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At least 235 records · Page 13

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DOE OSTI2023

On the effects of quadrupolar relaxation in Earth’s field NMR spectra

There is growing interest in using low-field magnetic resonance experiments for routine chemical characterization. Earth’s field NMR is one such technique that can garner structural information and enable sample differentiation with low cost and highly portable designs. The resulting NMR spectra are primarily influenced by $J$-couplings, resulting in so-called $J$-coupled spectra (JCS). Many small molecules include atoms with NMR-active nuclei that are quadrupolar either at natural abundance or are often isotopically enriched (e.g., 2 H, 6 Li, 11 B, 14 N, 17 O, etc.) where the effects of quadrupolar J-couplings and relaxation on JCS of strongly- and weakly-coupled spin systems have not been explored to date. Herein, using a set of seven fluoropyridine samples with unique substitution and $J$-couplings, we demonstrate that the 14 N relaxation rates can induce drastic line-broadening in the JCS. This includes a previously unexplored unique line broadening mechanism enabled by strongly coupled spins at low-field. In conclusion, numerical simulations are used to model and refine the magnitudes and signs of $J$-couplings, as well as indirectly determine the 14 N relaxation rates in a single 1D experiment that has a higher fidelity than observed in high-field NMR experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Paramagnetic Mn 8 Fe 4 -co-Polystyrene Nanobeads as a Potential T 1 –T 2 Multimodal Magnetic Resonance Imaging Contrast Agent with In Vivo Studies

In developing a cluster-nanocarrier design, as a magnetic resonance imaging contrast agent, we have investigated the enhanced relaxivity of a manganese and iron-oxo cluster grafted within a porous polystyrene nanobead with increased relaxivity due to a higher surface area. The synthesis of the cluster-nanocarrier for the cluster Mn 8 Fe 4 O 12 (O 2 CC 6 H 4 CH=CH 2 ) 16 (H 2 O) 4 , cross-linked with polystyrene (the nano-carrier), under miniemulsion conditions is described. By including a branched hydrophobe, iso-octane, the resulting nanobeads are porous and similar to 70 nm in diameter. The increased surface area of the nanobeads compared to nonporous nanobeads leads to an enhancement in relaxivity; r 1 increases from 3.8 to 5.2 ± 0.1 mM -1 s -1 , and r 2 increases from 11.9 to 50.1 ± 4.8 mM -1 s -1 , at 9.4 teslas, strengthening the potential for T 1 and T 2 imaging. Several metrics were used to assess stability, and the porosity produced no reduction in metal stability. Synchrotron X-ray fluorescence microscopy was used to demonstrate that the nanobeads remain intact in vivo . In depth, physicochemical characteristics were determined, including extensive pharmacokinetics, in vivo imaging, and systemic biodistribution analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

A mechanism for ageing in a deeply supercooled molecular glass

Measurements of the decay of electric fields, formed spontaneously within vapour-deposited films of cis-methyl formate, provide the first direct assessment of the energy barrier to secondary relaxation in a molecular glass. At temperatures far below the glass transition temperature, the mechanism of relaxation is shown to be through hindered molecular rotation. Magnetically-polarised neutron scattering experiments exclude diffusion, which is demonstrated to take place only close to the glass transition temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Approach to nonlinear magnetohydrodynamic simulations in stellarator geometry

The capability to model the nonlinear magnetohydrodynamic (MHD) evolution of stellarator plasmas is developed by extending the M3D-C 1 code to allow non-axisymmetric domain geometry. We introduce a set of logical coordinates, in which the computational domain is axisymmetric, to utilize the existing finite-element framework of M3D-C 1 . A C 1 coordinate mapping connects the logical domain to the non-axisymmetric physical domain, where we use the M3D-C 1 extended MHD models essentially without modifications. We present several numerical verifications on the implementation of this approach, including simulations of the heating, destabilization, and equilibration of a stellarator plasma with strongly anisotropic thermal conductivity, and of the relaxation of stellarator equilibria to integrable and non-integrable magnetic field configurations in realistic geometries.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2021

