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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 1,621 records · Page 90
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

X-ray spectroscopies studies of the 3d transition metal oxides and applications of photocatalysis

Some recent advances in synchrotron based x-ray spectroscopy enable materials scientists to emanate fingerprints on important materials properties, e.g., electronic, optical, structural, and magnetic properties, in real-time and under nearly real-world conditions. This characterization, then, in combination with optimized materials synthesis routes and tailored morphological properties could contribute greatly to the advances in solid-state electronics and renewable energy technologies. In connection to this, such perspective reflects the current materials research in the space of emerging energy technologies, namely photocatalysis, with a focus on transition metal oxides, mainly on the Fe 2 O 3 - and TiO 2 -based materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Sub-tesla On-Chip Nanomagnetic Metamaterial Platform for Angle-Resolved Photoemission Spectroscopy

Magnetically controlled states in quantum materials are central to their unique electronic and magnetic properties. However, direct momentum-resolved visualization of these states via angle-resolved photoemission spectroscopy (ARPES) has been hindered by the disruptive effect of magnetic fields on photoelectron trajectories. Here, we introduce an in situ method that is, in principle, capable of applying magnetic fields up to 1 T. This method uses substrates composed of nanomagnetic metamaterial arrays with alternating polarity. Such substrates can generate strong, homogeneous, and spatially confined fields applicable to samples with thicknesses up to the micron scale, enabling ARPES measurements under magnetic fields with minimal photoelectron trajectory distortion. Here, we demonstrate this minimal distortion with ARPES data taken on monolayer graphene. Our method paves the way for probing magnetic field-dependent electronic structures and studying field-tunable quantum phases with state-of-the-art energy-momentum resolutions.

Magnetic properties↗
DOE OSTI2016

Intrinsic magnetism of monolayer graphene oxide quantum dots

Monolayer graphene oxide quantum dots (GOQDs) were obtained by oxidative cutting. The magnetic properties of GOQDs were studied. The results show that most of GOQDs are nonmagnetic, and only few of GOQDs are weakly paramagnetic. The ratio of magnetic GOQDs with the average diameter of 4.13, 3.3, and 1.67 nm is 1/14, 1/15, and 1/70, respectively. It is proposed that the edge states magnetism is suppressed by the edge defects and/or the magnetic correlation induced spins cancellation between magnetic fragments of the boundary, and hydroxyl groups on the basal plane are the major magnetic source of magnetic GOQDs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Structural and electronic properties of Li-ion battery cathode material MoF{sub 3} from first-principles

The transition metal fluorides have been extensively investigated recently as the electrode materials with high working voltage and large capacity. The structural, electronic and magnetic properties of MoF{sub 3} are studied by the first-principles calculations within both the generalized gradient approximation (GGA) and GGA+U frameworks. Our results show that the antiferromagnetic configuration of MoF{sub 3} is more stable than the ferromagnetic one, which is consistent with experimental results. The analysis of the electronic density of states shows that MoF{sub 3} is a Mott–Hubbard insulator with a d–d type band gap, which is similar to the case of FeF{sub 3}. Moreover, small spin polarizations were found on the sites of fluorine ions, which accords with a fluorine-mediated superexchange mechanism for the Mo–Mo magnetic interaction. - Graphical abstract: Deformation charge density and spin-density for MoF{sub 3} in the AF configuration. - Highlights: • The ground state of MoF{sub 3} is shown to be antiferromagnetic, in consistent with experiments. • The electronic states show that MoF{sub 3} is a Mott–Hubbard insulator with a d–d type band gap. • A fluorine-mediated super-exchange mechanism for the Mo–Mo magnetic interaction is shown.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Critical Behavior and Size Dependence of Magnetic Entropy Changes on La{sub 0.6}Sr{sub 0.4}MnO{sub 3} Manganite

In this work, nano and micro scales of La{sub 0.6}Sr{sub 0.4}MnO{sub 3} ceramics are prepared by sol-gel and solid-state reaction methods. In order to investigate the dependency of the magnetic properties on the size variation of as-prepared samples, their magnetic entropy change (ΔS{sub M}) at different magnetic fields and temperatures are fitted by Lorentz universal function. The obtained results confirmed the size impression on magneto-caloric properties, in spite of proving significant influence on some parameters related to the refrigeration system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

