Search NASA⌕ Search

SEARCH · Search NASA

Results for “MAGNETIC PROPERTIES”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Faraday effect improvement by Dy{sup 3+}-doping of terbium gallium garnet single crystal

Highly transparent Dy{sup 3+}-doped terbium gallium garnet (TGG) single crystal was grown by Czochralski (Cz) method. Phase composition of the crystal was tested by XRD measurements. The distribution coefficient of Dy{sup 3+} in the crystal was obtained. The optical and magneto-optical properties were analyzed in detail, and magnetic properties of the Dy{sup 3+}-TGG crystal were studied. The paramagnetic behavior is observed down to 10 K. The as-grown crystal exhibited high optical transmittance, particularly in the visible region. The Faraday rotation was investigated over visible and near-infrared regions (VIS–NIR) at room temperature. The Verdet constants increase at measured wavelengths and high thermal stability was found in Dy{sup 3+}-doped TGG, as compared to the properties of pure TGG, indicating that Dy{sup 3+}-doped crystals are preferable for magneto-active materials used in Faraday devices at VIS–NIR wavelengths. - Graphical abstract: Highly transparent Dy{sup 3+}-doped terbium gallium garnet (TGG) and pure TGG single crystals were grown by Czochralski method. The Dy{sup 3+}-doped TGG possesses 20–30% higher Verdet values in reference to TGG independently on wavelength.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Cr3 Triangles induced competing magnetic interactions in the new metal boride TiCrIr2B2: An NMR and DFT study

Highlights: • One-dimensional trigonal arrangements of chromium atoms (Cr{sub 3}) was found in TiCrIr{sub 2}B{sub 2}. • Competing weak ferromagnetic and strong antiferromagnetic interactions support an itinerant d-band character for TiCrIr{sub 2}B{sub 2}. • Spin-polarized and non-spin-polarized DOS results for TiCrIr{sub 2}B{sub 2} unveil an electronic instability and the presence of a pseudogap at E{sub F}, respectively. - Abstract: The presence of one-dimensional trigonal arrangements of chromium atoms (Cr{sub 3}) in the structure of TiCrIr{sub 2}B{sub 2} leads to a magnetic transition near ambient temperature. Herein we report an investigation of the nature of electronic and magnetic properties of TiCrIr{sub 2}B{sub 2} via ab initio calculations together with {sup 11}B NMR Knight shift (K) and spin-lattice relaxation rate (1/T{sub 1}) analysis. The presence of a characteristic rectangular powder pattern below 280 K, absence of a Korringa relation, strong enhancement of 1/T{sub 1}.T at low temperatures and weak temperature dependence of K indicate competition between antiferromagnetic and ferromagnetic spin fluctuations in the itinerant d-band electrons, in agreement with ab initio calculations. One-dimensional trigonal arrangements of magnetically active elements in intermetallic compounds, as is found in TiCrIr{sub 2}B{sub 2}, are quite rare and could lead to exotic phenomena such as spin-chirality and quantum criticality in low-dimensional frustrated lattices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structural, Magnetic, and Thermodynamic Properties of Ordered and Disordered Cobaltite Gd{sub 0.1}Sr{sub 0.9}CoO{sub 3 – δ}

The effect of cationic and anionic orderings on the crystal structure and magnetic properties of substituted rare-earth cobaltites Gd{sub 0.1}Sr{sub 0.9}CoO{sub 3 – δ} was studied using X-ray diffraction, measurement of XANES spectra, and magnetic and thermodynamic characteristics. The effects of ordering cause a decrease in symmetry to tetragonal and a distortion of the coordination octahedra of CoO{sub 6}. Anomalous magnetic and thermodynamic quantities are observed at 260 and 360 K, respectively, for disordered and ordered samples. The XANES spectra measured at the CoK edge did not reveal a noticeable shift in the absorption edge compared with the spectrum of original GdCoO{sub 3}. This suggests that the charge compensation process is associated not only with a change in the electronic state of cobalt ions, but also with the emergence of holes in the 2p states of oxygen.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Electromagnetic wave absorption of multifunctional cementitious composites incorporating polyvinyl alcohol (PVA) fibers and fly ash: Effects of microstructure and hydration

