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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Y(FeGe)2 by Materials Project

YFe2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Y is bonded in a 8-coordinate geometry to eight equivalent Fe and eight equivalent Ge atoms. All Y–Fe bond lengths are 3.23 Å. All Y–Ge bond lengths are 3.10 Å. Fe is bonded to four equivalent Y and four equivalent Ge atoms to form a mixture of distorted edge, face, and corner-sharing FeY4Ge4 tetrahedra. All Fe–Ge bond lengths are 2.35 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Y, four equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.61 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pr(FeGe)2 by Materials Project

PrFe2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Pr is bonded in a 8-coordinate geometry to eight equivalent Fe and eight equivalent Ge atoms. All Pr–Fe bond lengths are 3.38 Å. All Pr–Ge bond lengths are 3.16 Å. Fe is bonded to four equivalent Pr and four equivalent Ge atoms to form a mixture of distorted corner, edge, and face-sharing FePr4Ge4 tetrahedra. All Fe–Ge bond lengths are 2.45 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Pr, four equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.65 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Dy(FeGe)2 by Materials Project

DyFe2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Dy is bonded in a 8-coordinate geometry to eight equivalent Fe and eight equivalent Ge atoms. All Dy–Fe bond lengths are 3.23 Å. All Dy–Ge bond lengths are 3.10 Å. Fe is bonded to four equivalent Dy and four equivalent Ge atoms to form a mixture of distorted corner, edge, and face-sharing FeDy4Ge4 tetrahedra. All Fe–Ge bond lengths are 2.35 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Dy, four equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.60 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb(FeGe)6 by Materials Project

TbFe6Ge6 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Tb is bonded to twelve Fe and eight Ge atoms to form distorted TbFe12Ge8 hexagonal bipyramids that share corners with four equivalent TbFe12Ge8 hexagonal bipyramids, faces with eight equivalent FeTb2Fe4Ge6 cuboctahedra, and faces with four equivalent TbFe12Ge8 hexagonal bipyramids. There are a spread of Tb–Fe bond distances ranging from 3.25–3.30 Å. There are a spread of Tb–Ge bond distances ranging from 2.84–3.00 Å. There are three inequivalent Fe sites. In the first Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent Tb, four Fe, and six Ge atoms. All Fe–Fe bond lengths are 2.56 Å. There are a spread of Fe–Ge bond distances ranging from 2.48–2.68 Å. In the second Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent Tb, four Fe, and six Ge atoms. Both Fe–Fe bond lengths are 2.57 Å. There are four shorter (2.52 Å) and two longer (2.67 Å) Fe–Ge bond lengths. In the third Fe site, Fe is bonded to two equivalent Tb, four Fe, and six Ge atoms to form distorted FeTb2Fe4Ge6 cuboctahedra that share corners with four equivalent FeTb2Fe4Ge6 cuboctahedra, edges with two equivalent FeTb2Fe4Ge6 cuboctahedra, faces with four equivalent FeTb2Fe4Ge6 cuboctahedra, and faces with four equivalent TbFe12Ge8 hexagonal bipyramids. Both Fe–Fe bond lengths are 2.57 Å. There are a spread of Fe–Ge bond distances ranging from 2.51–2.69 Å. There are five inequivalent Ge sites. In the first Ge site, Ge is bonded in a 8-coordinate geometry to two equivalent Tb and six Fe atoms. In the second Ge site, Ge is bonded in a 6-coordinate geometry to six Fe atoms. In the third Ge site, Ge is bonded in a 9-coordinate geometry to three equivalent Tb and six Fe atoms. In the fourth Ge site, Ge is bonded in a 8-coordinate geometry to one Tb, six Fe, and one Ge atom. The Ge–Ge bond length is 2.50 Å. In the fifth Ge site, Ge is bonded in a 7-coordinate geometry to one Tb and six Fe atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(FeGe)2 by Materials Project

CeFe2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight equivalent Fe and eight equivalent Ge atoms. All Ce–Fe bond lengths are 3.21 Å. All Ce–Ge bond lengths are 3.19 Å. Fe is bonded in a 4-coordinate geometry to four equivalent Ce and four equivalent Ge atoms. All Fe–Ge bond lengths are 2.34 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Ce, four equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.67 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti(FeGe)6 by Materials Project

TiFe6Ge6 crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. Ti is bonded to eight Ge atoms to form distorted edge-sharing TiGe8 hexagonal bipyramids. There are two shorter (2.67 Å) and six longer (2.87 Å) Ti–Ge bond lengths. Fe is bonded in a 12-coordinate geometry to six Ge atoms. There are a spread of Fe–Ge bond distances ranging from 2.45–2.58 Å. There are three inequivalent Ge sites. In the first Ge site, Ge is bonded in a 6-coordinate geometry to six equivalent Fe atoms. In the second Ge site, Ge is bonded in a 12-coordinate geometry to three equivalent Ti and six equivalent Fe atoms. In the third Ge site, Ge is bonded in a 8-coordinate geometry to one Ti, six equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.62 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sm(FeGe)2 by Materials Project