The modification of the structure of multilayer Co/Pt films by the irradiation with a focused helium ion beam

We report here on the possibility of a local modification of Co/Pt multilayered magnetic films by focused ion beam irradiation. The changes of structural and magnetic properties are experimentally investigated as a function of irradiation fluence. The method is used to form lateral structures with the periods up to 100 nm. The magnetic force microscopy accompanied by Hall effect measurements of the structure indicate the formation of magnetic skyrmion lattices in the absence of Dzyaloshinskii-Moriya interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Preparation and Characterization of Mn Doped ZnO Nanorods

Mn doped ZnO nanorods were prepared by chemical precipitation method. The micro-structural and structural properties of the nanorods were calculated from the X-ray diffraction technique. The formed nanorods was seen in the scanning electron microscopy. The purity of the sample was confirmed by the energy dispersive X-ray analysis (EDX). The optical properties were studied using UV-Vis spectroscopy and photoluminescence. In the photoluminescence spectrum, the peaks due to recombination of free electrons, oxygen vacancy and intrinsic defects were observed. The magnetic properties were studied using vibrating sample magnetometer (VSM) and the paramagnetic nature of the material was confirmed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Electric field controlled spin interference in a system with Rashba spin-orbit coupling

There have been intense research efforts over the last years focused on understanding the Rashba spin-orbit coupling effect from the perspective of possible spintronics applications. An important component of this line of research is aimed at control and manipulation of electron’s spin degrees of freedom in semiconductor quantum dot devices. A promising way to achieve this goal is to make use of the tunable Rashba effect that relies on the spin-orbit interaction in a two-dimensional electron system embedded in a host semiconducting material that lacks inversion-symmetry. This way, the Rashba spin-orbit coupling effect may potentially lead to fabrication of a new generation of spintronic devices where control of spin, thus magnetic properties, is achieved via an electric field and not a magnetic field. In this work we investigate theoretically the electron’s spin interference and accumulation process in a Rashba spin-orbit coupled system consisting of a pair of two-dimensional semiconductor quantum dots connected to each other via two conducting semi-circular channels. The strength of the confinement energy on the quantum dots is tuned by gate potentials that allow “leakage” of electrons from one dot to another. While going through the conducting channels, the electrons are spin-orbit coupled to a microscopically generated electric field applied perpendicular to the two-dimensional system. We show that interference of spin wave functions of electrons travelling through the two channels gives rise to interference/conductance patterns that lead to the observation of the geometric Berry’s phase. Achieving a predictable and measurable observation of Berry’s phase allows one to control the spin dynamics of the electrons. It is demonstrated that this system allows use of a microscopically generated electric field to control Berry’s phase, thus, enables one to tune the spin-dependent interference pattern and spintronic properties with no need for injection of spin-polarized electrons.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Influence of uniaxial single-ion anisotropy on the magnetic and thermal properties of Heisenberg antiferromagnets within unified molecular field theory

