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Results for “Molecular Magnetism”

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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Fueling active galactic nuclei by magnetic braking

Recent detections of massive concentrations of molecular gas near the centers of galaxies hosting active nuclei suggest that these concentrations may be the source of accretion fuel for the nucleus. However, for that to be true, an angular momentum barrier must be overcome before the material in such a cloud can reach the nucleus. It is suggested that magnetic braking of the cloud may remove sufficient angular momentum to permit its material to draw considerably closer to the central object. The mechanism is particularly effective in the limit that the gas becomes self-gravitating because removal of a fraction of the initial angular momentum can lead to dynamical instability and collapse. Any small misalignment between the initial rotation axis of the cloud and the rotation axis of the galaxy can be substantially amplified as a result of the braking. It is argued that mass accretion onto the central object may occur in episodes, in some cases with a constant mass accretion rate during each episode.

Krolik, Julian H.↗
DOE OSTI2025

Mapping structures and dynamics with frequency-correlated diffusion exchange

Understanding molecular motion in diffusion-driven complex environments is critical for designing sustainable materials and improving chemical processes. Here, we introduce a multidimensional nuclear magnetic resonance (NMR) method that captures how molecular populations exchange across different dynamic regimes. By extending the modulated gradient spin-echo technique to include frequency-frequency correlations, our approach reveals diffusion pathways that are otherwise obscured in heterogeneous systems. Implemented on a unilateral NMR magnet, the method eliminates gradient pulsing constraints and accesses dynamics in the kilohertz regime. We apply this technique to swelling and acid-catalyzed deconstruction of cross-linked and linear polymers to observe how structural heterogeneity evolves over time. By linking molecular motion to topology and chemical state, we extract physical metrics such as fractal surface dimensionality and reaction wavefront velocity, properties inaccessible with standard diffusion measurements. This work expands the capabilities of NMR for probing soft matter, with implications for polymer recycling and materials design.

Fricke, Sophia N. [University of California, Berke↗
DOE OSTI2020

Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy

Large single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L 2,3 -edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine Fe I dopant ions to be linearly coordinated, occupying a D 6h symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe–N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner–Teller vibronic coupling and pseudo Jahn–Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L 2,3 -edge XAS from which the energy reduction of 3d z 2 due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L 3 -edge XAS can be applied to quantify the J = 7/2 magnetic anisotropy barrier, 34.80 meV (~280 cm –1 ), that corresponds with Orbach relaxation via the first excited, M J = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Dynamics of fluorinated imide-based ionic liquids using nuclear magnetic resonance techniques

There is increasing interest in studying molecular motions in ionic liquids to gain better insights into their transport properties and to expand their applications. Here, in this study, we have employed the fast field cycling relaxometry and pulsed field gradient nuclear magnetic resonance techniques to investigate the rotational and translational dynamics of fluorinated imide-based ionic liquids (ILs) at different temperatures. We have studied a total of six ILs composed of the 1-butyl-3-methylimidazolium cation ([BMIM] + ) combined with chemically modified analogs of the bis((trifluoromethyl)sulfonyl)imide anion ([NTf 2 ] − or [TFSI] − ). The primary objective of this paper is to broaden the understanding of how the anion's conformational flexibility, fluorination, and mass affect the molecular dynamics of cations and anions. Our results indicate that flexibility has the most significant impact on the rotational and translational motions of ions. Meanwhile, the effect of fluorination and mass is only relevant when conformational flexibility does not change significantly between the ILs being compared.

25 ENERGY STORAGE↗
DOE OSTI2023

Positional ordering induced by dynamic steric interactions in superparamagnetic rods

The dynamic motion produced by precessing magnetic fields can drive matter into far-from-equilibrium states. We predict 1D periodic ordering in systems of precessing rods when magnetic interactions between rods remain insignificant. The precession angle of the rods is completely determined by the field's precession angle and the ratio of the field's precession frequency and the characteristic response frequency of the rods. Here, we develop a molecular dynamics model that explicitly calculates magnetic interactions between particles, and we also simulate rods in the limit of a strong and fast precessing magnetic field where inter-rod magnetic interactions are negligible, using a purely steric model. Our simulations show how steric interactions drive the rods from a positionally disordered phase (nematic) to a layered (smectic) phase. As the rod precession angle increases, the nematic–smectic transition density significantly decreases. The minimization of unfavorable steric interactions also induces phase separation in binary mixtures of rods of different lengths. This effect is general to any force that produces precession in elongated particles. This work will advance the understanding and control of out-of-equilibrium soft matter systems.