Highlights: • The cementitious composite shows excellent wide-band electromagnetic wave absorption in a frequency range of 2–18 GHz. • The PVA fibers and the fly ash change the dielectric properties of the cementitious composite by Debye polarization. • The iron oxide of the cementitious binders contributes to the magnetic properties of the composites. • The impacts of the microstructure and the hydration of the cementitious composite on its microwave absorption are analyzed. This paper devises a novel method for the adjustment of the pore structure and the hydration of cement to improve the electromagnetic wave absorption of the cementitious composites incorporating polyvinyl alcohol (PVA) fibers and fly ash in a frequency range of 2–18 GHz. The underlying mechanism of the absorption is investigated to explore the possibility of the structural and functional integration of these composites. The electromagnetic parameters of the prepared cementitious composites and those of the raw materials are analyzed in a frequency range of 0.5–18 GHz. Moreover, the pore structure and the chemical environment of the cementitious composites are examined by mercury intrusion porosimetry (MIP), back-scattered electron detector (BSE), and X-ray photoelectron spectroscopy (XPS). The results indicate that the PVA fibers and the high-volume fly ash have a positive effect on electromagnetic wave absorption of the cementitious composites through the adjustment of their pore structure and hydration.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Anion ordering, magnetic structure and properties of the vacancy ordered perovskite Ba{sub 3}Fe{sub 3}O{sub 7}F

This article describes a detailed investigation of the crystallographic and magnetic structure of perovskite type Ba{sub 3}Fe{sub 3}O{sub 7}F by a combined analysis of X-ray and neutron powder diffraction data. Complete ordering of vacancies within the perovskite lattice could be confirmed. In addition, the structure of the anion sublattice was studied by means of the valence bond method, which suggested partial ordering of the fluoride ions on two of the six crystallographically different anion sites. Moreover, the compound was found to show G-type antiferromagnetic ordering of Fe moments, in agreement with magnetometric measurements as well as previously recorded {sup 57}Fe Mössbauer spectroscopy data. - Graphical abstract: The vacancy and anion ordered structure of Ba{sub 3}Fe{sub 3}O{sub 7}F is described together with its magnetic properties. - Highlights: • Ba{sub 3}Fe{sub 3}O{sub 7}F possesses a unique vacancy order not found for other perovskite type compounds. • The valence bond method was used to locate oxide and fluoride ions. • Fluoride ions are distributed only on two of the six anion sites in Ba{sub 3}Fe{sub 3}O{sub 7}F. • The compound shows G-type antiferromagnetic ordering of magnetic moments. • The magnetic structure could be refined in one of the maximal magnetic subgroups of the nuclear structure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

RGO/BaFe12O19/Fe3O4 nanocomposite as microwave absorbent with lamellar structures and improved polarization interfaces

Highlights: • RGO/BaFe{sub 12}O{sub 19}/Fe{sub 3}O{sub 4} nanocomposite are prepared via a two-step solvothermal method. • The maximum reflection loss can reach −46.04 dB, and the effective absorption bandwidth under −10 dB is 5.68 GHz. • Interfacial polarization as one of the mechanism for the enhanced absorption properties was detailedly analyzed. - Abstract: In this paper, we designed and prepared a composite of BaFe{sub 12}O{sub 19} (BFO) flakes, two-dimensional graphene and Fe{sub 3}O{sub 4} nanoparticles using a two-step solvothermal method. The combination of BFO flakes and two-dimensional graphene could effectively enhance the heterointerface and is believed to be favorable to enhance the interface polarization. The introduction of inverse spinel Fe{sub 3}O{sub 4} as the third phase could increase the saturated magnetization. The phase structure, morphology, magnetic properties and electromagnetic wave absorption performance of the as-prepared samples were characterized. Due to the enhanced interfacial polarization between the BaFe{sub 12}O{sub 19} flakes and graphene, the composite of RGO/BaFe{sub 12}O{sub 19}/Fe{sub 3}O{sub 4} exhibits excellent microwave absorption properties. The maximum reflection loss can reach -46.04 dB at 15.6 GHz with a thickness of 1.8 mm, and the effective absorption bandwidth reaches 5.68 GHz (from 11.60 GHz to 17.28 GHz). It is believed that the RGO/BaFe{sub 12}O{sub 19}/Fe{sub 3}O{sub 4} composites can find potential application in the field of microwave absorption due to their excellent absorption properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Magnetic field induced insulator-metal transition in nanocrystalline Pr{sub 0.67}Ca{sub 0.33}MnO{sub 3} compounds: Evidence of large temperature co-efficient of resistance