Dynamical ground state in the XY pyrochlore Yb2GaSbO7

Abstract The magnetic ground state of the pyrochlore Yb 2 GaSbO 7 has not been established. The persistent spin fluctuations observed by muon spin-relaxation measurements at low temperatures have not been adequately explained for this material using existing theories for quantum magnetism. Here we report on the synthesis and characterisation of Yb 2 GaSbO 7 to revisit the nature of the magnetic ground state. Through DC and AC magnetic susceptibility, heat capacity, and neutron scattering experiments, we observe evidence for a dynamical ground state that makes Yb 2 GaSbO 7 a promising candidate for disorder-induced spin-liquid or spin-singlet behaviour. This state is quite fragile, being tuned to a splayed ferromagnet in a modest magnetic field μ 0 H c ~ 1.5 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Spin–Lattice Relaxation Decoherence Suppression in Vanishing Orbital Angular Momentum Qubits

Multifrequency electron paramagnetic resonance spectroscopy on oriented single crystals of magnetically dilute Gd(III) ions in Gd 0.004 Y 0.996 (trensal) is used to determine the Hamiltonian parameters of the ground 8 S 7/2 term and its phase memory time, Tm, characterizing its coherent spin dynamics. Here, the vanishing orbital angular momentum of the 8 S 7/2 term makes it relatively insensitive to spin–lattice relaxation mediated by magnetoelastic coupling and leads to a T m of 12 μs at 3 K, which is not limited by spin–lattice relaxation.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Imitation of spin density wave order in Cu 3 Nb 2 O 8

Spin density waves, based on modulated local moments, are usually associated with metallic materials, but have recently been reported in insulators which display coupled magnetic and structural order parameters. Here, we discuss one such example, the multiferroic Cu 3 Nb 2 O 8 , which is reported to undergo two magnetic phase transitions, first to an unknown antiferromagnetic phase at $T_N$ ≈ 26.5 K , and then to a helicoidal structure coupled to an electric polarization below $T_2$ ≈ 24 K which breaks the crystallographic inversion symmetry. By analogy with other complex oxides, one might naturally expect this intermediate phase to be a spin density wave phase. We apply spherical polarimetry to confirm the low-temperature magnetic structure, yet only observe a single magnetic phase transition to helicoidal order. We argue that the reported unknown phase actually supports an imitation spin density wave which originates from a decoupling of the components of the magnetic order parameter, as allowed by symmetry and driven by thermal fluctuations. This provides a mechanism for the magnetic, but not nuclear, structure to break inversion symmetry thereby creating an intermediate phase in the proximity of $T_N$ which imitates a spin density wave. As the temperature is reduced, this intermediate structure destabilizes the crystal such that a structural chirality is induced, as reflected by the emergence of the electric polarization, and the imitation spin density wave relaxes into a generic helicoid. This scenario in which critical fluctuations allow the magnetic structure to break inversion symmetry while the crystal structure remains centrosymmetric might be relevant to other complex multiferroics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Controlling magnetism and transport at perovskite cobaltite interfaces via strain-tuned oxygen vacancy ordering

Complex oxides such as perovskite cobaltites exhibit rich phenomena at interfaces due to the complex interplay between their structural, defect, electronic, and magnetic degrees of freedom. Here, we study this interplay here in the ferromagnetic metallic cobaltite La 1−𝑥 ⁢Sr 𝑥⁢ CoO 3−𝛿 , using specific substrates to vary both the heteroepitaxial strain (compressive vs tensile) and growth orientation ((001) vs (110)). Transmission electron microscopy, electron energy-loss spectroscopy, high-resolution X-ray diffraction, magnetometry, polarized neutron reflectometry, and electronic magnetotransport measurements are applied. Lattice mismatch and growth orientation are found to enable the precise control of interfacial oxygen vacancy ordering in La 1−𝑥⁢ Sr 𝑥 ⁢CoO 3−𝛿 , thus dictating strain relaxation and oxygen vacancy depth profiles, in turn controlling thickness-dependent magnetic and electronic properties. In particular, compressive strain and (110) orientations minimize deleterious magnetic/electronic dead layer effects, leading to the optimization of interfacial magnetism and transport. Strain and orientation tuning of oxygen vacancy ordering are thus established as powerful means to control physical properties at cobaltite-based interfaces, relevant to several fields.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Above room temperature multiferroic and magnetoelectric properties of (1‐Φ) PZTFT‐Φ CZFMO particulate composites

