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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Enhancing interfacial magnetization with a ferroelectric

Ferroelectric control of interfacial magnetism has attracted much attention. However, the coupling of these two functionalities has not been understood well at the atomic scale. The lack of scientific progress is mainly due to the limited characterization methods by which the interface’s magnetic properties can be probed at an atomic level. In this paper, we use polarized neutron reflectometry to probe the evolution of the magnetic moment at interfaces in ferroelectric/strongly correlated oxide [PbZr 0.2 Ti 0.8 O 3 /La 0.8 Sr 0.2 MnO 3 (PZT/LSMO)] heterostructures. We find that the magnetization at the surfaces and interfaces of our LSMO films without PZT are always deteriorated and such magnetic deterioration can be greatly improved by interfacing with a strongly polar PZT film. Magnetoelectric coupling of magnetism and ferroelectric polarization was observed within a couple of nanometers of the interface via an increase in the LSMO surface magnetization to 4.0μ B /f.u., a value nearly 70% higher than the surface magnetization of our LSMO film without interfacing with a ferroelectric layer. We attribute this behavior to hole depletion driven by the ferroelectric polarization. Finally, these compelling results not only probe the presence of nanoscale magnetic suppression and its control by ferroelectrics, but also emphasize the importance of utilizing probing techniques that can distinguish between bulk and interfacial phenomena.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Self-induced magnetic flux structure in the magnetic superconductor RbEuFe 4 As 4

We report an unusual enhancement of the magnetic induction in single crystals of the magnetic superconductor RbEuFe 4 As 4 , highlighting the interplay between superconducting and magnetic subsystems in this material. Contrary to the conventional Meissner expulsion of magnetic flux below the superconducting transition temperature, we observe a substantial boost of the magnetic flux density upon approaching the magnetic transition temperature, T m . Direct imaging of the flux evolution with a magneto-optical technique, shows that the magnetic subsystem serves as an internal magnetic flux pump, drawing Abrikosov vortices from the surface, while the superconducting subsystem controls their conveyance into the bulk of the magnetic superconductor via a peculiar self-organized critical state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Magnetic Field Mapping of a 2.5 T Fixed-Field HTS Gantry Magnet for Proton Therapy

We present results from testing a high-temperature superconducting (HTS) magnet prototype for proton therapy. This magnet is specifically designed for a novel rotating gantry capable of delivering the entire proton beam energy range (70225 MeV) while maintaining a fixed magnetic field in the superconducting magnets. The gantry layout simplifies the magnet design, enabling the use of straight, flat racetrack Bi-2223 (DI-BSCCO) coil technology and operation at higher temperatures (1015 K). The magnet has a non-linear field distribution for bending and focusing the proton beams. To validate this feature, we developed a system for measuring the magnetic field distribution in the magnet aperture. We present the design of this hall probe array and experimental results from two different magnet tests at 4.2 K in a liquid helium bath. These results are compared with the simulated field distribution and discussed in the context of the required field quality for the application.

Mosat, M↗
DOE OSTI2018

Magnetic Structures and Magnetic Phase Transitions in Rare-Earth RMn{sub 2}Si{sub 2} Intermetallic Compounds (R = Sm, Tb)

The magnetic structures that form in La{sub 1–x}R{sub x}Mn{sub 2}Si{sub 2} (R = Sm, Tb) layered compounds with various concentrations x have been determined by magnetic neutron diffraction and magnetic measurements, and the magnetic phase diagrams have been built. It is shown that the formation of the magnetic structures is dependent not only on exchange interactions, but also on the type of the magnetic anisotropy of a rare-earth atom. It is found that, in La{sub 1–x}Tb{sub x}Mn{sub 2}Si{sub 2} compounds with 0.2 < x < 0.5, the competition of the Tb–Mn and Mn–Mn interlayer exchange interactions and the existence of a strong uniaxial magnetic anisotropy in the Mn and Tb sublattices leads to the frustrated magnetic state and prevents the formation of the long-range magnetic order in the Tb sublattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Permanent Magnets for the CEBAF 24GeV Upgrade

An upgrade of the CEBAF facility to double its present energy of 12GeV has been proposed. To provide double the number of linac passes using the existing five stacked arc beamlines, some beamlines are replaced by fixed-field accelerator (FFA) arcs, allowing multiple energies to pass through the same magnets. A solution is presented in which two of the existing electromagnetic beamlines are replaced with permanent magnet non-scaling FFA arcs, as demonstrated at CBETA. The two-stage design reduces peak magnetic field and synchrotron radiation loss compared to using a single stage. FFAs do not pulse their magnets, making permanent magnets a promising and power-efficient technology option. However, the magnetic field requirements are still at the high end of accelerator permanent magnets produced thus far (1.6T peak on beam), while the magnets must also be combined-function, having a gradient with a dipole offset. Designs using a novel oval aperture and open midplane within an adapted Halbach magnet are presented.

