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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Pressure-induced tuning of the triangular-honeycomb structure of ferroelectric quantum spin liquid candidate, TbInO 3

The pressure response of the triangular-honeycomb-structured quantum spin liquid candidate, TbInO 3 , has been determined via neutron powder diffraction up to 5.75(5) GPa. The system retains hexagonal symmetry up to the maximum pressure considered. The structure was found to compress less anisotropically than related compounds, though it is more compressible within the 2D plane than between subsequent layers. Through extracting the O-atom coordinates we find experimental evidence that may suggest the enhancement of ferroelectricity at pressures as low as 3 GPa.

Ridley, Christopher J. [Oak Ridge National Laborat↗
DOE OSTI2026

Contrasting structural reversibility and magnetic correlations in isostructural honeycomb magnets CrCl3 and 𝛼−RuCl3

We report a comparative neutron single crystal diffraction study of the structural and magnetic properties of layered halides CrCl3 and 𝛼−RuCl3. They host a honeycomb arrangement of transition metal ions with distinct electronic configurations and undergo a first-order structural transition between high-temperature 𝐶⁢2/𝑚 and low-temperature 𝑅⁢‾‾‾3. Both compounds show a step-like change in the 𝑐-lattice parameter across the structure transition. In contrast, the in-plane lattice response is quite different: 𝛼−RuCl3 exhibits an abrupt hysteretic change across the transition accompanied by progressive crystalline degradation upon thermal cycling, whereas CrCl3 shows a smooth in-plane lattice evolution and remains structurally robust. Magnetically, CrCl3 orders into an A-type antiferromagnetic structure at 𝑇𝑁=14 K and exhibits pronounced diffuse magnetic scattering extending up to about 40 K. 𝛼−RuCl3 shows no observable magnetic diffuse scattering above its zigzag antiferromagnetic ordering temperature 𝑇𝑁=7.6 K. These results suggest that the contrasting structural responses arise from an interplay between interlayer sliding energetics, stacking-strain coupling, and elastic accommodation of the stacking transition. The distinct chemical bonding and electronic configurations of the two compounds provide a microscopic basis for their different lattice responses to the structure transition and magnetic correlations.

Morgan, Zachary [ORNL] (ORCID:0000000243625911)↗
DOE OSTI2024

Field-dependent magnons in the honeycomb antiferromagnet CoTiO 3

We report field-dependent high-resolution inelastic neutron scattering (INS) measurements on the honeycomb lattice magnet, CoTiO 3 , to study the evolution of its magnon excitations across a spin reorientation transition driven by an in-plane magnetic field. By carrying out elastic neutron scattering in a magnetic field, we show that the sample transitions from a collinear antiferromagnetic state with multiple magnetic domains at a low field to a monodomain state with a canted magnetic structure at a high field. Concurrent with this transition, we observed significant changes in both the energy and the width of the zone center magnon peak. The observed width change was argued to be consistent with an unusual zero-field state with extended domain walls. On the other hand, the magnon spectra near the K point of the Brillouin zone boundary were found to be largely insensitive to the changes in the ordered moment directions and the domain configuration. We argue that this observation is difficult to explain within the framework of the bond-dependent model proposed in a recent INS study [M. Elliot et al., Nat. Commun. 12, 3936 (2021)]. Our paper therefore calls for alternative explanations for the observed K-point gap in CoTiO 3 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Topological and magnetic properties of a noncollinear spin state on a honeycomb lattice in a magnetic field

