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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Block-Type Antiferromagnetism in Single Chain Quasi-One-Dimensional K 3 ⁢Fe 2 ⁢Se 4

One-dimensional (1D) structures provide a unique platform to study the correlated quantum interactions and phase transitions such as unconventional magnetism and superconducting states. Here, we report that iron chalcogenide K 3 ⁢Fe 2 ⁢Se 4 exhibits an unusual block-type canted antiferromagnetic (AFM) order with a clear single chain quasi-1D structure, which is structurally different from the two-leg ladder BaFe 2 ⁢Se 3 , through both experimental measurements and density matrix renormalization group (DMRG) calculations. The narrow bandgap semiconductor K 3 ⁢Fe 2 ⁢Se 4 has a quasi-1D edge-shared FeSe4 tetrahedra chain structure and orders antiferromagnetically below 110 K. The magnetic moments couple antiferromagnetically along the quasi-1D chain direction of the 𝑏 axis and form an up-down-down-up (↑−↓−↓−↑)–like spin structure with a commensurate propagation vector 𝒌=⁢(0,0,0), where block-type spin ↑−↑ or ↓−↓ coupling are between the longer Fe-Fe bonds of the quasi-1D chain. DMRG results show that block antiferromagnetic state is stable in K 3 ⁢Fe 2 ⁢Se 4 and reveal that the block-ordered arrangement of Fe 2.5+ ions spins arise from the competition between ferromagnetic and AFM interaction in the presence of strong electronic correlation. Our research results not only report the discovery of a clear block-type canted antiferromagnetic structure in a real quasi-1D chain material but also provide a theoretical approach to understand the block-type antiferromagnetism in quasi-1D iron chalcogenides.

antiferromagnetism↗
DOE OSTI2020

First-principles calculation of spin and orbital contributions to magnetically ordered moments in Sr 2 IrO 4

Here, we show how an accurate first-principles treatment of the canted-anti-ferromagnetic ground state of Sr 2 IrO 4 , a prototypical 5d correlated spin-orbit coupled material, can be obtained without invoking any free parameters, such as the Hubbard $\textit{U}$ or tuning the spin-orbit coupling strength. Our theoretically predicted iridium magnetic moment of 0.250$μ_B$, canted by 12.6° off the $\textit{a}$ axis, is in accord with experimental results. By resolving the magnetic moments into their spin and orbital components, we show that our theoretically obtained variation of the magnetic scattering amplitude $\langle M_m \rangle$ as a function of the polarization angle is consistent with recent nonresonant magnetic x-ray scattering measurements. The computed value of the band gap (55 meV) is also in line with the corresponding experimental values. A comparison of the band structure to that of the cuprates suggests the presence of incommensurate charge-density wave phases in Sr 2 IrO 4 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Noncollinear magnetic structure and magnetoelectric coupling in buckled honeycomb Co 4 Nb 2 O 9 : A single-crystal neutron diffraction study

Through an analysis of single-crystal neutron diffraction data, we present the magnetic structure and magnetoelectric properties of Co 4 Nb 2 O 9 under various magnetic fields. In zero field, neutron diffraction experiments below T N =27K reveal that the Co 2+ moments order in the (ab) plane without any spin canting along the c axis, manifested by the magnetic symmetry C2/c'. Along each Co chain parallel to the c axis, the moments of nearest-neighbor Co atoms order ferromagnetically with a small cant away from the next-nearest-neighbor Co moments. Under the applied magnetic field H ∥ a, three magnetic domains were aligned with their major magnetic moments perpendicular to the magnetic field with no other observable magnetic transitions. The influences of magnetic fields on the magnetic structures associated with the observed magnetoelectric coupling are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Magnetic structure and multiferroicity of Sc-substituted hexagonal YbFeO 3