Magnetoelectric (ME) composites of suitable ferroelectric and magnetic materials can display elevated magnetic and ferroelectric operational temperatures, along with substantial ME coupling, compared to conventional single-phase multiferroics. Herein, we describe the synthesis of (1-Φ) PZTFT-Φ CZFMO, Φ = 0.1, 0.2, 0.3 (PZTFT: [0.6(PbZr 0.53 Ti 0.47 O 3 )–0.4(PbFe 0.5 Ta 0.5 )O 3 ] CZFMO: Co 0.6 Zn 0.4 Fe 1.7 Mn 0.3 O 4 )] particulate (0–3) composites and report on the magnetic as well as ferroelectric phase transitions and magnetoelectric coupling. The phase formation and the induced strain in these composites are investigated via Raman spectroscopy. A large bifurcation of the zero-field cooled-field cooled magnetization curves confirms the highly anisotropic behavior of the composites. These curves also identify spin glass behavior in the CZFMO phase at ≈230 K. The magnetic phase transition of the composite (Φ = 0.2) is reported to be ≈532 (± 10) K. The temperature dependent dielectric data displays the ferroelectric phase transitions from the PZTFT phase and the broad relaxation peak from the CZFMO phase. The quadratic relationship between the magneto-capacitance and the magnetization confirms the existence of biquadratic magnetoelectric coupling in the systems. The collective results are consistent with the presence of a direct magneto-electric effect in the composites, i.e., by the application of magnetic field, the magnetic phase is strained, and this induced strain is responsible for changes of ferroelectric order parameter in the piezoelectric phase. As a result, this attribute makes the current composite structure a promising candidate for multiferroic data storage and processing technologies.

Bhoi, Krishnamayee↗

DOE OSTI2025

Dynamic signatures of spin-lattice coupling in the layered ferrimagnet Mn 3 Si 2 Te 6

Magnetic van der Waals (vdW) materials exhibit a profound interconnectedness between their various degrees of freedom, pointing to a wealth of potential applications in low-power and high-speed spintronic devices. Recently, light-matter interactions have been leveraged as robust, dynamic pathways to gain control over the properties of vdW magnets through the use of ultrafast pulses of light. Here, we utilize ultrafast photoexcitation to drive coherent lattice oscillations in the layered ferrimagnetic crystal Mn 3 Si 2 Te 6 , which significantly stiffen below the magnetic ordering temperature. We suggest that this is due to an exchange-mediated contraction of the lattice, stemming from strong magneto-structural coupling in this material. Furthermore, simulations of the transient incoherent response uncover the critical role of the spin-mediated electronic relaxation pathways. These results underscore the importance of spin-lattice coupling in vdW magnets and demonstrate a promising strategy for their dynamic optical control via their entangled degrees of freedom.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Revision of Faraday rotation measure constraints on the primordial magnetic field using the IllustrisTNG simulation