Here, this paper studies the topological and magnetic properties of a noncollinear spin state on a honeycomb lattice that evolves from coplanar to ferromagnetic with a magnetic field applied along the z axis. The coplanar state is stabilized by nearest-neighbor ferromagnetic interactions, single-ion anisotropy along z, and DzyaloshinskiiMoriya interactions between next-nearest-neighbor sites. Below the critical field H$_c$ that aligns the spins, the magnetic unit cell contains six sites and the spin dynamics contains six magnon modes. Although the classical energy is degenerate with respect to the twist angle φ between nearest-neighbor spins, the dependence of the free energy on φ at low temperatures is dominated by the magnon zero-point energy, which contains extremum at φ = πl/3 for integer l. The only unique ground states GS(φ) have l = 0 or 1. For H < H$'_c$, the zero-point energy has minima at even l and the ground state is GS(0); for H$'_c$ < H < H$'_c$, the zero-point energy has minima at odd l and the ground state is GS(π/3). In GS(0), the magnon density of states exhibits five distinct topological phases with increasing field associated with the opening and closing of energy gaps between two or three magnonic bands. While the Berry curvature vanishes for the coplanar φ = 0 phase in zero field, the Berry curvature and Chern numbers exhibit signatures of the five topological phases below H$'_c$. Whereas the Berry curvature and Chern number are sensitive to changes in the magnon density of states within GS(π/3), the inelastic spectrum S(k,ω) is sensitive to changes in the intensity of the magnon modes in the different magnetic phases GS(0) and GS(π/3) rather than the five topological phases within GS(π/3).

Fishman, Randy S. [Oak Ridge National Laboratory (↗
DOE OSTI2024

Probing Majorana Wave Functions in Kitaev Honeycomb Spin Liquids with Second-Order Two-Dimensional Spectroscopy

Two-dimensional coherent terahertz spectroscopy (2DCS) emerges as a valuable tool to probe the nature, couplings, and lifetimes of excitations in quantum materials. It thus promises to identify unique signatures of spin liquid states in quantum magnets by directly probing properties of their exotic fractionalized excitations. Here, in this study, we calculate the second-order 2DCS of the Kitaev honeycomb model and demonstrate that distinct spin liquid fingerprints appear already in this lowest-order nonlinear response $\chi^{(2)}_{yzx}$⁡($ω_1$, $ω_2$) when using crossed light polarizations. We further relate the off-diagonal 2DCS peaks to the localized nature of the matter Majorana excitations trapped by $\mathbb{Z}_2$ flux excitations and show that 2DCS thus directly probes the inverse participation ratio of Majorana wave functions. By providing experimentally observable features of spin liquid states in the 2D spectrum, our Letter can guide future 2DCS experiments on Kitaev magnets.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Magnetic dynamics in NiTiO 3 honeycomb antiferromagnet using neutron scattering

The ilmenite NiTiO 3 consists of a buckled honeycomb lattice, with the Ni spins aligned ferromagnetically in-plane and antiferromagnetically out-of-plane. Using neutron spectroscopy, the magnetic structure and the dynamics were investigated as a function of temperature. Dispersive acoustic bands and nearly dispersionless optical bands at ≈ 3.7 meV are described by a highly anisotropy Heisenberg model with stronger antiferromagnetic (AFM) out-of-plane, weaker ferromagnetic (FM) in-plane interactions and an anisotropy gap of 0.95 meV. Furthermore, the order parameter yields a critical exponent between the Heisenberg and two-dimensional Ising models, consistent with highly anisotropic Heisenberg systems. The frustration parameter ≈ 2 supports a weakly frustrated system.

Antiferromagnets↗
DOE OSTI2026

Tunable magnetic excitations in the honeycomb antiferromagnet (Co,Ni)⁢TiO3

The solid solution of the honeycomb antiferromagnet (AFM) Co0.5⁢Ni0.5⁢TiO3 (CNTO) was synthesized by mixing a 1:1 molar ratio of CoTiO3 (CTO) and NiTiO3 (NTO). Powder neutron scattering was used to determine the structure and magnetic spectrum, where the nuclear and magnetic structures resemble those of the end members. The Néel temperature (T𝑁 = 27 ± 1 K), the ordered magnetic moment (M = 2.29 ± 0.03 𝜇𝐵 per magnetic ion), and lattice parameters are intermediate between those of the two. From inelastic neutron scattering, it is observed that the magnon density of states (MDOS) extends up to 13 meV, and the interaction can be described by an XXZ-type magnetic Hamiltonian. Above 15 meV, spin-orbit excitons (SOEs) are observed similarly to those in CTO, but with modified spin-orbit crystal-field splitting because of the substitution of Ni at Co sites, and the disorder induced by the Ni substitution modifies the spin-orbit crystal field. Thus, the magnetic dynamics of the CNTO cannot be described as a simple average of the two parent compounds.

