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All sources NASA NTRS DOE OSTI

DOE OSTI2019

Investigation of Powder Processing, Heat Treating, and Texturing to Improve Gas Atomized alnico Magnets for use in Electric Drive Motors

Alnico permanent magnet materials have been proposed as a rare earth free permanent magnet alternative during an ongoing search to replace rare earth permanent magnets that are used for interior permanent magnet motors, a common motor found in electric vehicles. A powder processing approach was used to study two alnico alloys (Full-Co and lower cost Co-Lean, both with enhanced coercivity) to anticipate high volume manufacturing needed to supply millions of permanent magnets to interior permanent magnet motors. In this study the two alloys were gas atomized, compression molded, and solid-state sintered to fabricate near-final shape alnico magnets. The Full-Co displayed abnormal grain growth (resulting in >1 mm size grains) during sintering while the Co-Lean did not (~20 μm – 400 μm sized grains depending on the sintering hold times). Solid state grain alignment was used to promote a <001> textured (easy axis) microstructure to enhance magnetic properties, yet both alloys did not show predicted grain alignment behavior. Comparisons of the powder processing, microstructures, and magnetic properties of the two alloys will be discussed, as well as an evaluation as to why non-theoretical processing behavior of the Full-Co and Co-Lean alnico permanent magnets is occurring. Preliminary interior permanent magnet motor designs for alnico magnets are discussed, as this is the overarching objective for powder-based alnico permanent magnets.

Rinko, Emily↗

DOE OSTI2019

Enhancement of interlayer exchange in an ultrathin two-dimensional magnet

Following the recent isolation of monolayer CrI 3 , many more two-dimensional van der Waals magnetic materials have been isolated. Their incorporation in van der Waals heterostructures offers a new platform for spintronics, proximity magnetism and quantum spin liquids. A primary question in this field is how exfoliating crystals to the few-layer limit influences their magnetism. Studies of CrI 3 have shown a different magnetic ground state for ultrathin exfoliated films compared with the bulk, but the origin is not yet understood. Here, we use electron tunnelling through few-layer crystals of the layered antiferromagnetic insulator CrCl 3 to probe its magnetic order and find a tenfold enhancement of the interlayer exchange compared with bulk crystals. Moreover, temperature- and polarization-dependent Raman spectroscopy reveals that the crystallographic phase transition of bulk crystals does not occur in exfoliated films. This results in a different low-temperature stacking order and, we hypothesize, increased interlayer exchange. In conclusion, our study provides insight into the connection between stacking order and interlayer interactions in two-dimensional magnets, which may be relevant for correlating stacking faults and mechanical deformations with the magnetic ground states of other more exotic layered magnets such as RuCl 3 .

36 MATERIALS SCIENCE↗

DOE OSTI2017

Magnetic switching in granular FePt layers promoted by near-field laser enhancement

Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle X-ray scattering at an X-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, 1 order of magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between “up” and “down” magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. Furthermore, the fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Giant low-field magnetocaloric effect and refrigerant capacity in reduced dimensionality EuTiO 3 multiferroics

Engineering magnetic materials into a thin film form while preserving its excellent magnetocaloric response is essential in the development of miniature magnetic coolers. We demonstrate how this can be achieved in the case of EuTiO 3 - an emerging multiferroic material. Unlike conventional cases where reduced dimensionality considerably decreased the magnetic entropy change (ΔS M ) and hence the refrigerant capacity (RC), we show the large low-field enhancements of ΔS M and RC in a ~100 nm thick nanocrystalline EuTiO 3 film (ΔS M ~ 24 J kg -1 K -1 and RC = 152 J kg -1 for μ 0 ΔH = 2T) relative to its single crystal counterpart (ΔS M ~ 17 J kg -1 K -1 and RC ~ 107 J kg -1 for μ 0 ΔH = 2T). The nanocrystalline EuTiO 3 film is an excellent candidate for cryogenic magnetic refrigeration. From our study, a new approach for improving both MCE and RC in magnetic nanomaterials is proposed, which will stimulate further research on magnetocaloric thin films and related cooling devices.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Silverland: the Realm of Compounds of Divalent Silver—and Why They are Interesting

In this personal account, the author takes readers on the journey to “Silverland,” i.e., the emerging field of electronic and magnetic materials based on divalent silver (Ag{sup 2+}). He blends historical background with the reasons which led him to become involved in this research, as well as to proposing (with Roald Hoffmann, 2001) that high-T{sub C} superconductivity might ultimately be observed in doped Ag{sup 2+} fluorides. More recent experimental and theoretical findings related to novel compounds, and their electronic and magnetic structure, are presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1991

Finite difference time domain electromagnetic scattering from frequency-dependent lossy materials

Four different FDTD computer codes and companion Radar Cross Section (RCS) conversion codes on magnetic media are submitted. A single three dimensional dispersive FDTD code for both dispersive dielectric and magnetic materials was developed, along with a user's manual. The extension of FDTD to more complicated materials was made. The code is efficient and is capable of modeling interesting radar targets using a modest computer workstation platform. RCS results for two different plate geometries are reported. The FDTD method was also extended to computing far zone time domain results in two dimensions. Also the capability to model nonlinear materials was incorporated into FDTD and validated.