The hexagonal rare-earth ferrite RFeO 3 family represents a unique class of multiferroics exhibiting weak ferromagnetism, and a strong coupling between magnetism and structural trimerization is predicted. However, the hexagonal structure for RFeO 3 remains metastable in conventional conditions. We have succeeded in stabilizing the hexagonal structure of polycrystalline YbFeO 3 by partial Sc substitution of Yb. Using bulk magnetometry and neutron diffraction, we find that Yb 0.42 Sc 0.58 FeO 3 orders into a canted antiferromagnetic state with the Néel temperature T N ~ 165K, below which the Fe 3+ moments form the triangular configuration in the ab plane and their in-plane projections are parallel to the [100] axis, consistent with magnetic space group P6 3 c'm'. It is determined that the spin canting is aligned along the c axis, giving rise to the weak ferromagnetism. Furthermore, the Fe 3+ moments reorient toward a new direction below reorientation temperature T R ~ 40K, satisfying magnetic subgroup P6 3 , while the Yb 3+ moments order independently and ferrimagnetically along the c axis at the characteristic temperature T Yb ~ 15K. Interestingly, reproducible modulation of electric polarization induced by magnetic field at low temperature is achieved, suggesting that the delicate structural distortion associated with two-up/one-down buckling of the Yb/Sc planes and tilting of the FeO 5 bipyramids may mediate the coupling between ferroelectric and magnetic orders under magnetic field. Furthermore, the present work represents substantial progress to search for high-temperature multiferroics in hexagonal ferrites and related materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Thermal Hall effect in the Kitaev-Heisenberg system with spin-phonon coupling

Motivated by the giant phonon anomalies in α-RuCl3 reported by H. Li et al. [Nat. Commun. 12, 3513 (2021)], we investigate the thermal Hall effect in a Kitaev-Heisenberg system in the presence of the coupling between spins and phonons arising from chlorine atoms' vibration. We observe that the coupling modifies the relative stability between different magnetic states under a magnetic field, especially stabilizing a canted zigzag antiferromagnetic state. Remarkably, the spin-phonon interaction has distinct effects on the thermal Hall conductivity in different magnetically ordered states. For a canted zigzag state, which is relevant to α-RuCl3, the spin-phonon interaction enhances the magnon excitation gap induced by a magnetic field and suppresses the thermal Hall conductivity at low temperatures. For the Kitaev spin liquid state, we find that the spin-phonon interaction reduces the excitation gap of Majorana fermions and destabilizes the quantized thermal Hall effect. Our results demonstrate a crucial role of phonon degrees of freedom in the thermal Hall effect in Kitaev materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Introducing the monoclinic polymorph of the honeycomb magnet Na 2 Co 2 TeO 6

Recent theoretical studies have suggested that the low-energy Hamiltonian of honeycomb cobaltate systems could be dominated by anisotropic Kitaev interactions. Motivated by the theory, a honeycomb layered material Na 2 Co 2 TeO 6 with a hexagonal unit cell has been studied and found to exhibit antiferromagnetic (AFM) ordering at 27 K with two spin reorientation transitions at 15 and 5 K. Here we report a monoclinic polymorph of Na 2 Co 2 TeO 6 , also with honeycomb layered structure but with a single AFM transition at 9.6 K and without spin reorientation transitions at lower temperatures. Here, using neutron diffraction, we identify an in-plane zigzag AFM order in the ground state with the spins canted out of the honeycomb planes and ferromagnetically coupled between them. The zigzag order is suppressed by a magnetic field of 6T. The lower critical temperature and field, positive Curie-Weiss temperature, and out-of-plane canting of spins in the monoclinic Na 2 Co 2 TeO 6 suggest enhanced frustration in this polymorph compared to the hexagonal one.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Anomalous temperature-dependent magnetization in the nearly collinear antiferromagnet Y 2 Co 3

Y 2 Co 3 is a newly discovered antiferromagnetic (AFM) compound with distorted kagome layers. Here, previous investigations via bulk magnetization measurements suggested a complex non-collinear magnetic behavior, with magnetic moments primarily anti-aligned along the b axis and some canting towards the ac plane. In this study, we report the magnetic structure of Y 2 Co 3 to be an A-type AFM structure with ferromagnetic (FM) interactions within the distorted kagome plane and an inter-plane antiferromagnetic interaction, as determined by single crystal neutron diffraction. The magnetic moments align along the b axis, with minimal canting towards the c axis, at odds with the previous interpretation of bulk magnetization measurements. The magnetic moments on the two distinct Co sites are (0, -0.68, 0) μB and (0, 1.25, 0.07) μ B . We attribute the previously reported ”non-collinear” behavior to the considerable temperature dependence of itinerant AFM exchange interactions, induced by thermal contraction along the b axis. Additionally, our examination of lattice constants through pressure studies reveals compensating effects on FM and AFM interactions, resulting in negligible pressure dependence of T N .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Magnetic field induced antiferromagnetic cone structure in multiferroic BiFeO 3

