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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Easy axis anisotropy creating high contrast magnetic zones on magnetic tunnel junctions based molecular spintronics devices (MTJMSD)

Abstract Magnetic tunnel junction-based molecular spintronics device (MTJMSD) may enable novel magnetic metamaterials by chemically bonding magnetic molecules and ferromagnets (FM) with a vast range of magnetic anisotropy. MTJMSD have experimentally shown intriguing microscopic phenomenon such as the development of highly contrasting magnetic phases on a ferromagnetic electrode at room temperature. This paper focuses on Monte Carlo Simulations (MCS) on MTJMSD to understand the potential mechanism and explore fundamental knowledge about the impact of magnetic anisotropy. The selection of MCS is based on our prior study showing the potential of MCS in explaining experimental results (Tyagi et al. in Nanotechnology 26:305602, 2015). In this paper, MCS is carried out on the 3D Heisenberg model of cross-junction-shaped MTJMSDs. Our research represents the experimentally studied cross-junction-shaped MTJMSD where paramagnetic molecules are covalently bonded between two FM electrodes along the exposed side edges of the magnetic tunnel junction (MTJ). We have studied atomistic MTJMSDs properties by simulating a wide range of easy-axis anisotropy for the case of experimentally observed predominant molecule-induced strong antiferromagnetic coupling. Our study focused on understanding the effect of anisotropy of the FM electrodes on the overall MTJMSDs at various temperatures. This study shows that the multiple domains of opposite spins start to appear on an FM electrode as the easy-axis anisotropy increases. Interestingly, MCS results resembled the experimentally observed highly contrasted magnetic zones on the ferromagnetic electrodes of MTJMSD. The magnetic phases with starkly different spins were observed around the molecular junction on the FM electrode with high anisotropy.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Magnetic molecules lose identity when connected to different combinations of magnetic metal electrodes in MTJ-based molecular spintronics devices (MTJMSD)

Abstract Understanding the magnetic molecules’ interaction with different combinations of metal electrodes is vital to advancing the molecular spintronics field. This paper describes experimental and theoretical understanding showing how paramagnetic single-molecule magnet (SMM) catalyzes long-range effects on metal electrodes and, in that process, loses its basic magnetic properties. For the first time, our Monte Carlo simulations, verified for consistency with regards to experimental studies, discuss the properties of the whole device and a generic paramagnetic molecule analog (GPMA) connected to the combinations of ferromagnet-ferromagnet, ferromagnet-paramagnet, and ferromagnet-antiferromagnet metal electrodes. We studied the magnetic moment vs. magnetic field of GPMA exchange coupled between two metal electrodes along the exposed side edge of cross junction-shaped magnetic tunnel junction (MTJ). We also studied GPMA-metal electrode interfaces’ magnetic moment vs. magnetic field response. We have also found that the MTJ dimension impacted the molecule response. This study suggests that SMM spin at the MTJ exposed sides offers a unique and high-yield method of connecting molecules to virtually endless magnetic and nonmagnetic electrodes and observing unprecedented phenomena in the molecular spintronics field.

42 ENGINEERING↗
DOE OSTI2019

Effect of oxygen stoichiometry on the magnetization profiles and negative magnetization in LSMO thin films

The depth-dependent magnetization in thin film oxygen stoichiometric and oxygen-deficient La 0.7 Sr 0.3 MnO 3 is investigated by using polarized neutron reflectivity and DC bulk magnetometry. The polarized neutron reflectivity results reveal that the stoichiometric sample shows enhanced interfacial magnetization relative to the rest of the film. The oxygen-deficient sample exhibits a reduced average magnetization from the optimized recipe. Both films show regions of suppressed magnetization at the surface regardless of the growth pressure. The oxygen stoichiometric film does not show an interfacial dead layer, whereas the oxygen-deficient film exhibits a dead layer whose thickness changes with temperature. At a low applied field, we observe striking differences in the depth dependence of the magnetic ordering, with the oxygen-deficient film exhibiting exchange spring behavior, while the stoichiometric film shows a constant magnetization direction across the film. Furthermore, these results suggest that the incorporation of oxygen vacancies during growth leads to an accumulation of vacancies at the interface, which is enhanced at higher temperature due to increased oxygen mobility, creating a region of reduced magnetism that couples to the rest of the film. These results offer insight into the complex behavior and role of oxygen vacancies in the magnetism of these systems. Additionally, the study reveals further details of the negative magnetization in La 0.7 Sr 0.3 MnO 3 reported in previous studies, which are discussed here.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Deep-learning-enabled Bayesian inference of fuel magnetization in magnetized liner inertial fusion