42 ENGINEERING↗
NASA NTRS2005

A Deep X-ray Survey of Low-Mass PMS Stars in NGC 2264

Two X-ray images were obtained with the XMM-Newton spacecraft of more than 300 members of the NGC 2264 Open Cluster and its associated molecular cloud in order to investigate their magnetic activity. The X-ray fluxes extracted from those observations were used to study the dependence of stellar dynamo activity upon age and rotation for the optically revealed T Tauri stars and to place empirical constraints on theoretical models of angular momentum/dynamo evolution. The observations were also used to study the role of magnetic fields in the formation of low mass stars through the observation of very young protostars that are deeply embedded in the molecular cloud located behind the visible open cluster.

Simon, Theodore↗
DOE OSTI2022

On the use of stereodynamical effects to control cold chemical reactions: The H + D 2 ↔ D + HD case study

Here, quantum calculations are reported for the stereodynamic control of the H + D 2 ↔ D + HD chemical reaction in the energy range of 1–50 K. Stereodynamic control is achieved by a formalism similar to that reported by Perreault et al. [Nat. Chem. 10, 561 (2018)] in recent experimental works in which the alignment of the molecular bond axis relative to the incident relative velocity is controlled by selective preparations of the molecule in a specific or superposition of magnetic projection quantum numbers of the initial molecular rotational level. The approach presented here generalizes the experimental scheme of Perreault et al. and offers additional degree of control through various experimental preparations of the molecular alignment angle. Illustrative results presented for the H + D 2 and D + HD reactions show significant control with the possibility of turning the reaction completely on or off with the appropriate stereodynamic preparation of the molecular state. Various scenarios for maximizing and minimizing the reaction outcomes are identified with the selective preparation of molecular rotational states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

A Chemist’s Guide to Solid-State Qubits: Diamond Color Centers as Embedded Vacancy-Centered Molecules

Diamond point defects or color centers are at the crux of solid-state quantum technology applications, from computing to sensing. Modeling molecular qubits has advanced by leaps and bounds mainly due to the advanced quantum mechanical (QM) tools in the arsenal of quantum chemists for modeling (isolated) molecular systems, which should be easily translatable for analogous systems in the solid state. Here, we simulate a series of diamond defects: a carbon vacancy (V C ) and second row substitutions that are adjacent to a V C or D C V C , with D = B, N, and O, to evaluate their magnetic and optical properties. We applied molecular orbital principles, an embedded cluster method, and a multiconfigurational QM theory to computationally characterize the above-mentioned defects for a multitude of spin, charge, and excited states. Our computational approach delivered high-quality QM insights that compare well with experiments. Furthermore, with this framework, we confirm the spin-triplets B C V C – and O C V C 0 to be analogous to N C V C – , with calculated bright transitions that respectively correspond to UV (3.80 eV) and blue (2.65 eV) light absorption and emission lifetimes (τ) of 2.3 and 5.6 ns, which are higher in energy and more short-lived (and thus brighter) than that for N C V C – : green (2.26 eV), τ = 9.5 ns.

Martirez, John Mark P. [Princeton Plasma Physics L↗
NASA NTRS1993

Magnetic Field Structure in Monoceros R2

For some time now it has been suspected that magnetic fields play a major role in determining the mass spectrum of stars formed in molecular clouds. Theoretical models of protostellar evolution in a quiescent environment invoke magnetic fields as one form of cloud support and one which has a decisive effect on the minimum stellar mass formed (cf. Shu, Adams and Lizano 1987; Shu et al. 1988). The magnetic field also might act as an angular momentum dampening mechanism---a vital requirement for gravitational collapse and subsequent star formation (Gillis, Mestel and Paris 1974; Mouschovias 1978). Empirical evidence of the contribution of magnetic fields to the total energetics of molecular clouds comes from analysis of Zeeman splitting of OH absorption and thermal emission lines originating from dense (n greater than 10^4 cm^(-3)) cloud cores (Myers and Goodman 1988; Heiles et al. 1991, and references therein)...

