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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Unconventional Anomalous Hall Effect in Hexagonal Polar Magnet Y 3 Co 8 Sn 4

A rare realization of unconventional anomalous Hall effect (UAHE) both below and above the magnetic transition temperature (T C ) in a hexagonal noncentrosymmetric magnet Y 3 Co 8 Sn 4 , using a combined experimental and ab initio calculations. Occurrence of such UAHE is mainly attributed to the reciprocal ($\mathscr{KS}$) topology (i.e., the presence of topological Weyl points at/near the Fermi level), along with some contribution from the topological magnetic texture (at low temperatures), as inferred from the measured field-dependent ac susceptibility. The effect of UAHE on the measured transport behavior however evolves differently with temperature above and below T C = 53 K, suggesting different physical mechanism responsible in the two phases. A unique planar ferrimagnetic ordering is found to be the most stable state with ab-plane as the easy plane below T C . The simulated net magnetization and the moment per Co atom agrees fairly well with the experimentally measured values. A reasonably large anomalous Hall conductivity (AHC) is also observed in both the phases (above and below T C ) of the present compound, which is again not so ubiquitous. In conclusion, the results underscore the family of R 3 Co 8 Sn 4 (R = rare earth) polar magnets as a compelling backdrop for exploring the synergy of magnetism and topological non-trivial electronic states, pivotal for spintronic applications.

Density functional theory calculations↗
DOE OSTI2022

Quantum Sensing and Imaging of Spin–Orbit-Torque-Driven Spin Dynamics in the Non-Collinear Antiferromagnet Mn 3 Sn

Novel non-collinear antiferromagnets with spontaneous time-reversal symmetry breaking, non-trivial band topology, and unconventional transport properties have received immense research interest over the past decade due to their rich physics and enormous promise in technological applications. One of the central focuses in this emerging field is exploring the relationship between the microscopic magnetic structure and exotic material properties. Nanoscale imaging of both spin–orbit-torque-induced deterministic magnetic switching and chiral spin rotation in non-collinear antiferromagnet Mn 3 Sn films using nitrogen-vacancy (NV) centers are reported. Direct evidence of the off-resonance dipole–dipole coupling between the spin dynamics in Mn 3 Sn and proximate NV centers is also demonstrated by NV relaxometry measurements. These results demonstrate the unique capabilities of NV centers in accessing the local information of the magnetic order and dynamics in these emergent quantum materials and suggest new opportunities for investigating the interplay between topology and magnetism in a broad range of topological magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Dimetalloylene (M‐E‐M) Complexes of Heavier Main Group Elements Ge, Sn, Pb, Bi via Cleavage of E‐X Bonds (X=N(SiMe 3 ) 2 , O t Bu) with an Iridium Hydride

Abstract Reactions of the Ir V hydride [ Me BDI Dipp ]IrH 4 {BDI=(Dipp)NC(Me)CH(Me)CN(Dipp); Dipp=2,6‐ i Pr 2 C 6 H 3 } with E[N(SiMe 3 ) 2 ] 2 (E=Sn, Pb) afforded the unusual dimeric dimetallotetrylenes ([ Me BDI Dipp ]IrH) 2 ( μ 2 ‐E) 2 in good yields. Moreover, ([ Me BDI Dipp ]IrH) 2 ( μ 2 ‐Ge) 2 was formed in situ from thermal decomposition of [ Me BDI Dipp ]Ir(H) 2 Ge[N(SiMe 3 ) 2 ] 2 . These reactions are accompanied by liberation of HN(SiMe 3 ) 2 and H 2 through the apparent cleavage of an E−N(SiMe 3 ) 2 bond by Ir−H. In a reversal of this process, ([ Me BDI Dipp ]IrH) 2 ( μ 2 ‐E) 2 reacted with excess H 2 to regenerate [ Me BDI Dipp ]IrH 4 . Varying the concentrations of reactants led to formation of the trimeric ([ Me BDI Dipp ]IrH 2 ) 3 ( μ 2 ‐E) 3 . The further scope of this synthetic route was investigated with group 15 amides, and ([ Me BDI Dipp ]IrH) 2 ( μ 2 ‐Bi) 2 was prepared by the reaction of [ Me BDI Dipp ]IrH 4 with Bi(NMe 2 ) 3 or Bi(O t Bu) 3 to afford the first example of a “naked” two‐coordinate Bi atom bound exclusively to transition metals. A viable mechanism that accounts for the formation of these products is proposed. Computational investigations of the Ir 2 E 2 (E=Sn, Pb) compounds characterized them as open‐shell singlets with confined nonbonding lone pairs at the E centers. In contrast, Ir 2 Bi 2 is characterized as having a closed‐shell singlet ground state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Modifying the Reactivity of Single Pd Sites in a Trimetallic Sn‐Pd‐Ag Surface Alloy: Tuning CO Binding Strength