We report the electronic transport, magneto-transport, and magnetic properties of nanocrystalline Pr{sub 0.67}Ca{sub 0.33}MnO{sub 3} compound. A magnetic field induced insulator—metal transition appears for the external magnetic field higher than 50 kOe. We have obtained large value of the temperature coefficient of resistance (TCR) along with magnetoresistance and field coefficient of resistance (FCR). The value of TCR is 135%/K at 48 K. The calculated magnetoresistance is about −9.8 × 10{sup 7}% for 70 kOe and maximum FCR is about 320%/kOe around 75 K. Due to the application of the external magnetic field, charge ordered state of the compound is destabilized leading to such large values of TCR and FCR. Large values of TCR and FCR along with the large magnetoresistance exhibited by the material is interesting from the application point of view.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Effect of Oxygen on the Quantum, Magnetic, and Thermodynamic Properties of Co Nanowires on the Reconstructed Anisotropic (1 × 2)/Au(110) and (1 × 2)/Pt(110) Surfaces: Ab Initio Approach

Ab initio theoretical study of the quantum magnetic properties of Co nanowires on the pure and oxygen-reconstructed (1 × 2)/Au(110) and (1 × 2)/Pt(110) surfaces is performed. Their structures and electronic configurations are calculated using the electron density functional theory. High values of magnetic moment and magnetic anisotropy energies of Co atoms are found on both pure and oxygen-reconstructed (1 × 2)/Au(110) and (1 × 2)/Pt(110) surfaces. The adsorption of oxygen atoms on the (1 × 2)/Au(110) substrate is shown to affect the structural arrangement of Co nanowire atoms on this substrate and to increase the magnetic anisotropy energy (by 1.91 meV per nanowire atom). The adsorption of oxygen on the Pt(110) substrate substantially decreases the magnetic anisotropy energy of the Co nanowire on it (by 5.98 meV per atom). The origin of these changes is revealed by analyzing the local densities of states of the d electrons of nanowire atoms. The temperature ranges of the states with the lowest free surface energy are determined using the atomistic thermodynamics methods. These data and the available experimental data are used to predict the possibility of observing the structures under study in experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Electronic Properties and Magnetocaloric Effect of GdNi{sub 4}Si: Ab Initio Calculations, Mean Field Approximation, and Monte Carlo Simulation

We investigated the magnetic properties and magnetocaloric effect of GdNi{sub 4}Si by using a combination of first-principle density functional theory (DFT) calculations and Monte Carlo Simulation. Ab initio calculations show the stability of the ferromagnetic phase in this material. The Monte Carlo simulations combined with ab initio exchange coupling constants as input parameters lead to discuss the transition temperature, critical exponents, and isothermal entropy changes. The measured critical temperature and the isothermal magnetic entropy changes for a field change of 14T in good agreement with the experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Magnetic and electrode properties, structure and phase relations of the layered triangular-lattice tellurate Li{sub 4}NiTeO{sub 6}