Goldsmith, P.F.↗
DOE OSTI2025

Magnetic Ni-N-Ni Centers in N-substituted NiO

Here, to explore how anion substitution modifies the existing magnetism in strongly correlated oxides, we investigate local electronic states and magnetic ordering in nickel oxide (NiO) induced by substituting oxygen (O) with nitrogen (N). Each N introduces an additional N 2p hole and modifies the magnetic moment of a neighboring nickel (Ni) cation site, as the exchange interaction between this hole and the Ni $e_{g}$ electrons exceeds the Ni-O-Ni superexchange interaction. This leads to the formation of Ni-N-Ni centers consisting of five spins, without perturbing the antiferromagnetic NiO lattice. These centers are studied using density functional theory and confirmed through high-resolution spectroscopy on N-substituted NiO thin films grown by molecular beam epitaxy. This type of magnetic design may enable future advances in quantum technologies based on strongly correlated materials, such as quantum sensors and spin-based qubits.

Godin, Simon [Univ. of British Columbia, Vancouver↗
DOE OSTI2021

Synthesis, Magnetic Properties, and Electronic Structure of Magnetic Topological Insulator MnBi 2 Se 4

The intrinsic magnetic topological insulators MnBi 2 Te 4 and MnBi 2 Se 4 support novel topological states related to symmetry breaking by magnetic order. Unlike MnBi 2 Te 4 , the study of MnBi 2 Se 4 has been inhibited by the lack of bulk crystals, as the van der Waals (vdW) crystal is not the thermodynamic equilibrium phase. In this study, we report the layer-by-layer synthesis of vdW MnBi 2 Se 4 crystals using nonequilibrium molecular beam epitaxy. Atomic-resolution scanning transmission electron microscopy and scanning tunneling microscopy identify a well-ordered vdW crystal with septuple-layer base units. The magnetic properties agree with the predicted layered antiferromagnetic ordering but disagree with its predicted out-of-plane orientation. Instead, our samples exhibit an easy-plane anisotropy, which is explained by including dipole–dipole interactions. Angle-resolved photoemission spectroscopy reveals the gapless Dirac-like surface state, which demonstrates that MnBi 2 Se 4 is a topological insulator above the magnetic-ordering temperature. These studies show that MnBi 2 Se 4 is a promising candidate for exploring rich topological phases of layered antiferromagnetic topological insulators.

36 MATERIALS SCIENCE↗
NASA NTRS1988

The evolution of molecular clouds

The problem of the structure and evolution of molecular clouds is reviewed, with particular emphasis given to the relationship with star formation. The basic hypothesis is that magnetic fields are the primary agents for supporting molecular clouds, although damped Alfven waves may play an important role in the direction parallel to the field lines. This picture naturally leads to a conception of 'bimodal star formation'. It is proposed that high-mass stars form from the overall gravitational collapse of a supercritical cloud, whereas low-mass stars form from small individual cores that slowly condense by ambipolar diffusion from a more extended envelope until they pass the brink of graviational instability and begin to collapse dynamically from 'inside-out'. The evidence that the infall stage of protostellar evolution is terminated by the development of a powerful stellar wind is reviewed.

Shu, Frank H.↗
DOE OSTI2025

Experimental determination of the magnetic anisotropy in five-coordinated Co( II ) field-induced single molecule magnets

Magnetic anisotropy of the central metal atom is a crucial property of single molecule magnets (SMMs). Small structural changes can alter the magnetic properties, and accurate experimental methods to investigate magnetic anisotropy are therefore critical. Here, we investigate two five-coordinated Co( II ) SMMs, [CoCl 2 Cltpy] (1) and [CoBr 2 Cltpy] (2) (Cltpy = 4′-chloro-2,2′:6′,2′′-terpyridine), through multiple techniques. Ab initio theoretical calculations performed on the two compounds show that both possess axial magnetic anisotropy with the magnetic easy axis pointing towards one of the terminal halogen atoms. Theoretical calculations on SMMs are typically done on isolated molecular species, and to validate this approximation the magnetic anisotropy was further studied through experimental techniques. EPR measurements confirm an axial anisotropy of 1, and magnetic measurements provide experimental Zero-Field Splitting (ZFS) parameters, showing that the values from theoretical calculations are slightly overestimated. The X-ray electron density determined from 20 K single-crystal synchrotron X-ray diffraction data provides estimated d-orbital populations also suggesting axial magnetic anisotropy in both systems, and furthermore suggesting a more pronounced axiality in 1 compared to 2. This is in good agreement with the results obtained from both magnetic measurements and theoretical calculations. The magnetic anisotropy of 1 is quantified experimentally through polarized powder neutron diffraction via the site susceptibility method, confirming an axial magnetic anisotropy of the compound. A slight deviation in the easy axis direction is observed between experimental and theoretical results. This, together with the overestimation of the ZFS parameters from theoretical calculations, shows that experimental investigation of the magnetic anisotropy of SMMs is of high relevance. Magnetic anisotropy of the central metal atom is a crucial property of single molecule magnets (SMMs).

