapid identification of magnetic cycloid and skyrmion phases in uniaxial systems, based on the GaV4S8 and GaV4Se8 model skyrmion hosts with easyaxis and easy-plane anisotropies respectively. We show that these measurements can be interpreted with the help of a simple numerical model for the spin Hamiltonian to yield unambiguous assignments for both single phase regions and phase boundaries. In the two lacunar spinel chemistries, we obtain excellent agreement between the measured magnetoentropic features and a minimal spin Hamiltonian built on Heisenberg exchange, singleion anisotropy, and anisotropic Dzyaloshinskii-Moriya interactions. In particular, we identify characteristic high-entropy behavior in the cycloid phase that serves as a precursor to the formation of skyrmions at elevated temperatures and is a readily-measurable signature of this phase transition. Our results demonstrate that rapid magnetoentropic mapping guided by numerical modeling is an effective means of understanding the complex magnetic phase diagrams innate to skyrmion hosts. One notable exception is the observation of an anomalous, low-temperature high-entropy state in the easy-plane system GaV4Se8, which is not captured in the numerical model. Possible origins of this state are discussed.

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Structural phase transition in GaMo₄Se₈and AlMo₄S₈by X-ray powder diffraction

Cited by 12 publications

References 3 publications

Lattice dynamics and electronic excitations in a large family of lacunar spinels with a breathing pyrochlore lattice structure

Lattice dynamics and electronic excitations in a large family of lacunar spinels with a breathing pyrochlore lattice structure

Optical, Dielectric, and Magnetoelectric Properties of Ferroelectric and Antiferroelectric Lacunar Spinels

Magnetoentropic mapping and computational modeling of cycloids and skyrmions in the lacunar spinels GaV4S8 and GaV4Se8
Zuo
¹
,
Kitchaev
²
,
Schueller
³

et al. 2021
Phys. Rev. Materials
8
0
1
0
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Structural phase transition in GaMo4Se8and AlMo4S8by X-ray powder diffraction

Cited by 12 publications

References 3 publications

Lattice dynamics and electronic excitations in a large family of lacunar spinels with a breathing pyrochlore lattice structure

Lattice dynamics and electronic excitations in a large family of lacunar spinels with a breathing pyrochlore lattice structure

Optical, Dielectric, and Magnetoelectric Properties of Ferroelectric and Antiferroelectric Lacunar Spinels

Magnetoentropic mapping and computational modeling of cycloids and skyrmions in the lacunar spinels GaV4S8 and GaV4Se8Zuo1, Kitchaev2, Schueller3 et al. 2021Phys. Rev. Materials8010View full textAdd to dashboardCite

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Structural phase transition in GaMo₄Se₈and AlMo₄S₈by X-ray powder diffraction

Magnetoentropic mapping and computational modeling of cycloids and skyrmions in the lacunar spinels GaV4S8 and GaV4Se8
Zuo
¹
,
Kitchaev
²
,
Schueller
³

et al. 2021
Phys. Rev. Materials
8
0
1
0
View full text Add to dashboard Cite