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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Surface-Engineered MXenes: Electric Field Control of Magnetism and Enhanced Magnetic Anisotropy

Controlling magnetism in two-dimensional (2D) materials via electric fields and doping enables robust long-range order by providing an external mechanism to modulate magnetic exchange interactions and anisotropy. Here in this report, we predict that transition metal carbide and nitride MXenes are promising candidates for controllable magnetic 2D materials. The surface terminations introduced during synthesis act as chemical dopants that influence the electronic structure, enabling controllable magnetic order. We show ground-state magnetic ordering in Janus M 2 XO x F 2–x (M is an early transition metal, X is carbon or nitrogen, and x = 0.5, 1, or 1.5) with asymmetric surface functionalization, where local structural and chemical disorder induces magnetic ordering in some systems that are nonmagnetic or weakly magnetic in their pristine form. The resulting magnetic states of these noncentrosymmetric structures can be robustly switched and stabilized by tuning the interlayer exchange couplings with small applied electric fields. Furthermore, bond directionality is enhanced by Janus functionalization, resulting in improved magnetic anisotropy, which is essential to stable 2D magnetic ordering. The mixed termination-induced anisotropy leads to robust Ising ferromagnetism with an out-of-plane easy axis over the full range of relevant termination compositions for Janus Mn 2 N. Janus Cr 2 C, V 2 C, and Ti 2 C were found to be robustly antiferromagnetic. Our results provide a strategy for exploiting asymmetric surface functionalization to achieve room-temperature nanoscale magnetism under ambient conditions in MXenes with currently available synthesis techniques.

2D materials↗
DOE OSTI2020

Strong surface magnetic field generation in relativistic short pulse laser–plasma interaction with an applied seed magnetic field

Abstract While plasma often behaves diamagnetically, we demonstrate that the laser irradiation of a thin opaque target with an embedded target-transverse seed magnetic field B seed can trigger the generation of an order-of-magnitude stronger magnetic field with opposite sign at the target surface. Strong surface field generation occurs when the laser pulse is relativistically intense and results from the currents associated with the cyclotron rotation of laser-heated electrons transiting through the target and the compensating current of cold electrons. We derive a predictive scaling for this surface field generation, B gen ∼ −2 πB seed Δ x / λ 0 (in the large spot size limit), where Δ x is the target thickness and λ 0 is the laser wavelength, and conduct 1D and 2D particle-in-cell simulations to confirm its applicability over a wide range of conditions. We additionally demonstrate that both the seed and surface-generated magnetic fields can have a strong impact on application-relevant plasma dynamics, for example substantially altering the overall expansion and ion acceleration from a μ m-thick laser-irradiated target with a kilotesla-level seed magnetic field.

Weichman, K. (ORCID:0000000234877922)↗
DOE OSTI2022

Second-order magnetic responses in quantum magnets: Magnetization under ac magnetic fields

Here we investigate second-order magnetic responses of quantum magnets against ac magnetic fields. We focus on the case where the z component of the spin is conserved in the unperturbed Hamiltonian and the driving field is applied in the xy plane. We find that linearly polarized driving fields induce a second-harmonic response, while circularly polarized fields generate only a zero-frequency response, leading to a magnetization with a direction determined by the helicity. Employing an unbiased numerical method, we demonstrate the nonlinear magnetic effect driven by the circularly polarized field in the XXZ model and show that the magnitude of the magnetization can be predicted by the dynamical spin structure factor in the linear response regime.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Quantum Imaging of Magnetic Phase Transitions and Spin Fluctuations in Intrinsic Magnetic Topological Nanoflakes

Topological materials featuring exotic band structures, unconventional current flow patterns, and emergent organizing principles offer attractive platforms for the development of next-generation transformative quantum electronic technologies. The family of MnBi 2 T e4 (Bi 2 Te 3 )n materials is naturally relevant in this context due to their nontrivial band topology, tunable magnetism, and recently discovered extraordinary quantum transport behaviors. Despite numerous pioneering studies, to date, the local magnetic properties of MnBi 2 Te 4 (Bi 2 Te 3 )n remain an open question, hindering a comprehensive understanding of their fundamental material properties. Exploiting nitrogen-vacancy (NV) centers in diamond, we report nanoscale quantum imaging of magnetic phase transitions and spin fluctuations in exfoliated MnBi 2 Te 4 (Bi 2 Te 3 )n flakes, revealing the underlying spin transport physics and magnetic domains at the nanoscale. Furthermore, our results highlight the unique advantage of NV centers in exploring the magnetic properties of emergent quantum materials, opening new opportunities for investigating the interplay between topology and magnetism.

