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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 OSTI2022

Electronic structure of the frustrated diamond lattice magnet NiRh 2 O 4

We report the A -site spinel NiRh 2 O 4 is the only known realization of a spin-1 diamond lattice magnet and is predicted to host unconventional magnetic phenomena driven by frustrated nearest and next-nearest neighbor exchange as well as orbital degeneracy. Previous works found no sign of magnetic order but found a gapped dispersive magnetic excitation indicating a possible valence bond magnetic ground state. However, the presence of many competing low energy degrees of freedom and limited empirical microscopic constraints complicates further analysis. Here we carry out resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy (XAS), and inelastic neutron scattering (INS) to characterize the local electronic structure and lattice dynamics of NiRh 2 O 4 . The RIXS data can be partly described by a single-ion model for tetrahedrally coordinated Ni 2+ and indicates a tetragonal distortion Δt 2 = 70 meV that splits the t 2 orbitals into a high energy orbital singlet and lower energy orbital doublet. We identify features of the RIXS spectra that are consistent with a Rh-Ni two-site excitation indicating strong metal-metal hybridization mediated by oxygen in NiRh 2 O 4 . We also identify signatures of electron-phonon coupling through the appearance of phonon sidebands that dress crystal field excitations. These results establish the key energy scales relevant to the magnetism in NiRh 2 O 4 and further demonstrate that covalency and lattice dynamics play essential roles in controlling the magnetic ground states of A -site spinels.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Unraveling the Orbital Physics in a Canonical Orbital System KCuF 3

We explore the existence of the collective orbital excitations, orbitons, in the canonical orbital system KCuF 3 using the Cu L 3 -edge resonant inelastic x-ray scattering. We show that the nondispersive high-energy peaks result from the Cu 2+ dd orbital excitations. These high-energy modes display good agreement with the ab initio quantum chemistry calculation, indicating that the d d excitations are highly localized. At the same time, the low-energy excitations present clear dispersion. They match extremely well with the two-spinon continuum following the comparison with Müller ansatz calculations. The localized d d excitations and the observation of the strongly dispersive magnetic excitations suggest that the orbiton dispersion is below the resolution detection limit. Our results can reconcile with the strong local Jahn-Teller effect in KCuF 3 , which predominantly drives orbital ordering.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Chemical heterogeneity modulated zero thermal expansion alloy over super-wide temperature range

Chemical heterogeneity is usually avoided in solution chemistry, but it may still occur with sometimes dramatic effects on target materials and their properties. Here, we propose chemical heterogeneity as a counterintuitive strategy to design high-performance zero thermal expansion (ZTE) alloys. We apply this approach in a Hf-Ti-Fe alloy with excess Fe in the Hf/Ti sublattice and produce Hf/Ti concentration alternations at the micro level. Such chemical heterogeneity regulates local magnetic interactions in alloy and triggers a dispersed magnetic phase transition that modulates the thermal expansions at the micro level and hence results in a remarkable ZTE behavior over a super-wide temperature window from 10 to 480 K. This mechanism is supported by comprehensive studies on morphological microstructures, crystal and magnetic structures, and theoretical calculations. The strategy of local chemical heterogeneity opens up an avenue to design ZTE and the related functional materials directly via microstructure engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2016

STATISTICALLY DETERMINED DISPERSION RELATIONS OF MAGNETIC FIELD FLUCTUATIONS IN THE TERRESTRIAL FORESHOCK

We obtain dispersion relations of magnetic field fluctuations for two crossings of the terrestrial foreshock by Cluster spacecraft. These crossings cover plasma conditions that differ significantly in their plasma β and in the density of the reflected ion beam, but not in the properties of the encountered ion population, both showing shell-like distribution function. Dispersion relations are reconstructed using two-point instantaneous wave number estimations from pairs of Cluster spacecraft. The accessible range of wave vectors, limited by the available spacecraft separations, extends to ≈2 × 10{sup 4} km. Results show multiple branches of dispersion relations, associated with different powers of magnetic field fluctuations. We find that sunward propagating fast magnetosonic waves and beam resonant modes are dominant for the high plasma β interval with a dense beam, while the dispersions of the interval with low beam density include Alfvén and fast magnetosonic modes propagating sunward and anti-sunward.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Effect of Heat Treatment on the Dispersion of the Magnetic Anisotropy of MnSb Nanoinclusions Embedded in Thin GaMnSb Films