SmFe2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sm is bonded in a 8-coordinate geometry to eight equivalent Fe and eight equivalent Ge atoms. All Sm–Fe bond lengths are 3.35 Å. All Sm–Ge bond lengths are 3.11 Å. Fe is bonded to four equivalent Sm and four equivalent Ge atoms to form a mixture of distorted face, edge, and corner-sharing FeSm4Ge4 tetrahedra. All Fe–Ge bond lengths are 2.44 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Sm, four equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.58 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(FeGe)2 by Materials Project

HoFe2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho is bonded in a 8-coordinate geometry to eight equivalent Fe and eight equivalent Ge atoms. All Ho–Fe bond lengths are 3.32 Å. All Ho–Ge bond lengths are 3.05 Å. Fe is bonded to four equivalent Ho and four equivalent Ge atoms to form a mixture of edge, corner, and face-sharing FeHo4Ge4 tetrahedra. All Fe–Ge bond lengths are 2.43 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Ho, four equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.51 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Er(FeGe)2 by Materials Project

ErFe2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Er is bonded in a 8-coordinate geometry to eight equivalent Fe and eight equivalent Ge atoms. All Er–Fe bond lengths are 3.23 Å. All Er–Ge bond lengths are 3.08 Å. Fe is bonded to four equivalent Er and four equivalent Ge atoms to form a mixture of distorted edge, face, and corner-sharing FeEr4Ge4 tetrahedra. All Fe–Ge bond lengths are 2.35 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Er, four equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.57 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Gd(FeGe)2 by Materials Project

GdFe2Ge2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Gd is bonded in a 8-coordinate geometry to eight equivalent Fe and eight equivalent Ge atoms. There are a spread of Gd–Fe bond distances ranging from 3.30–3.37 Å. There are four shorter (3.08 Å) and four longer (3.09 Å) Gd–Ge bond lengths. Fe is bonded to four equivalent Gd and four equivalent Ge atoms to form a mixture of distorted edge, corner, and face-sharing FeGd4Ge4 tetrahedra. There are one shorter (2.43 Å) and three longer (2.44 Å) Fe–Ge bond lengths. Ge is bonded in a 9-coordinate geometry to four equivalent Gd, four equivalent Fe, and one Ge atom. The Ge–Ge bond length is 2.54 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Centrosymmetric or Noncentrosymmetric? Transition Metals Talking in K 2 TGe 3 S 8 (T = Co, Fe)

Two new quaternary sulfides K 2 TGe 3 S 8 (T=Co, Fe) have been synthesized by a high-temperature solid-state routine and flux growth method. The crystal growth process of K 2 TGe 3 S 8 (T=Co, Fe) was elucidated by in-situ powder X-ray diffraction and DSC thermal analysis. The mm-sized crystals of K 2 TGe 3 S 8 (T=Co, Fe) were grown. K 2 CoGe 3 S 8 crystallizes in a new structure type in centrosymmetric space group P1¯ (No. 2) with unit cell parameters of a = 7.016(1) Å, b = 7.770(1)Å, c = 14.342(1) Å, α = 93.80(1)°, β = 92.65(1)°, γ = 114.04(1)°. K 2 FeGe 3 S 8 crystallizes in K 2 FeGe 3 Se 8 structure type and the noncentrosymmetric space group P2 1 (No. 4) with unit cell parameters of a = 7.1089(5)Å, b = 11.8823(8)Å, c = 16.7588(11)Å, β = 96.604(2)°. There is a high structural similarity between K 2 CoGe 3 S 8 and K 2 FeGe 3 S 8 . The larger volume coupled with higher degrees of distortion of [FeS 4 ] tetrahedra compared to [CoS 4 ] tetrahedra accounts for the structure’s shift from centrosymmetric to noncentrosymmetric. The theory simulation confirms that [TS 4 ]T= Co or Fe tetrahedra play a crucial role in controlling the structure and properties of K 2 TGe 3 S 8 (T = Co, Fe). The measured optical bandgaps of K 2 CoGe 3 S 8 and K 2 FeGe 3 S 8 are 2.1(1) eV and 2.6(1) eV respectively. K 2 FeGe 3 S 8 shows antiferromagnetic ordering at 24K while no magnetic ordering was detected in K 2 CoGe 3 S 8 . In conclusion, the magnetic measurements also demonstrate the divalent nature of transition metals in K 2 TGe 3 S 8 (T = Co, Fe).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Discovery of charge density wave in a kagome lattice antiferromagnet