Luebbers, Raymond J.↗

DOE OSTI2015

Emergent reduced dimensionality by vertex frustration in artificial spin ice

Reducing the dimensionality of a physical system can have a profound effect on its properties, as in the ordering of low-dimensional magnetic materials, phonon dispersion in mercury chain salts, sliding phases, and the electronic states of graphene. Here we explore the emergence of quasi-one-dimensional behaviour in two-dimensional artificial spin ice, a class of lithographically fabricated nanomagnet arrays used to study geometrical frustration. We extend the implementation of artificial spin ice by fabricating a new array geometry, the so-called tetris lattice. We demonstrate that the ground state of the tetris lattice consists of alternating ordered and disordered bands of nanomagnetic moments. The disordered bands can be mapped onto an emergent thermal one-dimensional Ising model. Furthermore, we show that the level of degeneracy associated with these bands dictates the susceptibility of island moments to thermally induced reversals, thus establishing that vertex frustration can reduce the relevant dimensionality of physical behaviour in a magnetic system.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Controlling topology through targeted composite symmetry manipulation in magnetic systems

The possibility of selecting magnetic space groups by orienting the magnetization direction or tuning magnetic orders offers a vast playground for engineering symmetry-protected topological phases in magnetic materials. In this work, we study how selective tuning of symmetry and magnetism can influence and control the resulting topology in a two-dimensional magnetic system, and we illustrate such a procedure in the ferromagnetic monolayer MnPSe 3 . Density functional theory calculations reveal a symmetry-protected accidental semimetallic (SM) phase for out-of-plane magnetization, which becomes an insulator when the magnetization is tilted in-plane, reaching band-gap values close to 100 meV. We identify an order-2 composite antiunitary symmetry and threefold rotational symmetry that induce the band crossing, and we classify the possible topological phases using symmetry analysis, which we support with tight-binding and k · p models. Breaking of inversion symmetry opens a gap in the SM phase, giving rise to a Chern insulator. We demonstrate this explicitly in the isostructural Janus compound Mn 2 ⁢P 2 ⁢S 3 ⁢Se 3 , which naturally exhibits Rashba spin-orbit coupling that breaks inversion symmetry. Our results map out the phase space of topological properties of ferromagnetic transition-metal phosphorus trichalcogenides, and they demonstrate the potential of the magnetization-dependent metal-to-insulator transition as a spin switch in integrated two-dimensional electronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Engineering Topological Superlattices and Phase Diagrams

The search for new topological materials and states of matter is presently at the forefront of quantum materials research. One powerful approach to novel topological phases beyond the thermodynamic space is to combine different topological/functional materials into a single materials platform in the form of superlattices. However, despite some previous efforts there has been a significant gap between theories and experiments in this direction. Here in this paper, we provide the first detailed set of experimentally verifiable phase diagrams of topological superlattices composed of archetypal topological insulator, Bi 2 Se 3 , and normal insulator, In 2 Se 3 , by combining molecular-level materials control, low-temperature magnetotransport measurements, and field theoretical calculations. We show how the electronic properties of topological superlattices evolve with unit-layer thicknesses and utilize the weak antilocalization effect as a tool to gain quantitative insights into the evolution of conducting channels within each set of heterostructures. This orchestrated study opens the door to the possibility of creating a variety of artificial-topological-phases by combining topological materials with various other functional building blocks such as superconductors and magnetic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2017

Intrinsic magnetism and spontaneous band gap opening in bilayer silicene and germanene

It has been long sought to create magnetism out of simple non-magnetic materials, such as silicon and germanium. Here we show that intrinsic magnetism exists in bilayer silicene and germanene with no need to cut, etch, or dope. Unlike bilayer graphene, strong covalent interlayer bonding formed in bilayer silicene and germanene breaks the original π-bonding network of each layer, leaving the unbonded electrons unpaired and localized to carry magnetic moments. These magnetic moments then couple ferromagnetically within each layer while antiferromagnetically across two layers, giving rise to an infinite magnetic sheet with structural integrity and magnetic homogeneity. Furthermore, this unique magnetic ordering results in fundamental band gaps of 0.55 eV and 0.32 eV for bilayer silicene and germanene, respectively. The integration of intrinsic magnetism and spontaneous band gap opening makes bilayer silicene and germanene attractive for future nanoelectronics as well as spin-based computation and data storage.