Rathnayaka, Srimal [University of Virginia, Charlo↗
DOE OSTI2025

Magnetoelastic-coupling-assisted first-order antiferromagnetic transitions in the corrugated honeycomb-lattice compounds (Ca, Sr) ⁢Mn 2 ⁢ P 2

Understanding the origin of unconventional magnetic order is a central theme in the research field of functional quantum materials for spin-dependent applications. In general, a paramagnetic (PM) to antiferromagnetic (AFM) transition is of thermodynamically second order in nature in the absence of a magnetic field. In the magnetically frustrated corrugated-honeycomb lattice compounds (Ca, Sr) ⁢Mn 2 ⁢ P 2 , electrical resistivity 𝜌 measurements in the 𝑎⁢𝑏 plane are reported to exhibit sharp discontinuities at the respective PM to AFM ordering temperatures 𝑇 N = 69.5 and 53 K, respectively, signifying the unusual first-order nature of the AFM transition. To reveal the origin of such anomalous transitions, high-resolution linear thermal-expansion measurements are reported for both CaMn 2 ⁢P 2 and SrMn 2 ⁢ P 2 in the 𝑎⁢𝑏 plane and along the 𝑐 axis using capacitance dilatometry. The thermal expansion measurements show a sharp discontinuity in Δ⁢𝐿/𝐿 at 𝑇 N , yielding a diverging behavior in the thermal expansion coefficient 𝛼⁡(𝑇) associated with strong magnetoelastic coupling, driving the first-order AFM transition in CaMn 2 ⁢P 2 . However, this effect is weaker in SrMn 2 ⁢P 2 , consistent with the magnetic entropy changes 𝑆⁡(𝑇) obtained from the heat-capacity measurements. Temperature-dependent 𝑎⁢𝑏-plane x-ray diffraction measurements for CaMn 2 ⁢ P 2 near its 𝑇 N yield a volume thermal expansion coefficient consistent with literature data for other materials. The uniaxial pressure derivatives of 𝑇 N in the two compounds are found to be respectively opposite in sign, presumably due to the different magnetic structures.

Pakhira, Santanu [Maulana Azad National Institute ↗
DOE OSTI2025

Quantum stabilization of unexpected ordered phases on the honeycomb lattice

In this work, I discuss and showcase the utility of the method called minimally-augmented spin-wave theory (MAGSWT) as a relatively simple semi-analytical approach to the phase diagrams of quantum magnets. It complements numerical methods by providing physical insight into which states are competitive and by yielding approximate phase boundaries that agree well with much more numerically intensive calculations. This approach enabled me to construct the faithful phase diagrams of two paradigmatic honeycomb-lattice models in the quantum S=1/2 limit, the J 1 –J 3 FM-AF and J 1 –J 2 AF models, for the collinear quantum phases that replace or extend the classical ones. The results are in good qualitative and semi-quantitative agreement with state-of-the-art numerical studies for these models, correctly capturing the emergence of unexpected quantum phases and the suppression of classically favored spiral orders by quantum fluctuations. This study provides a much-needed important guidance to the ongoing theoretical and experimental searches of the unconventional quantum states. This work will be of significant and timely interest to both theorists and experimentalists in the field of quantum magnetism, broadly defined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

High-resolution neutron diffraction determination of noncollinear antiferromagnetic order in the honeycomb magnetoelectric Fe 4 ⁢Nb 2⁢ O 9

Magnetoelectric systems offer potential for device applications exploiting coupled states between electric and magnetic properties. Among magnetoelectric materials, Fe 4 ⁢Nb 2 ⁢O 9 has attracted special attention because of its pronounced dielectric signal at high magnetic transition temperatures. However, the magnetic ground state, which is essential information for understanding its unusual magnetoelectricity, remains unclarified. Here, we report a noncollinear magnetic ground state of Fe 4 ⁢Nb 2 ⁢O 9 . To examine the magnetoelectric effect associated with sequential magnetic and structural transitions upon cooling, we conducted combined x-ray diffraction, magnetic susceptibility, magnetization, dielectric constant, and magnetodielectric experiments. Powder neutron diffraction experiments revealed a series of magnetic Bragg peaks and clear splitting of peaks via structural transition. Magnetic Rietveld refinements, combined with group theory analysis, determined a noncollinear antiferromagnetic structure including a significant 𝑐-axis moment component at 1.5 K. This article provides insights into the understanding of its magnetoelectric properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Evidence for field induced quantum spin liquid behavior in a spin-1/2 honeycomb magnet