We examined the magnetic properties of layered oxide Li{sub 4}NiTeO{sub 6} by magnetic susceptibility, magnetization and ESR measurements and density functional calculations, and characterized phase relations, crystal structure and electrochemical properties of Li{sub 4}NiTeO{sub 6}. The magnetization and ESR data indicate the absence of a long-range magnetic order down to 1.8 K, and the magnetic susceptibility data the presence of dominant antiferromagnetic interactions. These observations are well accounted for by density functional calculations, which show that the spin exchanges of the LiNiTeO{sub 6} layers in Li{sub 4}NiTeO{sub 6} are strongly spin frustrated. The electrochemical charging of Li{sub 4}NiTeO{sub 6} takes place at constant potential of ca. 4.2 V vs. Li/Li{sup +} indicating two-phase process as confirmed by X-rays. The starting phase is only partially recovered on discharge due to side reactions. - Graphical abstract: No long-range magnetic order due to frustration in 2D triangular lattice antiferromagnet Li{sub 4}NiTeO{sub 6}. - Highlights: • Li{sub 4}NiTeO{sub 6} is 2D triangular lattice magnet with no long-range order down to 1.8 K. • Intralayer exchange interactions are antiferromagnetic and strongly spin frustrated. • The electrochemical Li extraction proceeds in a two-phase mode at 4.2 V vs. Li/Li{sup +}. • The electrochemical charge–discharge is only partially reversible. • Li{sub 2}O–NiO{sub y}–TeO{sub x} phase relations are reported; Li{sub 4}NiTeO{sub 6} is essentially stoichiometric.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Electronic conduction mechanism for NFO/(Pb{sub 0.80}Sr{sub 0.20}) TiO{sub 3} bi-layered nanostructure multiferroic composite thin film

Multiferroic 2-2 type bi-layered NFO/(Pb{sub 0.80}Sr{sub 0.20}) TiO{sub 3} composite thin film on Pt/TiO{sub 2}/Si substrate was prepared by novel metallo-Organic process using spin coating technique. The structural and surface morphology were confirmed by X-Ray diffraction (XRD) atomic force microscope (AFM). Significantly improved ferroelectric properties (P{sub s} ~ 17.25, P{sub r} ~ 8.02 µC/cm{sup 2} and E{sub c} ~ 404 kV/cm) and magnetic properties (M{sub s} ~ 117 emu/cc, M{sub r} ~ 0.83 emu/cc and H{sub c} ~ 20 Oe) were observed at room temperature. The leakage current densities in NFO/PST composites film have been studied. Poole–Frankel bulk limited conduction mechanism dominates of film at relatively high electric filed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

High energy ball milling study of Fe{sub 2}MnSn Heusler alloy

The structural and magnetic properties of as-melted and high energy ball milled alloy samples have been studied by X-ray diffraction, DC magnetization and electronic structure calculations by means of density functional theory. The observed properties are compared to that of the bulk sample. There is a very good enhancement of saturation magnetization and coercivity in the nano-sized samples as compared to bulk which is explained in terms of structural disordering and size effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Room temperature neutron diffraction and magnetic studies of multiferroic Pb{sub 0.9}Bi{sub 0.1}Fe{sub 0.55}Nb{sub 0.45}O{sub 3} solid solution

The Pb{sub 0.9}Bi{sub 0.1}Fe{sub 0.55}Nb{sub 0.45}O{sub 3} (PBFNO) solid solution was synthesized by single step solid state reaction method and the optimized parameters are 700°C for 2hr (calcination) and 800°C for 3hr (sintering). The formation of desired material was confirmed using X-Ray Diffraction (XRD) and Neutron Diffraction (ND) studies. The structural and magnetic properties of the sintered pellets were investigated at room temperature (RT) through XRD, ND and Magnetic (M-H) studies. The structural analysis was carried out by Rietveld refinement through the Full Prof program. Rietveld refined XRD and ND patterns confirms the monoclinic structure with Cm space group and obtained cell parameters from the ND data are a = 5.651(2) Å, b = 5.658(2) Å, c = 4.005(1) Å and α = 90°, β = 89.98(1)°, γ = 90°. RT M-H curve studies have been carried out. It shows the clear opening of hysteresis (M–H) loop, is evidenced as the existence of weak ferromagnetism at RT. The M-H data shows existence weak ferromagnetism embedded in an antiferromagnetic matrix structure. The dielectric constant with frequency shows the formation of barrier layers at the grain and grain boundary interfaces gives rise to interfacial space charge polarization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Direct-write 3D printing of NdFeB bonded magnets

