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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Electrical, optical, and magnetic properties of amorphous yttrium iron oxide thin films and consequences for non-local resistance measurements

We present magnetic characterization, charge resistivity, and optical photoluminescence measurements on amorphous yttrium iron oxide thin films ( ⁠a-Y–Fe–O), with supporting comparisons to amorphous germanium (⁠ a-Ge) films. We measured magnetic properties with both SQUID magnetometry and polarized neutron reflectometry. These results not only confirm that a-Y–Fe–O is a disordered magnetic material with strong predominantly antiferromagnetic exchange interactions and a high degree of frustration, but also that it is best understood electrically as a disordered semiconductor. As with amorphous germanium, a-Y–Fe–O obeys expectations for variable-range hopping through localized electron states over a wide range of temperature. We also clarify the consequences of charge transport through such a semiconducting medium for non-local voltage measurements intended to probe spin transport in nominally insulating magnetic materials. We further compare non-local resistance measurements made with “quasi-dc” automated current reversal to ac measurements made with a lock-in amplifier. These show that the “quasi-dc” measurement has an effective ac current excitation with frequency up to approximately 22 Hz, and that this effective ac excitation can cause artifacts in these measurements including incorrect sign of the non-local resistance. Here, this comprehensive investigation of non-local resistance measurements in a-Y–Fe–O shows no evidence of spin transport on micrometer length scales, which is contrary to our original work, and in line with more recent investigations by other groups.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Martensitic Transformation and Magnetic Properties of the CuAl, CuAlMn, and CuAlMnZn Alloys

In the present work, the effect of alloying elements on the phase transformation which are formed by cooling effect in CuAl, CuAlMn, and CuAlMnZn (wt%) alloys are investigated using scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) characterization techniques. From SEM observations, the martensite formation with different morphologies is observed in these alloys. But the results of the scanning electron microscope investigations presented in this work have not formed the precipitates in the CuAl alloy with Mn or Zn additions. We found that magnetic saturation and coercivity values decreased with the addition of Mn and Zn elements to the CuAl alloy. The findings confirmed the variation in magnetic properties, which occurred in the result of adding different alloying elements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effects of Mg Substitution on the Structural and Magnetic Properties of Ni{sub 0.2}Mg{sub x}Co{sub 0.8−x}Fe{sub 2}O{sub 4} Nanoparticle Ferrites

Sol-gel auto-combustion is a method of preparing ferrite by combining combustion with chemical gel. In this study, Ni-Mg-Co ferrite powders are prepared by coprecipitation method, and the nanocrystals of Ni{sub 0.2}Mg{sub x}Co{sub 0.8−x}Fe{sub 2}O{sub 4} are successfully synthesized. The structure and magnetic properties of undoped and Mg-substituted Ni-Co ferrite nanoparticles are systematically investigated. The methods used to characterize the prepared samples are X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), and Vibrating sample magnetometry (VSM). The synthesized samples are confirmed by XRD analysis to form a single-phase cubic spinel structure with crystals between 48 and 50 nm. With the increase of Mg ion concentration, the lattice constant decreases. The results of FTIR spectroscopy indicated that a spinel structure was formed. Transmission electron microscopy (TEM) images show spherical cubic microcrystals in the samples. EDX analysis confirms that the synthesized ferrite is pure phase structure, and Mg{sup 2+} is successfully replaced. With the increase of Mg{sup 2+} ion content, the saturation magnetization and remanent magnetization decreased from 70.16 to 39.77 emu/g and 36.40 to 20.20 emu/g at room temperature, respectively. Meanwhile, the coercivity decreases from 1032.16 to 378.50 Oe by increasing Mg{sup 2+} concentration. This also indicates that the Mg-substituted Ni-Co nano-ferrite has a low magnetic of multi-ferric material. The increasing of peak height of dM/dH at H{sub m} indicates that the cubic spinel structure sample has good crystallinity and magnetic stability.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Ab Initio Investigation of Structural, Electronic, and Magnetic Properties of Cr-Doped ZnS and ZnSe in Wurtzite Structure