Abstract Improving control over active‐site reactivity is a grand challenge in catalysis. Single‐atom alloys (SAAs) consisting of a reactive component doped as single atoms into a more inert host metal feature localized and well‐defined active sites, but fine tuning their properties is challenging. Here, a framework is developed for tuning single‐atom site reactivity by alloying in an additional inert metal, which this work terms an alloy‐host SAA. Specifically, this work creates about 5% Pd single‐atom sites in a Pd 33 Ag 67 (111) single crystal surface, and then identifies Sn based on computational screening as a suitable third metal to introduce. Subsequent experimental studies show that introducing Sn indeed modifies the electronic structure and chemical reactivity (measured by CO desorption energies) of the Pd sites. The modifications to both the electronic structure and the CO adsorption energies are in close agreement with the calculations. These results indicate that the use of an alloy host environment to modify the reactivity of single‐atom sites can allow fine‐tuning of catalytic performance and boost resistance against strong‐binding adsorbates such as CO.

Mohrhusen, Lars↗
DOE OSTI2024

Microstructural Coarsening Kinetics and Mechanical Property Changes in Long-Term Aged Sn–Pb–Sb Solder Joints

Tin-lead-antimony (50Sn–47Pb–3Sb wt.%) soldered assemblies were mechanically tested approximately 30 years after initial production and found to have solder joints of reduced strength. The microstructure of this solder alloy exhibits a ternary eutectic structure with Sn-rich, Pb-rich, and SnSb phases. Accelerated aging was performed to evaluate solder microstructural coarsening and associated strength of laboratory solder joints to correlate these properties to the “naturally aged” solder joints. Isothermal aging was conducted at room temperature, 55, 70, 100, and 135 °C and aging times that ranged from 0.1 to 365 days. The coarsening kinetics of the Pb-rich phase were determined through optical microscopy and image analysis methods established in previous studies on binary Sn–Pb solder. A kinetic equation was developed with time exponent n of 0.43 and activation energy of 24000 J/mol, suggesting grain boundary diffusion or other fast diffusion pathways controlling the microstructural evolution. Compression testing and Vickers microhardness showed significant strength loss within the first 20–30 days after soldering; then, the microstructure and mechanical properties changed more slowly over long periods of time. Further, by combining accelerated aging data and the microstructure-based kinetics, strength predictions were made that match well with the properties of the actual soldered assemblies naturally aged for 30 years. However, aging at the highest temperature of 135 °C produced anomalous behavior suggesting that extraneous aging mechanisms are active. Therefore, data obtained at this temperature or higher should not be used. Overall, the combined microstructural and mechanical property methods used in this study confirmed that the observed reduction in strength of ~ 30-year-old solder joints can be accounted for by the microstructural coarsening that takes place during long-term solid-state aging.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Corrosion in Other Liquid Metals (Li, PbLi, Hg, Sn, Ga)

A wide range of liquid metals have been considered for application in nuclear fission and fusion reactors. Liquid mercury (Hg) was tested as a coolant and working fluid for nuclear fission reactors and as a neutron source target. Liquid lithium and lead lithium eutectic (Li and PbLi) have been extensively studied for fusion reactor designs including plasma facing components (PFCs). Liquid tin and gallium (Sn and Ga) have recently gained attention as alternative PFCs due to their low vapor pressure and chemical stability. To enable successful application of these less common liquid metals, corrosion compatibility with containment materials needs to be investigated. For this purpose, this article reviews corrosion behavior and structural material compatibility, including ferrous alloys, refractory metals, and ceramics, by liquid Li, PbLi, Sn, Ga, and Hg.