We observed a temperature-controlled increase in the magnetic anisotropy and its dispersion in thin GaMnSb films with MnSb nanoinclusions obtained by pulsed laser deposition. The data of transmission electron microscopy indicate that in the samples, a transition of the crystalline structure of magnetic MnSb nanoinclusions from hexagonal (spatial group (sp. gr.) P6{sub 3}/mmc) to cubic (sp. gr. F-43m) takes place. Analysis of the temperature dependences of the magnetic moment m(T), measured using a SQUID magnetometer, obtained for both unannealed and annealed samples cooled in a zero magnetic field and a magnetic field of 10 kOe, indicates that this mechanism is not unique. In unannealed samples, the distribution of the magnetic anisotropy of MnSb nanoinclusions, determined from the dependences of m(T), is unimodal. In the annealed samples, the same dependence becomes multimodal. This means that several thermally activated processes occur in the samples during annealing, resulting in several “populations” of nanoinclusions present in the annealed thin films. The contribution to the increase in the magnetic anisotropy during annealing can result in the structural phase transition, the mismatch of the crystal lattices between MnSb and GaSb, an increase in the average volume of MnSb nanoinclusions, and a change in their stoichiometry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1971

Annealing effects in plated-wire memory elements. II - Recrystallization in Permalloy films.

Results of grain-size measurements in Permalloy platings suggest that recrystallization is possible at temperatures as low as 200 C, but that it is an extremely heterogeneous process. No worthwhile correlation was found to exist between observed grain size and magnetic dispersion in samples aged in the temperature range from 180 to 230 C. It is suggested that the magnetic aging which occurs under these conditions may be due to some other diffusion-controlled process than recrystallization; a process such as chemical homogenization is tentatively preferred.

Marquardt, S. J.↗
DOE OSTI2011

Controllable Raman soliton self-frequency shift in nonlinear metamaterials

Controllable and dispersive magnetic permeability in the metamaterials (MMs) provides us more freedom to harness the propagation of ultrashort electromagnetic pulses at will. Here we discuss the controllability of the Raman soliton self-frequency shift (SSFS) in the MMs with a nonlinear electric polarization. First, we derive a generalized nonlinear Schroedinger equation suitable for few-cycle pulse propagation in the MMs with delayed Raman response, and demonstrate the Raman effect, high-order Raman-related nonlinearity, and high-order nonlinear dispersion terms occurring in this equation. Second, we present a theoretical investigation on the controllability of the Raman SSFS in the MMs. In particular, we identify the combined effects of the anomalous self-steepening (SS), third-order dispersion (TOD), and Raman effect on SSFS. It is shown that the positive SS effect suppresses SSFS; however, the negative SS effect enhances SSFS, and the positive TOD leads to the deceleration of SSFS. Finally, the effects of SS on the SSFS of the second-order soliton are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Giant spin gap and magnon localization in the disordered Heisenberg antiferromagnet Sr 2 Ir 1 - x Ru x O 4

Here, we study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet Sr 2 Ir 1–x RuxO 4 . The maximum energy of the magnetic excitation remains robust up to x = 0.77, with a gap opening at low dopings and increasing to over 150 meV at x = 0.77. At these higher Ru concentrations, the dispersive magnetic excitations in Sr 2 IrO 4 are rendered essentially momentum independent. Up to a Ru concentration of x = 0.77, both experiments and first-principles calculations show the Ir J eff = 1/2 state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder. Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest-neighbor ferromagnetic coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