Using the first-principles calculations with the full potential linear muffin–tin orbital (FP-LMTO) method, we investigated the structural, electronic, and magnetic properties of Zn{sub 1−x}Cr{sub x}(S,Se)-diluted magnetic semiconductors (DMSs) in wurtzite structures with varying concentrations (x = 0.0625, x = 0.125, and x = 0.25) of Cr. The electronic properties indicated that Zn{sub 1−x}Cr{sub x}(S,Se), in all concentrations, exhibited half-metallic ferromagnetic (HMF) behavior with spin polarization of 100%. The density of states showed a hybridization between the p(S, Se) and 3d(Cr) states, which created an antibonding state in the gap that stabilized the ferromagnetic ground state linked to the double-exchange mechanism. Therefore, these compounds are highly likely candidates for spintronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Properties of Co-doped Bismuth Oxide (δ-Bi{sub 2}O{sub 3}) at Low Temperature

The (Bi{sub 2}O{sub 3}){sub 1−x−y}(Gd{sub 2}O{sub 3}){sub x}(Lu{sub 2}O{sub 3}){sub y} material compounds were prepared by using the solid-state reaction technique under normal air conditions. The heat treatments of the ternary samples were performed firstly at 800 °C for 48 h and then at 750 °C for 100 h. The structural, morphological, and magnetic properties of the materials were characterized by X-ray powder diffraction (XRD), scanning electron microscope, and a Quantum Design PPMS-9T system, respectively. From the XRD results, it was found that the phases of all of the samples consisted of the fluorite-type face-centered cubic δ-Bi{sub 2}O{sub 3} phase. It was observed that the microstructure of the samples is uniformly distributed on the samples’ surface. The temperature dependence of magnetization (M–T) measurements showed that the magnetization rose sharply at the critical temperature. The calculated critical temperature values vary from 22.19 to 56.61 K for the samples. All of the samples displayed the paramagnetic behavior. The paramagnetic behavior started from 300 K to very low temperature which varied from 22.19 to 56.61 K. The coercive rise on the magnetization below 22.19 K or 56.61 K with decreasing temperature causes a phase transformation in the δ-Bi{sub 2}O{sub 3} system. This sudden increment was considered as a ferromagnetic or ferrimagnetic phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Electronic and Magnetic Properties of Oligomers and Chains of Poly(benzodifurandione) (PBDF), A Highly Conducting n-Type Polymer

The seminal development of highly electrically conducting polyacetylene via oxidative or reductive treatment (“doping”) has continuously inspired the search for other conducting π-conjugated polymers. Recently, poly(benzodifurandione), PBDF, was reported to have unexpected solubility given the absence of side chains and to exhibit an unprecedented, high electrical conductivity upon reduction (“n-doping”), with protons acting as counterions. Here, we theoretically investigate the electronic and magnetic properties of PBDF by taking long oligomers and one-dimensional (1D) periodic chains as model systems. With the oligomer models, we characterize the formation of polarons and bipolarons in n-doped PBDF. Our results indicate that singlet bipolarons tend to be the energetically most favorable species when protons bind to two closely located carbonyl groups in nearest-neighbor benzodifurandione moieties. The calculations on the 1D periodic chain models show that the positions of the protonated carbonyl groups determine the metallic, semiconducting, or insulating nature of a PBDF chain. When the protonated carbonyl groups are all situated on the same side of a PBDF chain, a stable helical chain configuration is found that exhibits ferromagnetic behavior. Our findings elucidate the mechanism of polaron and bipolaron formation in long oligomers of n-doped PBDF and highlight the fascinating electronic and magnetic properties of periodic 1D chains. Furthermore, these studies also provide a stepping stone for investigations of PBDF thin films, for which two- and three-dimensional structures must be considered.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Enhancement in hard magnetic properties of (Nd, Pr)–Fe–B melt-spun ribbons

The coercivity of RE 2 Fe 14 B-type permanent magnets is strongly influenced by the microstructural features such as grain boundary (GB) phases as well as grain sizes. Here, we have combined micromagnetic simulations and experiments to elucidate the role of excess RE (Nd/Pr) in determining the resulting hard magnetic properties of Nd–Pr–Fe–B melt-spun ribbons. The intrinsic coercivity (H c ) at room temperature significantly enhanced from 9.7 kOe to 15.3 kOe with the increase in the Nd/Pr content. Furthermore, the effect of non-magnetic grain refining refractory carbide (TiC) on both the microstructure and magnetic hardening was studied. The addition of TiC showed a very high coercivity H c of up to 19.0 kOe at room temperature. Micromagnetic simulation indicates that the coercivity enhancement is mainly due to the reduction of inter-grain magnetic interaction, which is due to the RE-rich nonmagnetic grain boundary (GB) phase and/or TiC distributed at the GB. This work provides useful information on the roles of non-magnetic grain boundary phases for improving the coercivity of Nd–Pr–Fe–B magnets. Combined with experimental and modeling results, we have discussed the mechanism responsible for the enhancements in coercivity and the suitability of the alloys for high-performance permanent magnet development.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Magnetic Properties of Ba{sub 0.95}Y{sub 0.05}Fe{sub 12−x}Co{sub x}O{sub 19} Hexaferrites