Jun, Jiheon↗
DOE OSTI2024

Residual resistance ratio measurement system for Nb 3 Sn wires extracted from Rutherford cables

Residual resistance ratio (RRR) of superconducting strands is an important parameter for magnet electrical stability. RRR serves as a measure of the low-temperature electrical conductivity of the copper within a conductor that has a copper stabilization matrix. For Nb 3 Sn, due to the need of a reaction heat treatment, the technical requirements for high quality measurements of strands extracted from Rutherford cables are particularly demanding. Quality of wire, cabling deformation, heat treatment temperature, heat treatment atmosphere, sample handling, and measurement methods can all affect the RRR. Therefore, as an integral part of the electrical quality control (QC) of Nb 3 Sn Rutherford cables manufactured at the Lawrence Berkeley National Laboratory, it was prudent that we established a RRR measurement system that can isolate the assessment of cable-fabrication-related impacts from sample preparation and measurement factors. Here we describe a bespoke cryocooler-based measurement system, capable of measuring RRR of over 80 samples in a single cooldown. The samples are mounted on custom-designed printed circuit boards that accommodate the shape of strands extracted from a Rutherford cable without added deformation, which we will show is critical in ensuring that the measurements accurately represent the RRR values of the conductor within the cable. Using this sample mounting solution, we routinely measure the overall RRR of the strand as well as individual intra-strand sections corresponding to both cable edges and cable broad faces with high reproducibility. Such measurements provide valuable information on the variation of RRR along the length of the strands as well as across strand productions and cable runs over time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Interaction of methanol with a layered α-Sn(IV) phosphate on its surface: A solid-state NMR study

Here, a layered crystalline phosphate, α-Sn(HPO 4 ) 2 ·H 2 O, treated with CD 3 OD was characterized by the 31 P, 119 Sn, 1 H and 2 H solid-state NMR techniques. The 2 H solid-echo MAS NMR spectra of the product have unexpectedly revealed deuterated hydronium ions on the surface of this material instead of intercalated methanol. According to the 13 C NMR and GC–MS studies, these ions are formed by water molecules following a dehydration of the methanol-d 4 to yield deuterated dimethyl ether.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Effect of Al substitution on the magnetocaloric properties of Ni-Co-Mn-Sn multifunctional alloys

Ni-Mn-based metamagnetic shape memory alloys have been extensively studied due to their multifunctional properties including magnetocaloric effect (MCE), magnetoresistance effect, and magnetic-field-induced strain. However, the large intrinsic thermal hysteresis of these alloys sets a limit on further development for practical applications. Here, with a few atomic percent Al substitution, we greatly reduced the thermal hysteresis and transformation temperature interval while maintaining the large magnetization difference (ΔM) between austenite and martensite. The simultaneous achievement of a large ΔM and low thermal hysteresis leads to a remarkable enhancement in MCE upon Al substitution, and a maximum magnetic entropy change of 31.6 J/kg K is achieved under a field of 5 T in Ni 39 Co 11 Mn 40 Sn 8 Al 2 . Furthermore, our in situ high-energy X-ray diffraction experiments show that the Ni 39 Co 11 Mn 40 Sn 8 Al 2 has good geometric compatibility between austenite and martensite, which accounts for the reduced thermal hysteresis in this alloy. This study is instructive for the development of high-performance magnetocaloric materials in the metamagnetic shape memory alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High Critical Current Density in Internally-oxidized Nb 3 Sn Superconductors and its Origin

In this paper, we report achievement of non-Cu-matrix critical current density $(J_c)$ in internally-oxidized Nb 3 Sn superconductors that surpasses the best state-of-the-art Nb 3 Sn and the $J_c$ specification of the Future Circular Collider. We then explore the mechanism of the improvement, which was believed to be caused by refined grain size. However, our experiment showed that even with similar grain size, internally-oxidized wires had significantly higher $J_c$ than non-oxidized wires. This, combined with transmission electron microscopy and atom probe tomography studies which showed a high density of intragranular nano-precipitates with suitable sizes as pinning centers in internally-oxidized wires, demonstrates a significant contribution from the nano-precipitates.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Effect of Solvent on the Local Structure, Dynamics, and Vibrational Density of States in Sn-BEA Zeolite