Slavensky, Hannah H. [Aarhus Univ. (Denmark)] (ORC↗
DOE OSTI2023

Probing Molecular Packing of Amorphous Pharmaceutical Solids Using X-ray Atomic Pair Distribution Function and Solid-State NMR

The structural investigation of amorphous pharmaceuticals is of paramount importance in comprehending their physicochemical stability. However, it has remained a relatively underexplored realm primarily due to the limited availability of high-resolution analytical tools. Here in this study, we utilized the combined power of X-ray pair distribution functions (PDFs) and solid-state nuclear magnetic resonance (ssNMR) techniques to probe the molecular packing of amorphous posaconazole and its amorphous solid dispersion at the molecular level. Leveraging synchrotron X-ray PDF data and employing the empirical potential structure refinement (EPSR) methodology, we unraveled the existence of a rigid conformation and discerned short-range intermolecular C–F contacts within amorphous posaconazole. Encouragingly, our ssNMR 19 F– 13 C distance measurements offered corroborative evidence supporting these findings. Furthermore, employing principal component analysis on the X-ray PDF and ssNMR data sets enabled us to gain invaluable insights into the chemical nature of the intermolecular interactions governing the drug–polymer interplay. These outcomes not only furnish crucial structural insights facilitating the comprehension of the underlying mechanisms governing the physicochemical stability but also underscore the efficacy of synergistically harnessing X-ray PDF and ssNMR techniques, complemented by robust modeling strategies, to achieve a high-resolution exploration of amorphous structures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1997

HIRES Dust Imaging of the NGC 6334 Star Forming Complex

We present here our final report for the NASA grant "HIRES Dust Imaging of the NGC 6334 Star Forming Complex." This project was designed to study the photodissociation regions surrounding several OB stars in this cloud complex. NGC 6334 is unique in having at least seven distinct massive star forming regions in the same molecular cloud complex. The obvious advantage of studying young stars in the same molecular complex is that the stars all formed in the same global environment. Consequently, global factors like density waves, abundances, global magnetic field strength, and age of the parental molecular cloud cannot contribute to the differences among the star forming regions. Instead, the differences must arise only from local effects such as the mass, age, and UV fields of the individual stars. A study of NGC 6334 will greatly simplify the general problem of comparing different star formation regions by eliminating global effects.

Jackson, James M.↗
DOE OSTI2021

Exchange-biased quantum tunnelling of magnetization in a [Mn 3 ] 2 dimer of single-molecule magnets with rare ferromagnetic inter-Mn 3 coupling

A covalently-linked dimer of two single-molecule magnets (SMMs), [Mn 6 O(O 2 CMe) 6 (1,3-ppmd) 3 ](ClO 4 ) 2 , has been synthesized from the reaction of [Mn 3 O(O 2 CMe) 6 (py) 3 ](ClO 4 ) with 1,3-phenylene-bis(pyridin-2-ylmethanone) dioxime (1,3-ppmdH 2 ). It contains two [Mn III 3 O] +7 triangular units linked by three 1,3-ppmd 2 - groups into an [Mn 3 ] 2 dimer with D 3 symmetry. Solid-state dc and ac magnetic susceptibility measurements showed that each Mn 3 subunit retains its properties as an SMM with an S = 6 ground state. Magnetization vs. dc field sweeps on a single crystal reveal hysteresis loops below 1.3 K exhibiting exchange-biased quantum tunnelling of magnetization (QTM) steps with a bias field of +0.06 T. This is the first example of a dimer of SMMs showing a positive exchange bias of the QTM steps in the hysteresis loops, and it has therefore been subjected to a detailed analysis. Simulation of the loops determines that each Mn3 unit is exchange-coupled with its neighbour primarily through the 1,3-ppmd 2 - linkers, confirming a weak ferromagnetic inter-Mn 3 interaction of J 12 ≈ +6.5 mK ($\hat{H}= -2J\hat{S}_i·\hat{S}_j$ convention). High-frequency EPR studies of a microcrystalline powder sample enable accurate determination of the zero-field splitting parameters of the uncoupled Mn3 SMMs, while also confirming the weak exchange interaction between the two SMMs within each [Mn 3 ] 2 dimer. The combined results emphasize the ability of designed covalent linkers to generate inter-SMM coupling of a particular sign and relative magnitude, and thus the ability of such linkers to modulate the quantum physics. As such, this article supports the feasibility of using designed covalent linkers to develop molecular oligomers of SMMs, or other magnetic molecules, as multi-qubit systems and/or other components of new quantum technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