One of the most important issues in modern condensed matter physics is the realization of fractionalized excitations, such as the Majorana excitations in the Kitaev quantum spin liquid. To this aim, the 3d-based Kitaev material Na 2 Co 2 TeO 6 is a promising candidate whose magnetic phase diagram of B // a* contains a field-induced intermediate magnetically disordered phase within 7.5 T < |B| < 10 T. The experimental observations, including the restoration of the crystalline point group symmetry in the angle-dependent torque and the coexisting magnon excitations and spinon-continuum in the inelastic neutron scattering spectrum, provide strong evidence that this disordered phase is a field induced quantum spin liquid with partially polarized spins. Our variational Monte Carlo simulation with the effective K-J 1 -Γ-Γ'-J 3 model reproduces the experimental data and further supports this conclusion.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ultra‐Flexible Pixelated Perovskite Photodetectors Enabled by Honeycomb Polymer Grids for High‐Resolution Imaging

Abstract A nature‐inspired fabrication method based on a photolithography‐free flexible polymer grid is reported for high‐resolution pixelation of perovskite photodiode arrays with exceptional mechanical ductility and a morphology resembling that of natural compound eyes. The resulting pixelated perovskite photosensitive layer has a ≈1 µm pixel size with 2000 Pixels per inch (PPI) resolution when fully assembled as a photodetector array, delivering a detectivity of >10 13 Jones while providing cross‐talk free imaging. Using a polymer grid effectively releases stress on the perovskite platform, greatly increasing the mechanical agility of the otherwise brittle perovskite film. This novel fabrication methodology and device design offer new possibilities for applications in robotics, biomedical imaging, and virtual and augmented reality.

Zheng, Ding [Department of Chemistry and the Mater↗
DOE OSTI2025

Continuum of magnetic excitations in the Kitaev honeycomb iridate D 3 LiIr 2 O 6

Inelastic neutron scattering (INS) measurements of powder D 3 ( 7 Li)( 193 Ir) 2 O 6 reveal low energy magnetic excitations with a scattering cross-section that is broad in ∣Q∣ and energy transfer. The magnetic nature of the excitation spectrum is demonstrated by longitudinally polarized neutron scattering. The total magnetic moment of 1.8(4)μ B /Ir inferred from the observed magnetic scattering cross-section is consistent with the effective moment inferred from magnetic susceptibility data and expectations for the J eff = 1/2 single ion state. The rise in the dynamic correlation function $\mathcal{S}(Q,w)$ for ℏω < 5 meV can be described by a simple model assuming nearest-neighbor anisotropic spin exchange, such as that found in the Kitaev model. Exchange disorder associated with the D site likely plays an important role in stabilizing the low T quantum fluctuating state.

Halloran, Thomas [Johns Hopkins Univ., Baltimore, ↗
DOE OSTI2024

Dimensionality crossover to a two-dimensional vestigial nematic state from a three-dimensional antiferromagnet in a honeycomb van der Waals magnet

The effects of fluctuations and disorder, which are substantially enhanced in reduced dimensional-ities, can play a crucial role in producing nontrivial phases of matter such as vestigial orders char-acterized by a composite order parameter. However, fluctuation-driven magnetic phases in low dimensions have remained relatively unexplored. Here we demonstrate a phase transition from the zigzag antiferromagnetic order in the three-dimensional bulk to a Z 3 vestigial Potts-nematicity in two-dimensional few-layer samples of van der Waals magnet NiPS 3 . Our spin relaxometry and op-tical spectroscopy measurements reveal that the spin fluctuations are enhanced over the gigahertz to terahertz range as the layer number of NiPS 3 reduces. Monte Carlo simulations corroborate the experimental finding of 3-fold rotational symmetry breaking, but show that translational symmetry is restored in thin layers of NiPS 3 . Furthermore, our results show that strong quantum fluctuations can stabilize an unconventional magnetic phase after destroying a more conventional one.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Static magnetic order with strong quantum fluctuations in spin-1/2 honeycomb magnet Na 2 Co 2 TeO 6