A hallmark of strongly correlated quantum materials is the rich phase diagram resulting from competing and intertwined phases with nearly degenerate ground state energies. A well-known example is the copper oxides, where a charge density wave (CDW) is ordered well above and strongly coupled to the magnetic order to form spin-charge separated stripes that compete with superconductivity. Recently, such rich phase diagrams have also been revealed in correlated topological materials. In two-dimensional kagome lattice metals consisting of corner-sharing triangles, the geometry of the lattice can produce flat bands with localized electrons, non-trivial topology, chiral magnetic order, superconductivity and CDW order. While CDW has been found in weakly electron correlated nonmagnetic AV 3 Sb 5 (A = K, Rb, Cs), it has not yet been observed in correlated magnetic ordered kagome lattice metals. Here we report the discovery of CDW within the antiferromagnetic (AFM) ordered phase of kagome lattice FeGe. The CDW in FeGe occurs at wavevectors identical to that of AV 3 Sb 5 , enhances the AFM ordered moment, and induces an emergent anomalous Hall effect. Furthermore, our findings suggest that CDW in FeGe arises from the combination of electron correlations-driven AFM order and van Hove singularities-driven instability possibly associated with a chiral flux phase, in stark contrast to strongly correlated copper oxides and nickelates, where the CDW precedes or accompanies the magnetic order.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Spin-Charge-Lattice Coupling across the Charge Density Wave Transition in a Kagome Lattice Antiferromagnet

Understanding spin and lattice excitations in a metallic magnetic ordered system forms the basis to unveil the magnetic and lattice exchange couplings and their interactions with itinerant electrons. Kagome lattice antiferromagnet FeGe is interesting because it displays a rare charge density wave (CDW) deep inside the antiferromagnetic ordered phase that interacts with the magnetic order. Here, we use neutron scattering to study the evolution of spin and lattice excitations across the CDW transition 𝑇 CDW in FeGe. While spin excitations below ∼100 meV can be well described by spin waves of a spin-1 Heisenberg Hamiltonian, spin excitations at higher energies are centered around the Brillouin zone boundary and extend up to ∼180 meV consistent with quasiparticle excitations across spin-polarized electron-hole Fermi surfaces. Furthermore, 𝑐-axis spin wave dispersion and Fe-Ge optical phonon modes show a clear hardening below 𝑇 CDW due to spin-charge-lattice coupling but with no evidence of a phonon Kohn anomaly. By comparing our experimental results with density functional theory calculations in absolute units, we conclude that FeGe is a Hund’s metal in the intermediate correlated regime where magnetism has contributions from both itinerant and localized electrons arising from spin polarized electronic bands near the Fermi level.

charge density waves↗
DOE OSTI2025

Disentangling the intertwined orders in a magnetic kagome metal

Intertwined orders appear when multiple orders are strongly interacting, and kagome metals have emerged as new platforms to explore exotic phases. FeGe has been found to develop a charge density wave (CDW) order within magnetic phase, suggesting an intricate interplay of the lattice, charge, and spin degrees of freedom. Recently, postgrowth annealing has been proposed to tune the CDW order from long-range to complete suppression, offering a tuning knob for the CDW order. Here, by comparing the electronic structures of FeGe subjected to different annealing conditions and distinct CDW properties, we report spectral evolution associated with the lattice and spin degrees of freedom. We find band evolution linked to a spin density wave (SDW) order present in both samples with and without CDW order, and another evolution connected to the lattice distortions that onset with the long-range CDW order and revert with the SDW order. Our results reveal a rare competitive cooperation of the lattice, spin, and charge in FeGe.

Oh, Ji Seop↗
DOE OSTI2021

Synthesis, structural, and magnetic properties of Heusler-type Mn 2-x Fe 1+x Ge (0.0 ≤ x ≤ 1.0) alloys

Bulk Mn 2-x Fe 1+x Ge (0.0 ≤ x ≤ 1.0) alloys have been synthesized by arc-melting followed by a low temperature homogenization thermal annealing, whereas for comparison purposes the Mn 2 FeGe alloy was also produced in ribbon form by rapid solidification. Here, a study of the structural and magnetic properties is presented. Contrary to theoretical predictions, Mn 2 FeGe crystallizes in a hexagonal DO 19 crystal structure (space group P63/mmc) and orders ferromagnetically with a saturation magnetization (M S ) value of ~1.7 µB/f.u. in the ground state. With the substitution of Fe for Mn in bulk Mn 2-x Fe 1+x Ge, we observed an increase in the FM interactions with a maximum MS value of 5.1 µ B /f.u. for x = 1.0, and a significant progressive increase in the Curie temperature (T C ) in a wide range spanning ~200 K to over 400 K.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Signature of spin-phonon coupling driven charge density wave in a kagome magnet

Abstract The intertwining between spin, charge, and lattice degrees of freedom can give rise to unusual macroscopic quantum states, including high-temperature superconductivity and quantum anomalous Hall effects. Recently, a charge density wave (CDW) has been observed in the kagome antiferromagnet FeGe, indicative of possible intertwining physics. An outstanding question is that whether magnetic correlation is fundamental for the spontaneous spatial symmetry breaking orders. Here, utilizing elastic and high-resolution inelastic x-ray scattering, we observe a c-axis superlattice vector that coexists with the 2 $$\times$$ × 2 $$\times$$ × 1 CDW vectors in the kagome plane. Most interestingly, between the magnetic and CDW transition temperatures, the phonon dynamical structure factor shows a giant phonon-energy hardening and a substantial phonon linewidth broadening near the c-axis wavevectors, both signaling the spin-phonon coupling. By first principles and model calculations, we show that both the static spin polarization and dynamic spin excitations intertwine with the phonon to drive the spatial symmetry breaking in FeGe.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