Wang, Xinquan↗

DOE OSTI2015

Design and Implementation of a Hall Effect Sensor Array Applied to Recycling Hard Drive Magnets

Rare earths are an important resource for many electronic components and technologies. Examples abound including Neodymium magnets used in mobile devices and computer hard drives (HDDs), and a variety of renewable energy technologies (e.g., wind turbines). Approximately 21,000 metric tons of Neodymium is processed annually with less than 1% being recycled. An economic system to assist in the recycling of magnet material from post-consumer goods, such as Neodymium Iron Boron magnets commonly found in hard drives is presented. A central component of this recycling measurement system uses an array of 128 Hall Effect sensors arranged in two columns to detect the magnetic flux lines orthogonal to the HDD. Results of using the system to scan planar shaped objects such as hard drives to identify and spatially locate rare-earth magnets for removal and recycling from HDDs are presented. Applications of the sensor array in other identification and localization of magnetic components and assemblies will be presented.

Hall Effect sensors↗

DOE OSTI2022

Donor–Acceptor Conjugated Copolymers Containing Transition-Metal Complex: Intrachain Magnetic Exchange Interactions and Magneto-Optical Activity

A donor-acceptor conjugated copolymer containing thienothiophene (TT) (Donor) units and Co(II) complexes (Acceptor) has been synthesized and characterized. The studies of magnetic properties of the polymers by SQUID and EPR measurements showed antiferromagnetic exchange interaction between neighboring spin centers along with the polymer backbone through intrachain in-teractions. It is the first time that D-A conjugated polymer backbone serving as bridging ligands for magnetic couplings, making this type of polymers promising as magnetic materials. Moreover, the magneto-optical activity (MOA) of polymer LCP1 was char-acterized using magnetic circular dichroism (MCD) spectroscopy. It was found that the material exhibits a large magneto-optic rotation with a peak Verdet constant of 2980 deg*T -1 *m -1 at 590 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1985

Energy and momentum management of the Space Station using magnetically suspended composite rotors

The research addresses the feasibility of using magnetically suspended composite rotors to jointly perform the energy and momentum management functions of an advanced manned Space Station. Recent advancements in composite materials, magnetic suspensions, and power conversion electronics have given flywheel concepts the potential to simultaneously perform these functions for large, long duration spacecraft, while offering significant weight, volume, and cost savings over conventional approaches. The Space Station flywheel concept arising out of this study consists of a composite-material rotor, a large-angle magnetic suspension (LAMS) system, an ironless armature motor/generator, and high-efficiency power conversion electronics. The LAMS design permits the application of appropriate spacecraft control torques without the use of conventional mechanical gimbals. In addition, flywheel systems have the growth potential and modularity needed to play a key role in many future system developments.

Eisenhaure, D. B.↗

DOE OSTI2019

Disentangling spin-orbit coupling and local magnetism in a quasi-two-dimensional electron system

Quantum interference between time-reversed electron paths in two dimensions (2D) leads to the well-known weak localization correction to resistance. If spin-orbit coupling is present, the resistance correction is negative, termed weak antilocalization (WAL). Here, we report the observation of WAL coexisting with exchange coupling between itinerant electrons and localized magnetic moments. We use low-temperature magnetotransport measurements to investigate the quasi-two-dimensional, high-electron-density interface formed between SrTiO 3 and the antiferromagnetic Mott insulator NdTiO 3 . As the magnetic field angle is gradually tilted away from the sample normal, the data reveal the interplay between strong k-cubic Rashba-type spin-orbit coupling and a substantial magnetic exchange interaction from local magnetic regions. The resulting quantum corrections to the conduction are in excellent agreement with existing models and allow sensitive determination of the small magnetic moments (22 μ B on average), their magnetic anisotropy, and mutual coupling strength. Furthermore, this effect is expected to arise in other 2D magnetic materials systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Magnetostrictive loss reduction through stress relief annealing in an FeNi-based metal amorphous nanocomposite