From sequence to protein structure and conformational dynamics with artificial intelligence/machine learning

The 2024 Nobel Prize in Chemistry was awarded in part for de novo protein structure prediction using AlphaFold2, an artificial intelligence/machine learning (AI/ML) model trained on vast amounts of sequence and three-dimensional structure data. AlphaFold2 and related models, including RoseTTAFold and ESMFold, employ specialized neural network architectures driven by attention mechanisms to infer relationships between sequence and structure. At a fundamental level, these AI/ML models operate on the long-standing hypothesis that the structure of a protein is determined by its amino acid sequence. More recently, AlphaFold2 has been adapted for the prediction of multiple protein conformations by subsampling multiple sequence alignments. Herein, we provide an overview of the deterministic relationship between sequence and structure, which was hypothesized over half a century ago with profound implications for the biological sciences ever since. We postulate that protein conformational dynamics are also determined, at least in part, by amino acid sequence and that this relationship may be leveraged for construction of AI/ML models dedicated to predicting protein conformational ensembles. Accordingly, we describe a conceptual model architecture, which may be trained on sequence data in combination with conformationally sensitive structural information, coming primarily from nuclear magnetic resonance (NMR) spectroscopy. Notwithstanding certain limitations in this context, NMR offers abundant structural heterogeneity conducive to conformational ensemble prediction. As NMR and other data continue to accumulate, sequence-informed prediction of protein structural dynamics with AI/ML has the potential to emerge as a transformative capability across the biological sciences.

Artificial intelligence↗
DOE OSTI2023

Transport Properties of Magnetized High-Energy Density Plasma (Final Project Report)

This report summarizes results of project DE-SC0016159 "Transport Properties of Magnetized High-Energy-Density Plasma,'' which ran from 7/15/2016 - 7/14/2021. The primary objectives of the work, as stated in the original proposal, were to develop a theory that describes transport coefficients in magnetized high energy density plasmas and to test the theory with molecular dynamics (MD) simulations. The science challenge is that strong ion coupling, strong magnetization of electrons, and partial degeneracy of electrons, cause the system to be in a regime that is not well described by current theory. The particular processes that were to be investigated include: ion stopping power, diffusion, electron-ion temperature relaxation, thermal conduction and viscosity. All of the primary research objectives were accomplished during the course of this work. In addition, some unexpected results were discovered along the way that led to new and productive research directions. This work resulted in 17 publications in well-respected peer-reviewed journals (primarily Physics of Plasmas and Physical Review E), and 2 more are being prepared for publication. A few of these were selected as Editor's Picks and one was published as a Rapid Communication. Highlights of the research results include: Transport phase space: The first identification of the parameter space that defines fundamental transport regimes in terms of the Coulomb coupling and magnetization parameters. Mean force kinetic theory: Systematic derivation of a kinetic theory for strongly coupled plasmas based on a new expansion parameter of the BBGKY hierarchy. This provided the derivation of a theory that we had previously posed phenomenologically, and also revealed a new term that captures the equation of state properties at all coupling strengths. Transverse friction force: Discovery that the friction force on a test charge in a strongly magnetized plasma includes a component that is perpendicular to the motion of the test charge in the plane defined by the velocity and magnetic field vectors. Gyrofriction force: Discovery that the friction force on a test charge in a plasma that is both strongly magnetized and strongly coupled includes a component of the force in the direction of the Lorentz force. Kinetic theory for warm dense matter: Extension of the mean force kinetic theory to include partial electron degeneracy, so that it applies to warm dense matter.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