Here, the influence of uniaxial single-ion anisotropy –DS 2 z on the magnetic and thermal properties of Heisenberg antiferromagnets (AFMs) is investigated. The uniaxial anisotropy is treated exactly and the Heisenberg interactions are treated within unified molecular field theory (MFT), where thermodynamic variables are expressed in terms of directly measurable parameters. The properties of collinear AFMs with ordering along the z axis (D>0) in applied field H z = 0 are calculated versus D and temperature T, including the ordered moment μ, the Néel temperature T N , the magnetic entropy, internal energy, heat capacity, and the anisotropic magnetic susceptibilities χ ∥ and χ ⊥ in the paramagnetic (PM) and AFM states. The high-field average magnetization per spin μ z (H z ,D,T) is found, and the critical field H c (D,T) is derived at which the second-order AFM to PM phase transition occurs. The magnetic properties of the spin-flop (SF) phase are calculated, including the zero-field properties T N (D) and μ(D,T). The high-field μ z (H z ,D,T) is determined, together with the associated spin-flop field H SF (D,T) at which a second-order SF to PM phase transition occurs. The free energies of the AFM, SF, and PM phases are derived from which H z –T phase diagrams are constructed. For f J =–1 and –0.75, where f J = θ pJ /T NJ and θ pJ and T NJ are the Weiss temperature in the Curie-Weiss law and the Néel temperature due to exchange interactions alone, respectively, phase diagrams in the H z –T plane similar to previous results are obtained. However, for f J = 0 we find a topologically different phase diagram where a spin-flop bubble with PM and AFM boundaries occurs at finite H z and T. Also calculated are properties arising from a perpendicular magnetic field, including the perpendicular susceptibility χ ⊥ (D,T), the associated effective torque at low fields arising from the –DS 2 z term in the Hamiltonian, the high-field perpendicular magnetization μ ⊥ , and the perpendicular critical field H c⊥ at which the second-order AFM to PM phase transition occurs. In addition to the above results for D > 0, the T N (D) and ordered moment μ(T,D) for collinear AFM ordering along the x axis with D < 0 are determined. In order to compare the properties of the above spin systems with those of noninteracting systems with –DS 2 z uniaxial anisotropy with either sign of D, Supplemental Material is provided in which results for the thermal and magnetic properties of such noninteracting spin systems are given.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Magneto-optical and Photocatalytic Properties of Ferromagnetic Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} (0.0 ≤ y ≤ 1.0) Spinel Nano-ferrites

Spinel Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} (0.0 ≤ y ≤ 1.0) ferrite magnetic nanoparticles (MNPs) were synthesized by a sol-gel combustion method using urea as the reducing agent/fuel. Powder X-ray diffraction (XRD) analysis revealed the formation of cubic spinel Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} powders and confirmed pure crystalline phase and the average crystalline size of 21.25 to 17.04 nm. Functional group bonds between metal and oxygen (M–O) were confirmed by Fourier transform infrared (FT-IR) spectra. The microstructure of the powders was recorded by high-resolution scanning electron microscope (HR-SEM) and confirmed the particle-like surface morphology with smaller agglomeration, due to the magnetic interaction of the particles. Energy-dispersive X-ray (EDX) results showed the composition of the expected elements and confirmed the phase purity of the products. Vibrating sample magnetometer (VSM) technique recorded at room temperature was used to analyse the magnetic properties of the samples and the hysteresis loops showed the ferromagnetic behaviour. Moreover, the samples Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} NPs were tested for the photocatalytic degradation (PCD) of methylene blue (MB) dye and the sample y = 0.6 showed maximum degradation efficiency (96.83 %), due to the smaller particle size with higher surface area than other compositions. Furthermore, spinel Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} nano-photocatalysts can be reused several times without change of its catalytic activity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Paramagnetic Properties of Rare Earth Hydroxides, Oxalates, and Dibutyl Phosphates

Magnetic separations present a promising approach for the recovery of rare earth (RE) elements from mixtures, particularly when coupled with precipitation techniques that enhance process efficiency and selectivity. However, the magnetic properties of RE materials typically encountered in the separations industry are not well characterized. Here, we synthesized a series of RE materials, combining four REs – praseodymium (Pr), neodymium (Nd), terbium (Tb), and dysprosium (Dy) – with three precipitating agents – hydroxide, oxalate, and dibutyl phosphate. All materials showed typical paramagnetic behavior consistent with the Curie-Weiss law. At low temperatures, we observed weak antiferromagnetic correlations, which were more pronounced for the lighter RE ions (Pr, Nd). Particle morphology and crystallography analyses showed that the dibutyl phosphates were well-ordered metal-organic frameworks, the oxalates were crystals with mixed hydration states, and the hydroxides were mostly amorphous. Regardless of the degree of crystallinity, the effective magnetic moments aligned well with theoretical estimates based on Hund's rules and 4f electron configurations of the corresponding RE ions. For a given RE ion, the magnetophoretic response was thus determined by the size of the particles rather than specific metal-ligand coupling, with dibutyl phosphate promoting the formation of larger crystals that were the most strongly attracted to magnets.