Lewis acid zeolites are attractive catalysts for epoxidation and biomass valorization, as they are highly active and selective in the liquid phase and can operate at or near ambient conditions. While a rich experimental literature exists on liquid-phase Lewis acid zeolite catalysis, our understanding of the molecular organization and solvent dynamics in the vicinity of Lewis acid sites with differing metal site speciation remains limited. In this work, we investigate the molecular coordination and diffusion of two common solvents (methanol and water) around the closed and open Sn-BEA zeolite active sites using molecular dynamics simulations with a machine-learned interatomic potential trained on ab initio molecular dynamics trajectories. Molecular dynamics simulations reveal that introducing active sites significantly enhances local order in the first and second solvation shells compared to the pure silica case. For methanol, both closed and open active sites are singly coordinated, while more than two water molecules coordinate the open site. In contrast to methanol, we observed that water molecules dissociate, leading to the formation of additional Sn-OH and silanol groups away from the active site. The diffusion coefficients of water and methanol are functions of the solvent population in the pore. Here, our work provides insights into how active site speciation in Lewis acid zeolites affects solvent coordination, diffusion, and vibrational signature. This information is foundational for catalyst design and optimization of liquid-phase catalytic processes in zeolites. It also demonstrates the suitability of machine-learned interatomic potentials for modeling reactive systems, enabling sufficiently long trajectories for appropriate statistical averaging.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Intrinsic Formamidinium Tin Iodide Nanocrystals by Suppressing the Sn(IV) Impurities

The long search for non-toxic alternatives to lead halide perovskites (LHPs) has shown that some compelling properties of LHPs, such as low effective masses of carriers, can only be attained in their closest Sn(II) and Ge(II) analogs, despite their tendency to oxidation. Judicious choice of chemistry allowed formamidinium tin iodide (FASnI 3 ) to reach a power conversion efficiency of 14.81% in photovoltaic devices. This progress motivated us to develop a synthesis of colloidal FASnI 3 NCs with a concentration of Sn(IV) reduced to an insignificant level and probe their intrinsic structural and optical properties. Intrinsic FASnI 3 NCs exhibit unusually low absorption coefficients of 4 x 10 3 cm -1 at the first excitonic transition, a 190 meV increase of the bandgap as compared to the bulk material, and a lack of excitonic resonances. These features are attributed to a highly disordered lattice, distinct from the bulk FASnI 3 as supported by structural characterizations and first-principles calculations.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Imaging Ferroelastic Domain Walls in Hybrid Improper Ferroelectric Sr 3 Sn 2 O 7

For this work, we combined synchrotron-based near field infrared spectroscopy and atomic force microscopy to image the properties of ferroelastic domain walls in Sr 3 Sn 2 O 7 . Although frequency shifts at the walls are near the limit of our sensitivity, we can confirm semiconducting rather than metallic character and widths between 20 and 60 nm. The latter is significantly narrower than in other hybrid improper ferroelectrics like Ca 3 Ti 2 O 7 . We attribute this trend to the softer lattice in Sr 3 Sn 2 O 7 , which may enable the octahedral tilt and rotation order parameters to evolve more quickly across the wall without significantly increased strain. These findings are crucial for the understanding of phononic properties at interfaces and the development of domain wall-based devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Real-Time Investigation of Sn(II) Oxidation in Pb-Free Halide Perovskites by X-ray Absorption and Mössbauer Spectroscopy

Sn(II) halide perovskites are a less toxic alternative to Pb-based materials in perovskite solar cells, but oxidation to Sn(IV) introduces additional degradation pathways. Improving stability requires mechanistic pictures of O 2 - and H 2 O-induced degradation and their synergy. In this work, we demonstrate that X-ray absorption spectroscopy reports the average valency of the bulk material, allowing oxidation kinetics to be measured from minutes to days. Optical and X-ray diffraction studies demonstrate the challenge of isolating oxidative degradation with techniques lacking element specificity and oxidation state sensitivity. Finally, 119Sn Mössbauer spectroscopy is presented as a lab-based technique capable of providing information on valency and speciation throughout oxidation.