A stretch/compress scheme for a high temporal resolution detector for the magnetic recoil spectrometer time (MRSt)

Here we present a time-resolved detector concept for the magnetic recoil spectrometer for time-resolved measurements of the NIF neutron spectrum. The measurement is challenging due to the time spreading of the recoil protons (or deuterons) as they transit an energy dispersing magnet system. Ions arrive at the focal plane of the magnetic spectrometer over an interval of tens of nanoseconds. We seek to measure the time-resolved neutron spectrum with 20 ps precision by manipulating an electron signal derived from the ions. A stretch-compress scheme is employed to remove transit time skewing while simultaneously reducing the bandwidth requirements for signal recording. Simulation results are presented along with design concepts for structures capable of establishing the required electromagnetic fields.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Neutron scattering study of magnetic excitations in a 5d-based double-perovskite Ba2FeReO6

Motivated by exploring spin-orbit-coupled magnetism in 5d-based transition metal oxides (TMOs) beyond the iridates, we present a powder inelastic neutron scattering study of magnetic excitations in Ba2FeReO6 - a member of the double-perovskite family of materials which exhibit half-metallic behavior and high Curie temperatures Tc. We find clear evidence of two well-defined dispersing magnetic modes in its low-temperature ferromagnetic state. We develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re and show that it captures our experimental observations. This allows us to extract moment sizes and exchange couplings, explain the magnitude of Tc, and infer that magnetostructural locking terms are weak. Our study further opens up Re-based compounds as model systems to explore the interplay of strong correlations and spin-orbit coupling in 5d TMOs.

Plumb, K. W.↗
DOE OSTI2024

Magnetically oriented nanosheet interlayer for dynamic regeneration in lithium metal batteries

Lithium (Li) metal has been recognized as a promising anode to advance the energy density of current Li-based batteries. However, the growth of the solid–electrolyte interphase (SEI) layer and dendritic Li microstructure pose significant challenges for the long-term operation of Li metal batteries (LMBs). Herein, we propose the utilization of a suspension electrolyte with dispersed magnetically responsive nanosheets whose orientation can be manipulated by an external magnetic field during cell operation for realizing in situ regeneration in LMBs. The regeneration mechanism arises from the redistribution of the ion flux and the formation of an inorganic-rich SEI for uniform and compact Li deposition. With the magnetic-field-induced regeneration process, we show that a Li||Li symmetric cell stably operates for 350 h at 2 mA cm −2 and 2 mA h cm −2 , ~5 times that of the cell with the pristine electrolyte. Furthermore, the cycling stability can be significantly extended in the Li||NMC full cell of 3 mA h cm −2 , showing a capacity retention of 67% after 500 cycles at 1C. The dynamic Li metal regeneration demonstrated here could bring useful design considerations for reviving the operating cells for achieving high-energy, long-duration battery systems.

Ju, Zhengyu↗
DOE OSTI2025

Spin dynamics in the itinerant antiferromagnet SrCr 2 ⁢As 2

SrCr 2 ⁢As 2 is an itinerant antiferromagnet in the same structural family as the SrFe 2 ⁢As 2 high-temperature superconductors. Here, we report our calculations of exchange-coupling parameters 𝐽 𝑖⁢𝑗 for SrCr 2 ⁢As 2 using a static linear-response method based on first-principles electronic-structure calculations. We find that the dominant nearest-neighbor exchange coupling 𝐽 1 >0 is antiferromagnetic whereas the next-nearest-neighbor exchange coupling 𝐽 2 <0 is ferromagnetic with 𝐽 2 /𝐽 1 = −0.68, reinforcing the checkerboard in-plane magnetic structure. Thus, unlike other transition-metal arsenides based on Mn, Fe, or Co, we find no competing magnetic interactions in SrCr 2 ⁢As 2 , which aligns with experimental findings. Moreover, the orbital resolution of exchange interactions shows that 𝐽 1 and 𝐽 2 are dominated by direct exchange mediated by the Cr 𝑑 orbitals. To validate the calculations we conduct inelastic neutron-scattering measurements on powder samples that show steeply dispersive magnetic excitations arising from the magnetic Γ points and persisting up to energies of at least 175 meV. The spin-wave spectra are then modeled using the Heisenberg Hamiltonian with the theoretically calculated exchange couplings. In conclusion, the calculated neutron-scattering spectra are in good agreement with the experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