Wang, Qingpu (ORCID:0000000156041571)↗
DOE OSTI2018

Superconducting Properties of Indium Nanostructured in Pores of Thin Films of SiO{sub 2} Microspheres

Samples of a superconducting indium nanocomposite based on a thin-film porous dielectric matrix prepared by the Langmuir–Blodgett method are obtained for the first time, and their low-temperature electrophysical and magnetic properties are studied. Films with thickness b ≤ 5 μm were made from silicon dioxide spheres with diameter D = 200 and 250 nm; indium was introduced into the pores of the films from the melt at a pressure of P ≤ 5 kbar. Thus, a three-dimensional weakly ordered structure of indium nanogranules was created in the pores, forming a continuous current-conducting grid. Measurements of the temperature and magnetic field dependences of the resistance and magnetic moment of the samples showed an increase in the critical parameters of the superconductivity state of nanostructured indium (critical temperature T{sub c} ≤ 3.62 K and critical magnetic field H{sub c} at T = 0 K H{sub c}(0) ≤ 1700 Oe) with respect to the massive material (T{sub c} = 3.41 K, H{sub c}(0) = 280 Oe). In the dependence of the resistance on temperature and the magnetic field, a step transition to the superconductivity state associated with the nanocomposite structure was observed. A pronounced hysteresis M(H) is observed in the dependence of the magnetic moment M of the nanocomposite on the magnetic field at T < T{sub c}, caused by the multiply connected structure of the current-conducting indium grid. The results obtained are interpreted taking into account the dimensional dependence of the superconducting characteristics of the nanocomposite.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Monte Carlo Study of the Core-Shell Phase Transitions in Nanostructure Systems

We present in this work the effects of the external magnetic field, the exchange anisotropy, the coupling exchange interaction and the temperature on the magnetic properties of the nanostructure systems. More exactly, the effect of the core-shell spin Ising systems has been also examined. A number of favorable phenomena such as the wetting magnetic and the layering transitions have been investigated. The Monte Carlo simulations have been used to investigate the behavior of these nanostructure systems and to obtain the interesting results presented in the form of the phase diagrams.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effects of molybdenum doping and thermal annealing on the physical properties of amorphous In–Zn–O films

Highlights: • The effects of Mo doping and thermal annealing on a-IZO films were studied. • The carrier mobility of Mo-doped a-IZO films was enhanced by thermal annealing. • The optical bandgap of a-IZO films was unaffected by Mo doping. • Ferromagnetism was observed in Mo-doped a-IZO films after annealing. - Abstract: Amorphous In–Zn–O (a-IZO) films doped with Mo were prepared on glass substrates by using magnetron co-sputtering technique. The Mo concentration was controlled by varying the sputtering power applied on the Mo target. The effects of Mo doping and thermal annealing on the electrical, optical and magnetic properties of the a-IZO films were studied. The electrical properties of a-IZO films were found to be strongly affected by Mo doping and thermal annealing. The optical transmission near the absorption edge of a-IZO films is enhanced by Mo doping due to the decrease in reflection. The optical bandgap estimated to be 3.2 eV of a-IZO films is unaffected by Mo doping and thermal annealing. Moreover, some of Mo-doped films exhibit room-temperature ferromagnetism after annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Iron oxide and gold nanoparticles in cancer therapy