Antiferromagnetic materials↗
DOE OSTI2019

Tunable Magnetic Transition to a Singlet Ground State in a 2D van der Waals Layered Trimerized Kagomé Magnet

Incorporating magnetism into two-dimensional (2D) van der Waals (vdW) heterostructures is crucial for the development of functional electronic and magnetic devices. Here, we show that Nb 3 X 8 (X = Cl, Br) is a family of 2D layered trimerized kagomé magnets that are paramagnetic at high temperatures and undergo a first-order phase transition on cooling to a singlet magnetic state. X-ray diffraction shows that a rearrangement of the vdW stacking accompanies the magnetic transition, with high- and low-temperature phases consistent with scanning transmission electron microscopy images of the end members α-Nb 3 Cl 8 and β-Nb 3 Br 8 . The temperature of this transition is systematically varied across the solid solution Nb 3 Cl 8–x Br x (x = 0–8), with x = 6 having transitions near room temperature. Furthermore, the solid solution also varies the optical properties, which are further modulated by the phase transition. As such, they provide a platform on which to understand and exploit the interplay between dimensionality, magnetism, and optoelectronic behavior in vdW materials.

2D materials↗
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↗
DOE OSTI2024

Advanced Permanent Magnet Generator Topologies Using Multimaterial Shape Optimization and 3D Printing: Preprint

A vast majority of utility-scale wind turbine generators in the United States are dependent on foreign- sourced rare-earth permanent magnets that are vulnerable to supply chain uncertainties. Many small wind original equipment manufacturers are motivated to pursue continuous improvements to the generator design to lower the material and production costs and improve performance by lowering cogging torque and increasing the efficiency. Traditional design and manufacturing offer limited opportunities. In this work, we demonstrate advanced design approaches for a 15-kW baseline wind turbine generator by making use of recent progress in three-dimensional (3D) printing of polymer- bonded magnets and, electrical and structural steel. We explore three methods of magnet parametrization using Bezier curves resulting in symmetric, asymmetric and multimaterial magnet designs. We employ a multiphysics approach combining parametric computer-aided design modeling, finite- element analysis and targeted sampling to identify novel designs with more opportunities for reducing rare-earth material, improving efficiency and minimizing cogging torque. The results show that asymmetric-pole design and multimaterial-pole designs offer a greater opportunity to minimize rare-earth magnet materials by up to 35% with similar performance as the baseline generator, suggesting newer opportunities with design freedom beyond traditional limits of symmetry and as allowed by 3D printing.

Bezier curves↗
DOE OSTI2023

An Assessment of Additively Manufactured Bonded Permanent Magnets for a Distributed Wind Generator

In this paper, we examine and compare the performance of a generator design optimized using additively manufactured NdFeB-SmFeN in nylon-polymer-bonded permanent magnets (PMs) against a generator design with conventional NdFeB sintered PMs. To realize this, a commercially available 15-kW wind generator's rotor is re-optimized using both additively manufactured and sintered NdFeB magnets using simple geometric parameterization that allowed for two specific magnet shapes, namely, arc-shaped and crown-shaped designs. Results showed that for a similar generator performance, the designs with additively manufactured bonded PMs are more cost-competitive in terms of the estimated PM material cost and also have negligible eddy current magnet losses.

additive manufacturing↗
DOE OSTI2020

The effect of magnetic susceptibility and magnetic field strength on porosity estimates determined from low-field nuclear magnetic resonance