FeNi-based metal amorphous nanocomposite alloys are emerging soft magnetic materials with promise for high-speed motor applications. Here we demonstrate a technique to optimize magnetic properties in toroidal cores wound from strain annealed (Fe 70 Ni 30 ) 80 Nb 4 Si 2 B 14 amorphous metal ribbon (AMR). In-line strain annealing (SA) of the AMR yields a strip permeability that monotonically decreases with increasing SA tensions. After winding into toroidal cores, dramatic changes in magnetic properties are observed and determined to be of magnetostrictive origin. A procedure to re-anneal wound toroidal cores to reduce hysteresis and reverse magnetostrictive effects is developed inclusive of casting curvature effects. Here, we investigate re-annealing temperatures between 300 – 470 °C for cores produced from each SA condition. Magnetic core loss, W L , coercivity, H c , squareness ratio, K r , and permeability, µ r , are measured as a function of (stress relief) re-annealing temperature to optimally achieve W 1T,400Hz = 0.51 W/kg, H c = 2.42 A/m, K r = 0.22, and µ r = 35,300.

36 MATERIALS SCIENCE↗

NASA NTRS1992

Eddy current characterization of magnetic treatment of materials

Eddy current impedance measuring methods have been applied to study the effect that magnetically treated materials have on service life extension. Eddy current impedance measurements have been performed on Nickel 200 specimens that have been subjected to many mechanical and magnetic engineering processes: annealing, applied strain, magnetic field, shot peening, and magnetic field after peening. Experimental results have demonstrated a functional relationship between coil impedance, resistance and reactance, and specimens subjected to various engineering processes. It has shown that magnetic treatment does induce changes in a material's electromagnetic properties and does exhibit evidence of stress relief. However, further fundamental studies are necessary for a thorough understanding of the exact mechanism of the magnetic-field processing effect on machine tool service life.

Chern, E. James↗

DOE OSTI2018

Mössbauer Analysis and Cation Distribution of Zn Substituted BaFe{sub 12}O{sub 19} Hexaferrites

Barium hexaferrite is a well-known hard magnetic material. Doping using nonmagnetic cation such as Zn{sup 2+} were found to enhance magnetization owing to preferential tetrahedral site (4 f{sub 1}) occupancy of the zinc. However, the distribution of cations in hexaferrites depends on many factors such as the method of preparation, nature of the cation, and chemical composition. Here, Zn-doped barium hexaferrites (Ba{sub 1−x}Zn{sub x}Fe{sub 12}O{sub 19}) were synthesized by sol-gel method. In this study, we summarized the magnetic properties of Ba{sub 1−x}Zn{sub x}Fe{sub 12}O{sub 19} (x = 0, 0.1, 0.2, 0.3) BaM, investigated by Mössbauer spectroscopy. Moreover, cation distribution was also calculated for all the products. Mössbauer parameters were determined from 57Fe Mössbauer spectroscopy and according to it, the replacement of Ba-Zn affects all parameters such as isomer shift, the variation in line width, hyperfine magnetic field, and quadrupole splitting. Cation distribution revealed the relative area of undoped BaM, 12k, 2a, and 4 f{sub 2} positions which are close to theoretical values.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Scaling study of magnetic phase transition and critical behavior in Nd0.55Sr0.45Mn0.98Ga0.02O3 manganite

Highlights: • The sample of Nd{sub 0.55}Sr{sub 0.45}Mn{sub 0.98}Ga{sub 0.02}O{sub 3} was synthesized via a solid state reaction route. • The PM to FM phase transition of this sample is found to be of second-order. • The critical behaviors and scaling relation for Nd{sub 0.55}Sr{sub 0.45}Mn{sub 0.98}Ga{sub 0.02}O{sub 3} have also been investigated by modified Arrott plot and critical isotherm analysis. • The estimated critical exponents are close to the values for 3D-Ising model. - Abstract: Microscopic magnetic interactions and magnetism can be probed by studying the critical paramagnetic–ferromagnetic phase transition of magnetic materials. In this work, the critical behavior of the lightly Ga-doped manganites Nd{sub 0.55}Sr{sub 0.45}Mn{sub 0.98}Ga{sub 0.02}O{sub 3} (NSMGO) has been investigated. Scaling analysis reveals the critical exponents β = 0.308, γ = 1.197, and δ = 4.916, where their self-consistency and reliability are verified by the Widom scaling law and the scaling equation. These exponents indicate that the magnetic phase transition in NSMGO belongs to the anisotropic 3D-Ising universality class. Nevertheless, the asymptotic critical exponents β{sub eff} and γ{sub eff} are found to approach to the values of 3D-Heisenberg model, implying the existence of isotropic short-range magnetic interactions. We suggest that, although the Nd-based manganites possess a strong magnetocrystalline anisotropy, this effect can be partly averaged out in view of the present polycrystalline NSMGO. Therefore, in the asymptotic critical region, the phase transition reveals the crossover from the scaling of 3D-Ising toward 3D-Heisenberg universality class.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