Neutron diffraction measurements were performed under high magnetic fields up to 17 T in a multiferroic BiFeO 3 single crystal, in which an intermediate magnetic (IM) phase has been found between the cycloid and canted antiferromagnetic phases [S. Kawachi et al., Phys. Rev. Mater. 1, 024408 (2017)]. We clearly found that the incommensurate magnetic peaks, which split perpendicular to the magnetic field in the cycloid phase, rotate by 90 deg to align parallel to the field in the IM phase. The magnetic structure in the IM phase can be best described by an antiferromagnetic cone (AF cone) structure. The transition from the cycloid to AF cone is of first order and the direction of the magnetic wave vector and the easy plane of the cycloidal component are rotated by 90 deg without changing the cycloidal modulation period, whereas the transition from the AF cone to canted antiferromagnetic phase is gradual and the cone angle becomes smaller gradually without changing the modulation period. Interestingly, the cycloidal component as well as the cone angle in the IM phase shows a large hysteresis between the field increasing and decreasing processes. Finally, this result, combined with the magnetostriction with a large hysteresis previously reported in the IM phase, suggests a strong magnetoelastic coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Successive magnetic orderings in the Ising spin chain magnet DyNi 5 Ge 3

In this report, we investigated a new rare-earth-based one-dimensional Ising spin chain magnet DyNi 5 Ge 3 by means of magnetization, specific heat, and powder neutron diffraction measurements. Due to the crystalline electrical field splitting, the magnetic Dy ions share an Ising-like ground doublet state. Owning to the local point symmetry, these Ising moments form into two canted magnetic sublattices, which were further confirmed by the angle-dependent magnetization measurement. In zero fields, two successive antiferromagnetic phase transitions were found at temperatures T N1 =6K and T N2 =5K, respectively. Only part of the moments are statically ordered in this intermediate state between T N1 and T N2 . Powder neutron diffraction experiments at different temperatures were performed as well. Further, an incommensurate magnetic propagation vector of k m =(0.5,0.4,0.5) was identified. The refined spin configurations through the irreducible representation analysis confirmed that these Ising spins are canted in the crystal ab plane.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High-throughput determination of Hubbard $U$ and Hund $J$ values for transition metal oxides via the linear response formalism

DFT+U provides a convenient, cost-effective correction for the self-interaction error (SIE) that arises when describing correlated electronic states using conventional approximate density functional theory (DFT). The success of a DFT+U(+J) calculation hinges on the accurate determination of its Hubbard U and Hund J parameters, and the linear response (LR) methodology has proven to be computationally effective and accurate for calculating these parameters. This study provides a high-throughput computational analysis of the U and J values for transition metal d-electron states in a representative set of over 1000 magnetic transition metal oxides (TMOs), providing a frame of reference for researchers who use DFT+U to study transition metal oxides. In order to perform this high-throughput study, an ATOMATE workflow is developed for calculating U and J values automatically on massively parallel supercomputing architectures. Here, to demonstrate an application of this workflow, the spin-canting magnetic structure and unit cell parameters of the multiferroic olivine LiNiPO4 are calculated using the computed Hubbard U and Hund J values for Ni-d and O-p states, and are compared with experiment. Both the Ni-d U and J corrections have a strong effect on the Ni-moment canting angle. Additionally, including a O-pU value results in a significantly improved agreement between the computed lattice parameters and experiment

36 MATERIALS SCIENCE↗
DOE OSTI2024

A Nonintrusive Optical Approach to Characterize Heliostats in Utility-Scale Power Tower Plants: Camera Position Sensitivity Analysis