Continuous research activities in the field of nanomedicine in the past decade have, to a great extent, been focused on nanoparticle technologies for cancer therapy. Gold and iron oxide nanoparticles (NP) are two of the most studied inorganic nanomaterials due to their unique optical and magnetic properties. Both types of NPs are emerging as promising systems for anti-tumor drug delivery and for nanoparticle-mediated thermal therapy of cancer. In thermal therapy, localized heating inside tumors or in proximity of tumor cells can be induced, for example, with Au NPs by radiofrequency ablation heating or conversion of photon energy (photothermal therapy) and in iron oxide magnetic NPs by heat generation through relaxation in an alternating magnetic field (magnetic hyperthermia). Furthermore, the superparamagnetic properties of iron oxide nanoparticles have led to their use as potent MRI (magnetic resonance imaging) contrast agents. Surface modification/coating can produce NPs with tailored and desired properties, such as enhanced blood circulation time, stability, biocompatibility and water solubility. To target nanoparticles to specific tumor cells, NPs should be conjugated with targeting moieties on the surface which bind to receptors or other molecular structures on the cell surface. The article presents several approaches to enhancing the specificity of Au and iron oxide nanoparticles for tumor tissue by appropriate surface modification/functionalization, as well as the effect of these treatments on the saturation magnetization value of iron oxide NPs. The use of other nanoparticles and nanostructures in cancer treatment is also briefly reviewed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Switching of Coercivity Process in MnBi Alloys

MnBi-based alloys represent an interesting choice for developing rare earth-free permanent magnets due to the high magnetocrystalline anisotropy of their characteristic low-temperature intermetallic phase (LTIP) with hexagonal structure. In this work, we discuss the switching of coercivity mechanism in MnBi alloys by modulation of their phase distribution and microstructure. As-cast MnBi alloys obtained by suction-casting technique exhibited LTIP interspersed within Bi- and Mn-rich areas. A noticeable coercivity field of 282 kA/m was observed. The coercivity mechanism for this alloy was explained in terms of the nucleation of reverse domains after saturation, by means of the Kronmüller equation, which incorporates the detrimental effect of microstructure defects through fitting parameters associated to reduced intrinsic magnetic properties at grain size boundaries, interfaces, and local demagnetizing fields. Subsequent annealing at 583 K for 24 h produced a marked reduction of coercivity (down to 16 kA/m), reflecting a switching of coercivity process from nucleation to pinning of domain walls. The key microstructural feature determining this variation is the formation/suppression of Bi-rich areas, which promotes the nucleation and growth of the initial MnBi intermetallic phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Fabrication of highly dense isotropic Nd-Fe-B nylon bonded magnets via extrusion-based additive manufacturing [Fabrication of highly dense isotropic Nd-Fe-B bonded magnets via extrusion-based additive manufacturing]

Magnetically isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts. The density of the printed magnet is ~5.2 g/cm 3 . The room temperature magnetic properties are: intrinsic coercivity H ci = 8.9 kOe (708.2 kA/m), remanence B r = 5.8 kG (0.58 T), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m 3 ). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability as revealed by flux aging loss measurements. Tensile tests performed at 25 °C and 100 °C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely low eddy current loss and high resistivity. Lastly, we demonstrate the performance of the 3D printed magnets in a DC motor configuration via back electromotive force measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ultrafast optical control of surface and bulk magnetism in magnetic topological insulator/antiferromagnet heterostructure

Abstract Optical control of the magnetic properties in topological insulator systems is an important step in applying these materials in ultrafast optoelectronic and spintronic schemes. In this work, we report the experimental observation of photo-induced magnetization dynamics in the magnetically doped topological insulator (MTI)/antiferromagnet (AFM) heterostructure composed of Cr-(Bi,Sb) 2 Te 3 /CrSb. Through proximity coupling to the AFM layer, the MTI displays a dramatically enhanced magnetism, with robust perpendicular magnetic anisotropy. When subjected to intense laser irradiation, both surface and bulk magnetism of the MTI are weakened by laser-induced heating of the lattice, however, at the surface, the deleterious heat effect is compensated by the strengthening of Dirac-hole-mediated exchange coupling as demonstrated by an unconventional pump-fluence-dependent exchange-bias effect. Through theoretical analyses, the sizes of exchange coupling energies are estimated in the MTI/AFM bilayer structure. The fundamentally different mechanisms supporting the surface and bulk magnetic order in MTIs allow a novel and distinctive photo-induced transient magnetic state with antiparallel spin configuration, which broadens the understanding of the magnetization dynamics of MTIs under ultrashort and intense optical excitation.

42 ENGINEERING↗