The presence of materials with high magnetic susceptibility are known to have an impact on 1H nuclear magnetic resonance (NMR) measurements and in laboratory data this often results in poor estimates of porosity from NMR data. To quantify and understand the cause of the poor NMR porosity estimations, in this laboratory study, we examine the effect of magnetic susceptibility, NMR measurement parameters, and NMR instrument design on NMR measurements. Data were collected with two instruments, each with a different Larmor frequency (2 MHz and 485 kHz), on water-saturated unconsolidated sediments with magnetic susceptibility values ranging from 3.6 × 10 -6 to 7020 × 10 -6 SI. The results show that for materials with low magnetic susceptibility (<378 × 10 -6 SI), the gravimetric porosity is accurately predicted from the NMR measurements. For the samples with high magnetic susceptibility (>987 × 10 -6 SI) the gravimetric porosity is poorly predicted from the 2 MHz NMR measurements made at all echo times (from 0.2 to 3.0 ms). In contrast, the gravimetric porosity is more accurately predicted at an echo time of 0.2 ms for measurements made using the 485 kHz instrument, although at larger echo times (>1.0 ms), the porosity estimate becomes poor. The 485 kHz NMR instrument has non-zero internal magnetic field gradients, similar to those found in borehole instruments, in contrast to the 2 MHz NMR instrument, which has a homogeneous applied magnetic field. Finally, we conclude that differences is the magnetic field strength and higher magnetic field inhomogeneities in the 485 kHz NMR instrument contribute to a reduction of the impact of inhomogeneities in the magnetic field caused by materials with high magnetic susceptibility, allowing for improved porosity estimation. These results indicate that NMR measurements collected at short echo times in low, inhomogeneous static fields, e.g., borehole instruments, may provide accurate estimates of porosity in water saturated sediments, even in the presence of magnetic minerals.

58 GEOSCIENCES↗
DOE OSTI2020

A High-Speed High-Power-Density Non-Heavy Rare-Earth Permanent Magnet Traction Motor

There has been a global push for higher torque density and lower cost traction motors. The use of non-heavy rare-earth (non-HRE) permanent magnet materials in traction motors are being investigated for the sustainability, profitability and affordability of electric vehicles and to broaden their adoption. A 20,000-rpm permanent magnet traction motor using non-HRE magnet materials is proposed. A dual three-phase winding configuration driven by a segmented dual three-phase drive is proposed to reduce the current ripple, and as a result, the DC Link capacitor, as well as to ease the voltage constraint at high speed and eliminate any risk of uncontrolled regeneration. Furthermore, the dual winding configuration enables a fault tolerant design which is useful for reliability. The paper presents comprehensive electromagnetic, thermal and mechanical designs and analyses using an integrated approach. The results have shown that the design is robust against demagnetization and confirmed its thermal and mechanical viability.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Direct visualization of magnetic domains and moiré magnetism in twisted 2D magnets

Moiré superlattices of twisted nonmagnetic two-dimensional (2D) materials are highly controllable platforms for the engineering of exotic correlated and topological states. In this work, we report emerging magnetic textures in small-angle twisted 2D magnet chromium triiodide (CrI 3 ). Using single-spin quantum magnetometry, we directly visualized nanoscale magnetic domains and periodic patterns, a signature of moiré magnetism, and measured domain size and magnetization. In twisted bilayer CrI 3 , we observed the coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) domains with disorder-like spatial patterns. In twisted double-trilayer CrI 3 , AFM and FM domains with periodic patterns appear, which is in good agreement with the calculated spatial magnetic structures that arise from the local stacking-dependent interlayer exchange interactions in CrI 3 moiré superlattices. Our results highlight magnetic moiré superlattices as a platform for exploring nanomagnetism.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Design and Comparison of Surface Inset Permanent Magnet Machine and Surface Permanent Magnet Machine without Heavy Rare Earth Magnets for Traction Applications

This paper presents two machine designs: a surface inset permanent magnet (SIPM) machine and a surface permanent magnet (SPM) machine, both without heavy rare-earth magnets, that achieve 50 kW/L active power density and a constant-power speed ratio of 3 for EV traction applications. Compared to surface PM machines, SIPM machines do not require a special containment sleeve to hold the magnets in place at high speeds, provided that the rotor laminations are carefully designed together with the magnet mounting configuration to ensure the rotor’s structural integrity. Comparisons between the SPM and SIPM machines sharing the same stator, same current level, and same power speed envelope are presented. Both deliver very similar performance characteristics, but the SIPM machine’s simpler magnet containment configuration may give it an advantage in terms of reduced material and manufacturing costs.