ABSTRACT Previously derived Faraday rotation constraints on the volume-filling intergalactic magnetic field (IGMF) have used analytical models that made a range of simplifying assumptions about magnetic field evolution in the intergalactic medium and did not consider the effect of baryonic feedback on large-scale structures. In this work, we revise existing Faraday rotation constraints on the IGMF using a numerical model of the intergalactic medium from the IllustrisTNG cosmological simulation that includes a sophisticated model of the baryonic feedback. We use the IllustrisTNG model to calculate the rotation measure and compare the resulting mean and median of the absolute value of the rotation measure with data from the NRAO VLA Sky Survey (NVSS). The numerical model of the intergalactic medium includes a full magnetohydrodynamic model of the compressed primordial magnetic field as well as a model of the regions where the magnetic field is not primordial, but is rather produced by the process of baryonic feedback. Separating these two types of regions, we are able to assess the influence of the primordial magnetic field on the Faraday rotation signal. We find that by correcting for regions of compressed primordial field and accounting for the fact that part of the intergalactic medium is occupied by magnetic fields spread by baryonic feedback processes rather than by the primordial field relaxes the Faraday rotation bound by a factor of ≃3. This results in B0 < 1.8 × 10−9 G for large correlation length IGMFs.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

High-sensitivity in vivo contrast for ultra-low field magnetic resonance imaging using superparamagnetic iron oxide nanoparticles

Magnetic resonance imaging (MRI) scanners operating at ultra-low magnetic fields (ULF; <10 mT) are uniquely positioned to reduce the cost and expand the clinical accessibility of MRI. A fundamental challenge for ULF MRI is obtaining high-contrast images without compromising acquisition sensitivity to the point that scan times become clinically unacceptable. Here, we demonstrate that the high magnetization of superparamagnetic iron oxide nanoparticles (SPIONs) at ULF makes possible relaxivity- and susceptibility-based effects unachievable with conventional contrast agents (CAs). We leverage these effects to acquire high-contrast images of SPIONs in a rat model with ULF MRI using short scan times. This work overcomes a key limitation of ULF MRI by enabling in vivo imaging of biocompatible CAs. These results open a new clinical translation pathway for ULF MRI and have broader implications for disease detection with low-field portable MRI scanners.

42 ENGINEERING↗

DOE OSTI2024

Shot-noise-induced lower temperature limit of the nonneutral plasma parallel temperature diagnostic

Abstract We develop a new algorithm to estimate the temperature of a nonneutral plasma in a Penning-Malmberg trap. The algorithm analyzes data obtained by slowly lowering a voltage that confines one end of the plasma and collecting escaping charges, and is a maximum likelihood estimator based on a physically-motivated model of the escape protocol presented in (Beck in Measurement of the magnetic and temperature dependence of the electron-electron anisotropic temperature relaxation rate. PhD thesis, 1990). Significantly, our algorithm may be used on single-count data, allowing for improved fits with low numbers of escaping electrons. This is important for low-temperature plasmas such as those used in antihydrogen trapping. We perform a Monte Carlo simulation of our algorithm, and assess its robustness to intrinsic shot noise and external noise. The assumptions in this paper allow for a lower bound for measurable plasma temperatures of approximately $3\,\mathrm{K}$ 3 K for plasmas of length $1\,\mathrm{cm}$ 1 cm , with approximately 100 particle counts needed for an accuracy of $\pm 10 \%$ ± 10 % .

Zhong, Adrianne (ORCID:0000000162618736)↗

DOE OSTI2022

Hohlraum used as a single turn solenoid to generate seed magnetic field for inertial confinement fusion

Application of axial seed magnetic fields in the range 20-100 T that compress to greater than 10,000 T (100 MG) under typical NIF implosion conditions may significantly relax the conditions required for ignition and propagating burn in NIF ignition targets that are degraded by hydrodynamic instabilities. Such magnetic fields can: (a) permit the recovery of ignition, or at least significant alpha particle heating, in submarginal NIF targets that would otherwise fail because of adverse hydrodynamic instability growth, (b) permit the attainment of ignition in conventional cryogenic layered solid-DT targets redesigned to operate under reduced drive conditions, (c) permit the attainment of volumetric ignition in simpler, room-temperature single-shell DT gas capsules, and (d) ameliorate adverse hohlraum plasma conditions during laser drive and capsule compression. In general, an applied magnetic field should always improve the ignition condition for any NIF ignition target design.