Brooks, S. J.↗
DOE OSTI2025

Magnetic Avalanche Detector using Single-Molecule Magnets

Here we discuss the results of the 9 month add-on project: “Magnetic Avalanche Detector using Single-Molecule Magnets”. The key point of the projects was to design a cryogenic system that is capable of applying magnetic fields high enough to magnetize the Single-Molecule Magnets (SMMs), maintain temperatures below 1K, and be able to detect magnetic avalanches of the SMM domains. We were able to achieve these goals. Our system was able to magnetize and sense the magnetization of SMM crystals. Moreover, we were able to detect avalanche demagnetization events caused by an alpha particle interacting with a magnetized SMM.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Coexistence of Magnetic Orders in Two-Dimensional Magnet CrI3

The magnetic properties in two-dimensional van der Waals materials depend sensitively on structure. CrI 3 , as an example, has been recently demonstrated to exhibit distinct magnetic properties depending on the layer thickness and stacking order. Bulk CrI 3 is ferromagnetic (FM) with a Curie temperature of 61 K and a rhombohedral layer stacking, whereas few-layer CrI 3 has a layered antiferromagnetic (AFM) phase with a lower ordering temperature of 45 K and a monoclinic stacking. In this work, we use cryogenic magnetic force microscopy to investigate CrI 3 flakes in the intermediate thickness range (25–200 nm) and find that the two types of magnetic orders, hence the stacking orders, can coexist in the same flake with a layer of ~13 nm at each surface being in the layered AFM phase similar to few-layer CrI 3 and the rest in the bulk FM phase. The switching of the bulk moment proceeds through a remnant state with nearly compensated magnetic moment along the c-axis, indicating formation of c-axis domains allowed by a weak interlayer coupling strength in the rhombohedral phase. Our research provides a comprehensive picture on the magnetism in CrI 3 and point to the possibility of engineering magnetic heterostructures within the same material.

2D magnets↗
DOE OSTI2024

Magnetic Helicity in a Chiral-Polar Magnet Ni 2 InSbO 6

The class of chiral-polar magnets has recently captured significant interest in scientific study due to their intriguing physical phenomena. Among all the chiral-polar magnets, Ni 2 InSbO 6 stands out because of its unique attributes, such as the emergence of the topological chiral soliton lattice in the presence of an external magnetic field perpendicular to the chiral-polar axis. However, the magnetic structure of Ni 2 InSbO 6 at zero field has not been well understood yet. This work presents an analysis including polarized optical microscopy and polarized neutron diffraction on a carefully chosen Ni 2 InSbO 6 crystal. Here, results confirm the predominance of a single chiral-polar domain within the crystal and indicate the likelihood of cycloidal magnetic ordering under zero magnetic field, alongside the observation of net magnetic helicity. The existence of both a dominant chiral-polar domain and a dominant cycloidal magnetic domain within Ni 2 InSbO 6 provides an excellent platform for further exploration of its unconventional physical attributes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

A Kinetic Inductance Ammeter with Coplanar Waveguide Input Structure for Magnetic Flux Focusing

We propose a multiplexible kinetic inductance ammeter, which uses a high-quality-factor, superconducting, lumped-element, kinetic inductance resonator as a current sensor, a short, superconducting coplanar waveguide (CPW) for current input, and a CPW transmission line for the sensor readout. The resonator consists of an interdigitated capacitor and a superconducting loop that inductively couples to the input CPW. Current running through the central line of the input CPW generates magnetic fields which are focused into the gaps of the input CPW. These magnetic fields can be measured collectively as the magnetic flux through the superconducting loop. The kinetic inductance of the superconducting loop depends on the screening current for the magnetic flux, so the input current is converted to a change in the frequency of the resonator. We analyze the response and noise of a kinetic inductance ammeter with a high-resistivity NbN loop.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Dependence of the Magnetic Transition Temperatures T{sub N1} and T{sub N2} and Magnetization Plateau of the 2D Checkerboard Lattice Structure with the Superblock (N,N)

Magnetic properties of the 2D checkerboard lattice structure with the superblock (N,N) were studied using Monte Carlo simulation based on the Ising model. Thermal magnetization and magnetic susceptibility of 2D checkerboard lattice with several superblocks are given. Two magnetic anomalies at collinear-to-spiral transition temperature t{sub C1} and transition temperature t{sub C2}have been determined. We discuss the effect of exchange interactions and superblocks on 2D checkerboard lattice. Magnetic hysteresis cycle of 2D checkerboard lattice for several superblocks have been shown. Superparamagnetic behaviour has been observed. Magnetization plateau, visible as anomalies in magnetic hysteresis, is one of the hallmarks of frustrated magnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic and Thermal Design of HTS Quadrupole Magnet for Newly Developed Superconducting Proton Cyclotron Beam Line