Optics plays a major role in the effectiveness of concentrating solar power (CSP) technologies. The nonintrusive optical (NIO) approach developed by the National Renewable Energy Laboratory uses uncrewed aircraft system (UAS)-based imaging to survey heliostats in a commercial-scale power tower CSP plant and characterize their optical errors. The image processing algorithm uses photogrammetry to calculate the camera position for each image frame, and the accuracy of the estimated optical errors is highly sensitive to the calculated camera position accuracy. In this study, we simulate a series of case studies in python to examine the impact of different parameters of the sensitivity of the camera calculation, including the number of facet corners used as control points for the photogrammetric calculation, precision error in the detected pixel locations of the facet corners in the image, and precision error of the canting and mounting positions of the facets of the heliostat. The case studies consider heliostat geometry based on three commercial designs to serve as representative examples of different possible sizes of heliostats that the NIO method could be applied to. The results show that increasing the number of control points can improve accuracy for heliostats with many facets, pixel precision has a significantly larger impact on camera calculation accuracy than facet canting and mounting errors, and the camera distance and focal length must be chosen to ensure adequate pixel accuracy on the heliostat surface depending on the size of heliostat. In conclusion, based on the results, recommendations for the allowable values of each parameter are provided to achieve the required NIO optical error estimation accuracy depending on the size of heliostat.

14 SOLAR ENERGY↗
NASA NTRS1982

KC-135 wing and winglet flight pressure distributions, loads, and wing deflection results with some wind tunnel comparisons

A full-scale winglet flight test on a KC-135 airplane with an upper winglet was conducted. Data were taken at Mach numbers from 0.70 to 0.82 at altitudes from 34,000 feet to 39,000 feet at stabilized flight conditions for wing/winglet configurations of basic wing tip, 15/-4 deg, 15/-2 deg, and 0/-4 deg winglet cant/incidence. An analysis of selected pressure distribution and data showed that with the basic wing tip, the flight and wind tunnel wing pressure distribution data showed good agreement. With winglets installed, the effects on the wing pressure distribution were mainly near the tip. Also, the flight and wind tunnel winglet pressure distributions had some significant differences primarily due to the oilcanning in flight. However, in general, the agreement was good. For the winglet cant and incidence configuration presented, the incidence had the largest effect on the winglet pressure distributions. The incremental flight wing deflection data showed that the semispan wind tunnel model did a reasonable job of simulating the aeroelastic effects at the wing tip. The flight loads data showed good agreement with predictions at the design point and also substantiated the predicted structural penalty (load increase) of the 15 deg cant/-2 deg incidence winglet configuration.

Montoya, L. C.↗
NASA NTRS1984

Interference effects of thrust reversing on horizontal tail effectiveness of twin-engine fighter aircraft at Mach numbers from 0.15 to 0.90

An investigation was conducted in the Langley 16 foot Transonic Tunnel to determine the interference effects of thrust reversing on horizontal tail effectiveness of a twin engine, general research fighter model at approach and in-flight speeds. Twin vertical tails at three longitudinal locations were tested at a cant angle of 0 deg. One configuration was also tested at a cant angle of 20 deg. Two nonaxisymmetric nozzle reverser concepts were studied. Test data were obtained at Mach numbers of 0.15, 0.60, and 0.90 and at angles of attack from -3 to 9 deg. Nozzle pressure ratios varied from jet off to 7.0, depending upon Mach number. At landing approach speed (Mach number 0.15), thrust reverser operation usually resulted in large variations (up to 70% increase) in horizontal tail effectiveness as nozzle pressure ratio was varied at zero angle of attack or as angle of attack was varied at constant nozzle pressure ratio. There was always a decrease in effectiveness at Mach numbers of 0.60 and 0.90 as a result of reverser operation.

Capone, F. J.↗
NASA NTRS1985

Effects of empennage surface location on aerodynamic characteristics of a twin-engine afterbody model with nonaxisymmetric nozzles