14 SOLAR ENERGY↗
DOE OSTI2020

Room-temperature terahertz anomalous Hall effect in Weyl antiferromagnet Mn 3 Sn thin films

Antiferromagnetic spin motion at terahertz (THz) frequencies attracts growing interests for fast spintronics, however, their smaller responses to external field inhibit device application. Recently the noncollinear antiferromagnet Mn 3 Sn, a Weyl semimetal candidate, was reported to show large anomalous Hall effect (AHE) at room temperature comparable to ferromagnets. Dynamical aspect of such large responses is an important issue to be clarified for future THz data processing. Here the THz anomalous Hall conductivity in Mn 3 Sn thin films is investigated by polarization-resolved spectroscopy. Large anomalous Hall conductivity Re σxyð Þ ω 20 Ω1cm1 at THz frequencies is clearly observed as polarization rotation. A peculiar temperature dependence corresponding to the breaking/recovery of symmetry in the spin texture is also discussed. Observation of the THz AHE at room temperature demonstrates the ultrafast readout for the antiferromagnetic spintronics using Mn3Sn, and will also open new avenue for studying nonequilibrium dynamics in Weyl antiferromagnets.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Localized spin-orbit polaron in magnetic Weyl semimetal Co 3 Sn 2 S 2

The kagome lattice Co 3 Sn 2 S 2 exhibits the quintessential topological phenomena of a magnetic Weyl semimetal such as the chiral anomaly and Fermi-arc surface states. Probing its magnetic properties is crucial for understanding this correlated topological state. Here, using spin-polarized scanning tunneling microscopy/spectroscopy (STM/S) and non-contact atomic force microscopy (nc-AFM) combined with first-principle calculations, we report the discovery of localized spin-orbit polarons (SOPs) with three-fold rotation symmetry nucleated around single S-vacancies in Co 3 Sn 2 S 2. The SOPs carry a magnetic moment and a large diamagnetic orbital magnetization of a possible topological origin associated relating to the diamagnetic circulating current around the S-vacancy. Appreciable magneto-elastic coupling of the SOP is detected by nc-AFM and STM. Our findings suggest that the SOPs can enhance magnetism and more robust time-reversal-symmetry-breaking topological phenomena. Controlled engineering of the SOPs may pave the way toward practical applications in functional quantum devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Softening of a flat phonon mode in the kagome ScV 6 Sn 6

Geometrically frustrated kagome lattices are raising as novel platforms to engineer correlated topological electron flat bands that are prominent to electronic instabilities. Here, we demonstrate a phonon softening at the k z = π plane in ScV 6 Sn 6 . The low energy longitudinal phonon collapses at ~98 K and q = $\tfrac{1}{3}$ $\tfrac{1}{3}$ $\tfrac{1}{2}$ due to the electron-phonon interaction, without the emergence of long-range charge order which sets in at a different propagation vector q CDW = $\tfrac{1}{3}$ $\tfrac{1}{3}$ $\tfrac{1}{3}$. Theoretical calculations corroborate the experimental finding to indicate that the leading instability is located at $\tfrac{1}{3}$ $\tfrac{1}{3}$ $\tfrac{1}{2}$ of a rather flat mode. We relate the phonon renormalization to the orbital-resolved susceptibility of the trigonal Sn atoms and explain the approximately flat phonon dispersion. Our data report the first example of the collapse of a kagome bosonic mode and promote the 166 compounds of kagomes as primary candidates to explore correlated flat phonon-topological flat electron physics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Plethora of tunable Weyl fermions in kagome magnet Fe 3 Sn 2 thin films

Interplay of magnetism and electronic band topology in unconventional magnets enables the creation and fine control of novel electronic phenomena. In this work, we use scanning tunneling microscopy and spectroscopy to study thin films of a prototypical kagome magnet Fe 3 Sn 2 . Our experiments reveal an unusually large number of densely-spaced spectroscopic features straddling the Fermi level. These are consistent with signatures of low-energy Weyl fermions and associated topological Fermi arc surface states predicted by theory. By measuring their response as a function of magnetic field, we discover a pronounced evolution in energy tied to the magnetization direction. Electron scattering and interference imaging further demonstrates the tunable nature of a subset of related electronic states. Our experiments provide a direct visualization of how in-situ spin reorientation drives changes in the electronic density of states of the Weyl fermion band structure. Combined with previous reports of massive Dirac fermions, flat bands, and electronic nematicity, our work establishes Fe 3 Sn 2 as an interesting platform that harbors an extraordinarily wide array of topological and correlated electron phenomena.

36 MATERIALS SCIENCE↗