A magnetic and thermal design of high-temperature superconducting (HTS) quadrupole magnet for newly developed superconducting proton cyclotron was presented in this research. With superconducting technology, the design can reduce the magnet size and remove the heat loads more efficiently. Calculations are conducted with finite element method (FEM) to study the quadrupole magnet’s magnetic and thermal properties. For the magnet cold-mass and cryostat system, the heat load is mainly generated by conduction and radiation. Multilayer thermal insulation and G10 supports are used to restrict them. The magnetic field distribution in the HTS coils is calculated to consider the critical current degradation of the YBCO tapes. The effects on the field gradient quality in relation to the pole tip profile and end chamfer are analyzed. The sixth multipole component in the integral field can be improved with end chamfer. Finally, a 20 T/m HTS quadrupole magnet with integral field uniformity less than 0.05% out to 75% of the inscribed radius is proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

In this work, we investigated the ambient temperature structural properties (~300 K) and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties of melt-spun Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The thickness, width, lattice parameter, saturation magnetization (MS), and intrinsic coercivity (HCI) of the melt spun ribbons are presented and compared with data in the literature. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbons ranged between ~15-60 μm and 500-800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel-surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). Wheel surface speed was not shown to have a significant effect on the magnetization, but primarily impacted the ribbon structure. A decreasing trend in the saturation magnetization was observed as a function of increased silicon content. The intrinsic coercivity of the melt-spun alloys ranged between ~50 to 200 A/m. Elevated temperature evaluation of the magnetization in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The MS for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 – 900 K). The percentage decrease in MS from 300 K to 900 K for the Fe-3 wt.% Si and Fe-5 wt.% Si alloys was ~19-22 %, while the percentage decrease in the same temperature range for Fe-8 wt.% Si alloy was ~26-30 %. It appears that Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) with any minor constituents being beyond the detection limits of the studies performed, while the Fe-8 wt.% Si alloy ribbons are comprised of disordered and regions of short-range ordering.

Elevated Temperature↗
DOE OSTI2022

Mechanically robust high magnetic-performance Sm-Co sintered magnets through microstructure engineering

Samarium-cobalt (Sm-Co) sintered magnets have high magnetic energy densities, great resistance to demagnetization and corrosion, and excellent thermal stability in a wide temperature range (–50–550 °C). However, the utilization of these magnets is restricted by their brittleness. Based on micromechanical and the Zener pinning model, Sm-Co sintered magnets with improved mechanical properties have been designed and fabricated via microstructure engineering. A small amount of fine Sm 2 O 3 particulates (0–3 wt%) has been incorporated into Sm 2 (CoFeCuZr) 17 sintered magnets to refine the grain size by up to approximately 50% (from 45 to 22 µm) and narrow the grain size distribution. Doping with 3 wt% Sm 2 O 3 increased the flexural strength by 62% while maintaining magnetic performance. Both grain-refined unimodal microstructure and heterogeneous laminated coarse/fine grain microstructure were formed by strategically designed assemblies of Sm 2 O 3 -added Sm-Co powder feedstock mixtures. The technology is compatible with existing magnet manufacturing processes. Numerical micromechanics simulation indicates that the fracture is dominated by intragranular mode. The mechanical strength is mainly enhanced by the additive-induced grain refinement, while the small amount of Sm 2 O 3 addition has a small direct positive contribution. Finally, these magnets will be more cost-effective, efficient, and robust for various functional applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effects of magnetic field annealing on the hard magnetic properties of milled Nd-Fe-B powders

In this study, we report the effect of magnetic field annealing (MA) in relieving the stress induced during the milling of Nd-Fe-B sintered magnets. The effect of MA processing parameters and particle size on the magnetic properties were investigated. Based on the results, magnetic field annealing is more effective in improving the magnetic properties of larger size particles, compared to finer particles. Our computational study on the role of particle surface defects in bi-modal particle distribution agrees with results obtained experimentally. In conclusion, magnetic field annealed powder has been successfully used to develop 4.6 g.cm -3 density bonded magnets with 75 vol% of magnetic powder and polyamide 12 (nylon 12) polymer binder resulting in 11.3 MGOe energy product.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Magnetic force microscopy revealing long range molecule impact on magnetic tunnel junction based molecular spintronics devices

Magnetic force microscopy (MFM) vividly showed that organometallic molecules, when bridged between two ferromagnetic electrodes along the cross-shaped magnetic tunnel junction edges transformed the magnetic electrodes itself. Molecules impacted a large area of ferromagnetic leads around the junction at room temperature and complement the previous magnetic measurements showing molecule effect on pillar form magnetic tunnel junctions. This molecule induced changes in the magnetic electrodes impacted the transport of the magnetic tunnel junction and stabilized as much as seven orders smaller current at room temperature. We have discussed the current suppression phenomenon in the recent publication [Ref. Tyagi et al. Organic Electronics, 2019, Vol. 64, p 188]; however, we did not provide any direct evidence of molecule impact on ferromagnetic electrodes around molecule junction. Our MFM studies in this paper suggests that molecule effect was observable several μm away from the molecule-metal junctions. Furthermore, our study suggests that magnetic tunnel junction based molecular spintronics devices can be a gateway to a vast range of commercially viable and robust futuristic computer devices and highly correlated materials.

42 ENGINEERING↗