An investigation has been conducted in the Langley 16-Foot Transonic Tunnel to determine the effects of empennage surface location and vertical tail cant angle on the aft-end aerodynamic characteristics of a twin-engine fighter-type configuration. The configuration featured two-dimensional convergent-divergent nozzles and twin-vertical tails. The investigation was conducted with different empennage locations that included two horizontal and three vertical tail positions. Vertical tail cant angle was varied from -10 deg to 20 deg for one selected configuration. Tests were conducted at Mach number 0.60 to 1.20 and at angles of attack -3 to 9 deg. Nozzle pressure ratio was varied from jet off to approximately 9, depending upon Mach number. Tail interference effects were present throughout the range of Mach numbers tested and found to be either favorable or adverse, depending upon test condition and model configuration. At a Mach number of 0.90, adverse interference effects accounted for a significant percentage of total aft-end drag. Interference effects on the nozzle were generally favorable but became adverse as the horizontal tails were moved from a mid to an aft position. The configuration with nonaxisymmetric nozzles had lower total aft-end drag with tails-off than a similar configuration with axisymmetric nozzles at Mach numbers of 0.60 and 0.90.

Capone, Francis J.↗
NASA NTRS1992

High spatial resolution measurements in a single stage ram accelerator

High spatial resolution experimental tube wall pressure measurements of ram accelerator gas dynamic phenomena are presented in this paper. The ram accelerator is a ramjet-in-tube device which operates in a manner similar to that of a conventional ramjet. The projectile resembles the centerbody of a ramjet and travels supersonically through a tube filled with a combustible gaseous mixture, with the tube acting as the outer cowling. Pressure data are recorded as the projectile passes by sensors mounted in the tube wall at various locations along the tube. Utilization of special highly instrumented sections of tube has allowed the recording of gas dynamic phenomena with high resolution. High spatial resolution tube wall pressure data from the three regimes of propulsion studied to date (subdetonative, transdetonative, and superdetonative) in a single stage gas mixture are presented and reveal the three-dimensional character of the flow field induced by projectile fins and the canting of the fins and the canting of the projectile body relative to the tube wall. Also presented for comparison to the experimental data are calculations made with an inviscid, three-dimensional CFD code. The knowledge gained from these experiments and simulations is useful in understanding the underlying nature of ram accelerator propulsive regimes, as well as assisting in the validation of three-dimensional CFD coded which model unsteady, chemically reactive flows.

Hinkey, J. B.↗
NASA NTRS1958

Theoretical Calculations of Supersonic Wave Drag at Zero Lift for a Particular Store Arrangement

An analysis, based on the linearized thin-airfoil theory for supersonic speeds, of the wave drag at zero lift has been carried out for a simple two-body arrangement consisting of two wedgelike surfaces, each with a rhombic lateral cross section and emanating from a common apex. Such an arrangement could be used as two stores, either embedded within or mounted below a wing, or as auxiliary bodies wherein the upper halves could be used as stores and the lower halves for bomb or missile purposes. The complete range of supersonic Mach numbers has been considered and it was found that by orienting the axes of the bodies relative to each other a given volume may be redistributed in a manner which enables the wave drag to be reduced within the lower supersonic speed range (where the leading edge is substantially subsonic). At the higher Mach numbers, the wave drag is always increased. If, in addition to a constant volume, a given maximum thickness-chord ratio is imposed, then canting the two surfaces results in higher wave drag at all Mach numbers. For purposes of comparison, analogous drag calculations for the case of two parallel winglike bodies with the same cross-sectional shapes as the canted configuration have been included. Consideration is also given to the favorable (dragwise) interference pressures acting on the blunt bases of both arrangements.

Margolis, Kenneth↗
NASA NTRS2000

Laboratory and Field Measurements of Raindrop Oscillations

This study presents new measurements of raindrop oscillations in laboratory and field conditions. A 2-D video disdrometer is used to detect the shape of oscillating raindrops. The studies that were conducted to examine the oscillatory behavior of drops reveal that there is a lack of observations of the large drop oscillations. Yet, these drops have significant importance on radar rain estimation. Therefore, the new laboratory study is particularly designed to expand our knowledge on oscillatory behavior of large raindrops. The preliminary laboratory tests indicate that the drops are less oblate than the equilibrium shapes. Regarding the field studies, a large sample of raindrops was collected in several tropical field campaigns. The raindrops are mostly distorted and canted due to the environmental wind. An algorithm that determines the drop orientation and canting angle is added to the current system. This would reveal one of the most comprehensive data set on the oscillating behavior of raindrops in natural rain. The role of the oscillating raindrops on polarimetric parameters and subsequent rain estimation will be added to the discussion.

Tokay, A.↗