We report a method to fabricate Nd-Fe-B bonded magnets of complex shape via extrusion-based additive manufacturing (AM), also known as 3D-printing. We have successfully formulated a 3D-printable epoxy-based ink for direct-write AM with anisotropic MQA NdFeB magnet particles that can be deposited at room temperature. The new feedstocks contain up to 40 vol.% MQA anisotropic Nd-Fe-B magnet particles, and they are shown to remain uniformly dispersed in the thermoset matrix throughout the deposition process. Ring, bar, and horseshoe-type 3D magnet structures were printed and cured in air at 100°C without degrading the magnetic properties. Lastly, this study provides a new pathway for fabricating Nd-Fe-B bonded magnets with complex geometry at low temperature, and presents new opportunities for fabricating multifunctional hybrid structures and devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Robust Half-Metallicity in Quaternary Heusler Compounds KSrNZ (Z = O, S, and Se)

The first principle calculations based on density functional theory using full potential linearized augmented plane wave method was performed on the quaternary Heusler alloys KSrNZ (Z = O, S, and Se). Studies on structural properties showed that quaternary Heusler alloys KSrNZ (Z = O, S, and Se) were stable in Y{sub I}-type structure. Furthermore, values of formation energies confirmed that these alloys may be synthesized experimentally. Verification of electronic properties resulted that KSrNO, KSrNS, and KSrNSe compounds were half-metals at equilibrium lattice constants with majority band gaps of 4.61, 3.82, and 3.51 eV, respectively. KSrNZ (Z = O, S, and Se) compounds maintained half-metallic behavior in relatively wide ranges of lattice constant under uniform strain distortion. This indicates that these compounds are promising materials for future spintronic applications. Furthermore, the origin of half-metallic characteristic was verified using electronic density of states. Calculations of magnetic properties showed that the total magnetic moments of KSrNZ (Z = O, S, and Se) were obtained equal to 2 μ{sub B} satisfying the famous Slater-Pauling rule (M{sub tot}= 12-Z{sub tot}).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic and Structural Properties of SrFe{sub 12−x}Cr{sub x}O{sub 19} (x = 0, 0.25, 0.5, 0.75, 1) Hexaferrite Powders Obtained by Sol–Gel Auto-Combustion Method

The crystalline structure and magnetic properties of chromium substituted hexagonal strontium ferrite, SrFe{sub 12−x}Cr{sub x}O{sub 19} (x = 0, 0.25, 0.5, 0.75, 1), nanoparticles have been investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometer (VSM). These materials were prepared by the chemical sol–gel auto-combustion method. From the structural analysis, it was observed that the non-magnetic phase α-Fe{sub 2}O{sub 3} appears after x ≥ 0.5 and remains to be a hexagonal magnetoplumbite phase for x < 0.5. Various parameters such as lattice constants (a and c) were calculated from the XRD data. The coercively H{sub c} initially decreases and then increases with increasing chromium concentration. The saturation magnetization exhibits an increase as the chromium content increases up to (x = 0.25) and then decreases with increase in the Cr content ion from 75.19 to 61.66 emu/g due to the substitution of Fe{sup 3+} ions by less magnetic Cr{sup 3+} ions. Furthermore, M{sub r} continually decreases with increase in the Cr content.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Magnetic and electronic properties of porphyrin-based molecular nanowires

Using spin-polarized density functional theory calculations, we performed theoretical investigations on the electronic and magnetic properties of transition metal embedded porphyrin-based nanowires (TM-PNWs, TM = Cr, Mn, Co, Ni, Cu, and Zn). Our results indicate that Ni-PNW and Zn-PNW are nonmagnetic while the rest species are magnetic, and the magnetic moments in TM-PNWs and their corresponding isolated monomer structures are found to be the same. In addition, the spin coupling in the magnetic nanowires can be ignored leading to their degenerate AFM and FM states. These results can be ascribed to the weak intermetallic interactions because of the relatively large distances between neighbor TM atoms. Among all TM-PNW structures considered here, only Mn-PNW shows a half-metallic property while the others are predicted to be semiconducting. The present work paves a new way of obtaining ferromagnetic porphyrin-based nanowires with TM atoms distributed separately and orderly, which are expected to be good candidates for catalysts, energy storage and molecular spintronics.

36 MATERIALS SCIENCE↗