Perkins, Lindsay John↗

DOE OSTI2023

Hohlraum used as a single turn solenoid to generate seed magnetic field for inertial confinement fusion

Perkins, Lindsay John↗

DOE OSTI2020

Magnetic order and disorder in a quasi-two-dimensional quantum Heisenberg antiferromagnet with randomized exchange

In this work, we present an investigation of the effect of randomizing exchange coupling strengths in the S = 1 / 2 square lattice quasi-two-dimensional quantum Heisenberg antiferromagnet (QHAF) ( QuinH ) 2 Cu ( Cl x Br 1 - x ) 4 · 2 H 2 O (QuinH = Quinolinium, C 9 H 8 N + ), with 0 ≤ x ≤ 1 . Pulsed-field magnetization measurements allow us to estimate an effective in-plane exchange strength J in a regime where exchange fosters short-range order, while the temperature T N at which long-range order (LRO) occurs is found using muon-spin relaxation, allowing us to construct a phase diagram for the series. We evaluate the effectiveness of disorder in suppressing T N and the ordered moment size, and we find an extended disordered phase in the region 0.4 ≲ x ≲ 0.8 where no magnetic order occurs. The observed critical substitution levels are accounted for by an energetics-based competition between different local magnetic orders. Furthermore, we demonstrate experimentally that the ground-state disorder is driven by quantum effects of the exchange randomness, which is a feature that has been predicted theoretically and has implications for other disordered quasi-two-dimensional QHAFs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2026

Enhancement of antiferromagnetic spin fluctuations in UTe2 under pressure revealed by 125 Te NMR

Characterizing magnetic fluctuations is one of the keys to understanding the origin of superconductivity in the spin-triplet superconductor UTe 2 , which exhibits two superconducting (SC) phases (SC1 and SC2) under pressure: SC1 where the superconducting transition temperature of 𝑇c decreases with pressure, whereas 𝑇c of SC2 rises with pressure. Previously, D. Ambika et al. [Phys. Rev. B 105, L220403 (2022)] reported the possible coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) spin fluctuations in UTe2 under pressure from their nuclear magnetic resonance (NMR) measurements. To delve into the relationship between the magnetic fluctuations and the two SC phases, we have carried out detailed 125 Te NMR measurements on a single crystal of UTe2 with 𝑇c=1.6K at various pressures ranging from 0 to 2.05 GPa. By comparing the temperature 𝑇 dependence of nuclear spin-lattice relaxation rates divided by temperature 1/𝑇1⁢𝑇 with that of the Knight shift 𝐾 for magnetic fields along the 𝑎, 𝑏, and 𝑐 directions, we evidence the enhancement of AFM spin fluctuations with increasing pressure. Based on the results, we suggest that FM spin fluctuations are more favorable for SC1 and AFM spin fluctuations are crucial for SC2. Our work will inspire further study on this material to understand the peculiar SC phases in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Evaluation of microstructural changes in fresh cement paste using AC impedance spectroscopy vs. oscillation rheology and 1H NMR relaxometry

AC impedance spectroscopy (ACIS) is a promising technique for monitoring the microstructure evolution of fresh cement paste in real-time. This paper compared the change of bulk electric resistivity (ρ{sub bulk}) obtained from ACIS with the developments of storage modulus (G′) and the mean transverse relaxation times (T{sub 2}) of fresh Portland cement pastes within 5 h. It was found that the three different phases (Phase I, II, and III) on the microstructural build-up process of fresh paste can be accurately distinguished by analyzing ρ{sub bulk}, as well as G′ and T{sub 2}. The use of ρ{sub bulk} fails to characterize the microstructural changes in Phase I due to the great sensitivity on the electrical conductivity of the interstitial solution. However, it can successfully reflect the developing features of microstructure in Phases II and III, and reliably evaluate the impacts of water to cement ratio, superplasticizer, and supplementary cementitious materials on the microstructural development.

36 MATERIALS SCIENCE↗