42 ENGINEERING↗
DOE OSTI2019

Observation of a Large Magnetic Anisotropy and a Field-Induced Magnetic State in SrCo(VO 4 )(OH): A Structure with a Quasi One-Dimensional Magnetic Chain

A new member of the descloizite family, a cobalt vanadate, SrCo(VO 4 )(OH), has been synthesized as large single crystals using high-temperature and high-pressure hydrothermal methods. SrCo(VO 4 )(OH) crystallizes in the orthorhombic crystal system in space group P 2 1 2 1 2 1 with the following unit cell parameters: a = 6.0157(2) Å, b = 7.645(2) Å, c = 9.291(3) Å, V = 427.29(2) Å 3 , and Z = 4. It contains one-dimensional Co–O–Co chains of edge-sharing CoO 6 octahedra along the a -axis connected to each other via VO 4 tetrahedra along the b -axis forming a three-dimensional structure. The magnetic susceptibility of SrCo(VO 4 )(OH) indicates an antiferromagnetic transition at 10 K as well as unusually large spin orbit coupling. Single-crystal magnetic measurements in all three main crystallographic directions displayed a significant anisotropy in both temperature- and field-dependent data. Single-crystal neutron diffraction at 4 K was used to characterize the magnetically ordered state. The Co 2+ magnetic spins are arranged in a staggered configuration along the chain direction, with a canting angle that follows the tipping of the CoO 6 octahedra. The net magnetization along the chain direction, resulting in ferromagnetic coupling of the a -axis spin components in each chain, is compensated by an antiferromagnetic interaction between nearest neighbor chains. A metamagnetic transition appears in the isothermal magnetization data at 2 K along the chain direction, which seems to correspond to a co-alignment of the spin directions of the nearest neighbor chain. We propose a phenomenological spin Hamiltonian that describes the canted spin configuration of the ground state and the metamagnetic transition in SrCo(VO 4 )(OH).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Correlation between Epitaxial Strain and Magnetic Properties in La0.7Sr0.3CoO3/La0.7Sr0.3MnO3 bilayers

Magnetic properties arising at interfaces of perovskite oxides such as La0.7Sr0.3MnO3 (LSMO) and La0.7Sr0.3CoO3 (LSCO) depend sensitively on the fine details of their structural properties. In this work, we use high-resolution transmission electron microscopy and spectroscopy to examine the structural and electronic phenomena at the interfaces in two LSMO/LSCO bilayers with reversed growth order. Two different strain mechanisms are at work in these films; compressive or tensile epitaxial strain, and distortion of the octahedral tilt pattern to maintain the network of corner-sharing octahedra. While the epitaxial strain is constant, regardless of growth order, the modification of the octahedral tilt pattern depends on whether the film is grown directly on the substrate, or as the second sublayer. As a consequence, exchange spring behavior is observed only when the LSCO sublayer is grown first. The different mechanisms of strain accommodation within the oxygen octahedra network in each material prove to be of critical importance in determining the interfacial structure and thus magnetic and electronic properties of the bilayers.

perovskites, interfaces, microscopy, magnetism↗
DOE OSTI2025

Magnetic force microscopy revealing long-range room temperature stable molecule bridge-induced magnetic ordering on magnetic tunnel junction (MTJ) pillars

Magnetic tunnel junctions (MTJs) can integrate novel single molecular device elements to overcome long-standing fabrication challenges, thus unlocking their novel potential. This study employs magnetic force microscopy (MFM) to demonstrate that organometallic molecules, when placed between two ferromagnetic electrodes along cross-junction shaped MTJ edges, dramatically altered the magnetic properties of the electrodes, affecting areas several hundred microns in size around the molecular junction vicinity at room temperature. These findings are supported by magnetic resonance and magnetometer studies on ∼7000 MTJ pillars. MFM on the pillar sample showed an almost complete disappearance of the magnetic contrast. The spatial magnetic image suggests that molecular channels significantly impacted the spin density of states in the ferromagnetic electrodes. This advancement in MTJ-based molecular devices paves the way for a new generation of commercially viable logic and memory devices controlled by molecular quantum states at near-room temperatures.

Tyagi, Pawan (ORCID:0000000275411344)↗