Fuel magnetization in magneto-inertial fusion (MIF) experiments improves charged burn product confinement, reducing requirements on fuel areal density and pressure to achieve self-heating. By elongating the path length of 1.01 MeV tritons produced in a pure deuterium fusion plasma, magnetization enhances the probability for deuterium–tritium reactions producing 11.8-17.1 MeV neutrons. Nuclear diagnostics thus enable a sensitive probe of magnetization. Characterization of magnetization, including uncertainty quantification, is crucial for understanding the physics governing target performance in MIF platforms, such as magnetized liner inertial fusion (MagLIF) experiments conducted at Sandia National Laboratories, Z-facility. We demonstrate a deep-learned surrogate of a physics-based model of nuclear measurements. A single model evaluation is reduced from O ( 10 – 100 ) (10–100) CPU hours on a high-performance computing cluster down to O ( 10 – 100 ) (10) ms on a laptop. This enables a Bayesian inference of magnetization, rigorously accounting for uncertainties from surrogate modeling and noisy nuclear measurements. The approach is validated by testing on synthetic data and comparing with a previous study. We analyze a series of MagLIF experiments systematically varying preheat, resulting in the first ever systematic experimental study of magnetic confinement properties of the fuel plasma as a function of fundamental inputs on any neutron-producing MIF platform. We demonstrate that magnetization decreases from B R ∼ 0.2 ~0.5 to B R ∼ 0.2 ~0.2 MG cm as laser preheat energy deposited increases from E preheat ∼ 460 ~460 J to E preheat ∼ 460 ~1.4 kJ. This trend is consistent with 2D LASNEX simulations showing Nernst advection of the magnetic field out of the hot fuel and diffusion into the target liner.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Effects of chemical pressure on the magnetic ground states of the osmate double perovskites SrCaCoOs 6 and Ca 2 CoOsO 6

The magnetic ground state in the double perovskite system Sr 2-x Ca x CoOsO 6 changes from an antiferromagnet (x=0), to a spin glass (x=1), to a ferrimagnet (x=2) as the Ca content increases. Moreover, this crossover is driven by chemical pressure effects that control the relative strength of magnetic exchange interactions. The synthesis, crystal structure, and magnetism of SrCaCoOsO 6 and Ca 2 CoOsO 6 are investigated and compared with Sr 2 CoOsO 6 . Both compounds adopt a monoclinic crystal structure with rock-salt ordering of Co 2+ and Os 6+ and a - a - b + octahedral tilting, but the average Co–O–Os bond angle evolves from 158.0(3) in SrCaCoOsO 6 to 150.54(9)° in Ca 2 CoOsO 6 as the smaller Ca 2 + ion replaces Sr 2+ . And while this change may seem minor, it has a profound effect on the magnetism, changing the magnetic ground state from antiferromagnetic in Sr 2 CoOsO 6 (TN1=108K, T N2 =70K), to a spin glass in SrCaCoOsO 6 (T f1 =32K, T f2 =13K), to ferrimagnetic in Ca 2 CoOsO 6 (T C =145K). Finally, in the first two compounds the observation of two transitions is consistent with weak coupling between the Co and Os sublattices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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 OSTI2016

Magnetic Materials Characterization and Modeling for the Enhanced Design of Magnetic Shielding of Cryomodules in Particle Accelerators

Particle accelerators produce beams of high-energy particles, which are used for both fundamental and applied scientific research and are critical to the development of accelerator driven sub-critical reactor systems. An effective magnetic shield is very important to achieve higher quality factor (Qo) of the cryomodule of a particle accelerator. The allowed value of field inside the cavity due to all external fields (particularly the Earth’s magnetic field) is ~15 mG or less. The goal of this PhD dissertation is to comprehensively study the magnetic properties of commonly used magnetic shielding materials at both cryogenic and room temperatures. This knowledge can be used for the enhanced design of magnetic shields of cryomodes (CM) in particle accelerators. To this end, we first studied the temperature dependent magnetization behavior (M-H curves) of Amumetal and A4K under different annealing and deformation conditions. This characterized the effect of stress or deformation induced during the manufacturing processes and subsequent restoration of high permeability with appropriate heat treatment. Next, an energy based stochastic model for temperature dependent anhysteretic magnetization behavior of ferromagnetic materials was proposed and benchmarked against experimental data. We show that this model is able to simulate and explain the magnetic behavior of as rolled, deformed and annealed amumetal and A4K over a large range of temperatures. The experimental results for permeability are then used in a finite element model (FEM) in COMSOL to evaluate the shielding effectiveness of multiple shield designs at room temperature as well as cryogenic temperature. This work could serve as a guideline for future design, development and fabrication of magnetic shields of CMs.

Sah, Sanjay↗
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 OSTI2015

Magnetization reversal of a Nd-Cu-infiltrated Nd-Fe-B nanocrystalline magnet observed with small-angle neutron scattering

The magnetization reversal process of Nd-Fe-B nanocrystalline magnets infiltrated with Nd-Cu alloy was examined using small-angle neutron scattering (SANS). The magnetic-field dependence of SANS intensity revealed a qualitative difference between Nd-Cu-infiltrated samples and as-deformed samples. Insufficient magnetic isolation along the direction perpendicular to the nominal c-axis is expected from comparable SANS intensities for different ranges of q values along this direction. For small q values near the coercivity field, Nd-Cu-infiltrated samples show a noticeable reduction in SANS intensity along the nominal c-axis, which is parallel to the external magnetic field. This indicates less spatial fluctuation of magnetic moments in Nd-Cu-infiltrated samples, owing to magnetically isolated Nd{sub 2}Fe{sub 14}B grains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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↗