CoSyR: A novel beam dynamics code for the modeling of synchrotron radiation effects

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamics code is developed based on a Lagrangian method for the calculation of the particles’ radiation near-fields using wavefront/wavelet meshes via the Green’s function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in 2D/3D simulations at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. Here, the current 2D implementation of CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed. Extension of the core algorithms to 3D is possible and planned.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Design of flexible proton beam imaging energy spectrometers (PROBIES)

A simple repeating step-filtered structure has been designed and deployed for the detection of MeV-energy proton beams produced from high-intensity short-pulse laser-driven experiments. Due to the diagnostic's ability to recover energy-resolved images of proton beams, it is called the proton beam imager and energy spectrometer (or PROBIES). The flexible design has two useful applications. First, it can be fielded in a configuration with a scintillator and imaging setup in order to collect proton beam information in high-repetition rate experiments. Here we show a configuration that collects the equivalent of a nine-film radiochromic film (RCF) stack, and a technique for using a neural network (NN) to rapidly analyze the images on millisecond time-scales. Second, when using RCF stacks as the detector, the energy resolution capability is greatly increased compared to traditional RCF stacks, while simultaneously reducing the total number of films required to make each measurement. We demonstrate a configuration that provides up to 90 spatially- and energy-resolved datapoints using just ten films. Both designs presented here can be easily customized for anticipated experimental outputs and manufactured at low cost. Such designs allow for rapid prototyping using modern high-accuracy 3D printers or on-demand computer numerical control machining to reduce the reliance on time-consuming film media, analysis, or bulky electro-magnetically dispersing spectrometers. The analysis of data is discussed and a methodology for constructing a NN that is capable of rapidly analyzing data on-the-fly with greater than 95% accuracy is presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface

Adsorption behavior of Fe atoms on a metal-free naphthalocyanine (H 2 Nc) monolayer on Ag(111) surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory (DFT) based calculations. We found that the Fe atoms adsorbed at the centers of H 2 Nc molecules and formed Fe-H 2 Nc complexes at low coverage. DFT calculations show that the configuration of Fe at the center of a molecule is the most stable site, in good agreement with the experimental observations. After an Fe-H 2 Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe-H 2 Nc complex monolayer. Furthermore, the H 2 Nc monolayer grown on Ag(111) could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Strong anisotropy within a Heisenberg model in the J eff = 1 2 insulating state of Sr 2 Ir 0.8 Ru 0.2 O 4

The dispersive magnetic excitations in Sr 2 IrO 4 have previously been well described within an isospin-1/2 Heisenberg model on a square lattice that revealed parallels with La 2 CuO 4 . In this paper, we investigate the inelastic spectra of Sr 2 Ir 0.8 Ru 0.2 O 4 with resonant inelastic x-ray scattering (RIXS) at the Ir L 3 edge. The results are well described using linear spin-wave theory within a similar Heisenberg model applicable to Sr 2 IrO 4 ; however, the disorder induced by the substitution of 20% Ir 4+ ions for Ru 4+ removes longer range exchange interactions. A large spin gap (40 meV) is measured indicating strong anisotropy from spin-orbit coupling that is manifest due to the altered magnetic structure in Sr 2 Ir 0.8 Ru 0.2 O 4 with c-axis aligned moments compared to the basal plane moments in the parent. Finally, collectively the results indicate the robustness of a Heisenberg model description even when the magnetic structure is altered and the J eff = 1/2 moments are diluted.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