Kitaev interactions, arising from the interplay of frustration and bond anisotropy, can lead to strong quantum fluctuations and, in an ideal case, to a quantum-spin-liquid state. However, in many nonideal materials, spurious non-Kitaev interactions typically promote a zigzag antiferromagnetic order in the d-orbital transition-metal compounds. Here, by combining neutron scattering with muon-spin rotation and relaxation techniques, we provide mechanism insights into the exotic properties of Na 2 Co 2 TeO 6 , a candidate material of the Kitaev model. Below T N , the zero-field muon-spin relaxation rate becomes almost constant (~0.45 μs –1 ). We attribute this temperature-independent relaxation rate to the strong quantum fluctuations, as well as to the frustrated Kitaev interactions. As the magnetic field increases, neutron scattering data indicate a broader spin-wave excitation at the K-point. Therefore, quantum fluctuations seem not only robust but are even enhanced by the applied magnetic field. Our findings provide valuable hints for understanding the onset of the quantum-spin-liquid state in Kitaev materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Electronic structure of the honeycomb iridate Cu 2 ⁢IrO 3 at high pressure

Cu 2 IrO 3 has attracted recent interest due to its proximity to the Kitaev quantum spin liquid state and the complex structural response observed at high pressures. We use x-ray spectroscopy and scattering as well as electrical transport techniques to unveil the electronic structure of Cu 2 IrO 3 at ambient and high pressures. Despite featuring a Ir 4+ J eff = 1/2 state at ambient pressure, Ir L 3 -edge resonant inelastic x-ray scattering reveals broadened electronic excitations that point to the importance of Ir 5d-Cu 3d interaction. High pressure first drives an Ir-Ir dimer state with collapsed < L · S > and < L z >/< S z >, signaling the formation of 5d molecular orbitals. A novel Cu → Ir charge transfer is observed above 30 GPa at low temperatures, leading to an approximate Ir 3+ and Cu 1.5+ valence, with persistent insulating electrical transport seemingly driven by charge segregation of Cu 1+ /Cu 2+ ions into distinct sites. Concomitant x-ray spectroscopy and diffraction measurements through different thermodynamic paths demonstrate a strong electron-lattice coupling, with J eff = 1/2 and Ir 3+ /Cu 1.5+ electronic states occurring only in phases 1 and 5, respectively. Remarkably, the charge-transfer state can only be reached if Cu 2 IrO 3 is pressurized at low temperature, suggesting that phonons play an important role in the inhibiting this phase. Furthermore, these results point to the choice of thermodynamic path across interplanar collapse transition as a key parameter to access novel states in intercalated iridates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Nanoporous Wood Chips Based Sizable, Robust, and Low-Cost Honeycomb Vacuum Insulation Panels (DOE BENEFIT Final Research Performance Progress Report (RPPR))

Conventional vacuum insulation panels (VIPs) suffer from severe limitations including high cost, vulnerability to perforation, and significant performance degradation over time due to vacuum loss. InventWood Inc. (IW) and partnering teams completely re-engineered the VIP structure by constructing arrays of isolated vacuum-cells to enable limited cutting at designated areas (in between vacuum cells) and reduced consequential vacuum loss due to puncture. The teams also replaced the expensive vacuum insulation core materials with a low-cost commercial wood pulp and recycled long fiber. The wood pulp derived VIP can deliver an overall panel insulation of R15 (<0.01W/m·K) with over 90% thermal resistance retention after cutting (R13.5 overall, R5 along the cut edges). In addition, the vacuum-cell-array design minimizes edge losses, resulting in more durable performance, longer service life (>50 years), and higher R-value per dollar towards a cost target of <$1/ft 2 ·in. It is anticipated that the Nanochip-VIP will attract strong market interest and become an affordable insulation solution for energy efficient buildings and retrofits, leading to significant reductions in energy usage.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