Magnetoplumbite-type (M-type) barium ferrites doped with different Y–Co doping content Ba{sub 0.95}Y{sub 0.05}Fe{sub 12−x}Co{sub x}O{sub 19} (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) were successfully prepared by ceramic process and investigated in this paper for the first time. X-ray diffraction were used to analyze the phase of the prepared sample. The scanning electron microscopy (SEM) was used to measure the morphology, and magnetic properties were measured by vibrating sample magnetometer (VSM). The results of XRD show that the single phase of M-type barium ferrites was obtained with the increase of Co content (x), but α-Fe{sub 2}O{sub 3} occurred when x exceeds 0.3. The SEM results exhibit the uniform plane hexagonal structures of M-type ferrites with all range of Co doping content. VSM results display that magnetization (M{sub s}) and coercivity (H{sub c}) show the same tendency that their values first increase and then decrease with the increase of Co content.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Intrinsic Defects on Electronic and Magnetic Properties in Tm-Doped GaN: First-Principles Calculations

Based on the density functional theory, we investigate the electronic and magnetic properties of various types of defect complexes formed by dopant Tm and Ga vacancies, N vacancies, or O interstitial in Tm-doped GaN. Formation energies are first calculated for all defect complexes to assess their stability. The single Tm dopant is found to introduce the local magnetic moment of about 2 μ{sub B}/Tm in GaN. However, in the case of defect complexes, the magnetic moments of Tm can be suppressed by the existence of Ga vacancies around it, while the presence of N vacancies or O interstitial does not influence the magnetic moment of Tm. In addition, each Ga vacancy in the neutral charge state induces the local magnetic moment of about 2.1 μ{sub B} and one octahedral O interstitial can lead to the local moment of about 1.6 μ{sub B}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Theoretical Prediction of Structural, Electronic, and Magnetic Properties of Rh{sub 2}YIn (Y = Nd, Sm) Full-Heusler Alloys

We have studied the structural, electronic, and magnetic properties of Rh{sub 2}YIn (Y = Nd, Sm) alloys based on rare earth elements, using the full-potential linearized augmented plane-wave method (FP-LAPW) implemented in the Wien2K computer code with the parameterization of the generalized gradient approximation (GGA) and the local density approximation (LDA). Our results reveal a metallic behavior for rare earth-based full-Heusler Rh{sub 2}YIn (Y = Nd, Sm) alloys. Indeed, the structure of the state density illustrates a polarization for the up orientation (metal character) and a pseudo gap at the down orientation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of oxygen vacancies and Ag deposition on the magnetic properties of Ag/N co-doped TiO2 single-crystal films

Highlights: • Photochemical deposition method to prepare Ag-doped TiO{sub 2} samples. • TiO{sub 2} single crystal films are used for studying room temperature ferromagnetism origin. • Ag element is deposited on TiO{sub 2} single crystal films surface in the form of Ag particles. • Oxygen vacancies and Ag particles synergy influence the ferromagnetism in samples. - Abstract: We employ TiO{sub 2} single-crystal films as a substrate and use a photochemical deposition method to prepare Ag-doped and Ag/N co-doped TiO{sub 2} single-crystal films. We also investigate the optical and magnetic properties of the samples using various measurements. No diffraction peaks related to silver oxide appear in the X-ray diffraction (XRD) spectra, which implies the existence of Ag atoms in Ag-doped TiO{sub 2} single-crystal films. X-ray photoelectron spectroscopy (XPS) spectra indicate the existence of Ti{sup 4+} and Ag° in Ag/N co-doped TiO{sub 2} single-crystal films. It is found that Ag is deposited on a TiO{sub 2} single-crystal film surface in the form of Ag particles. Meanwhile, Ag particles can slightly enhance ferromagnetism in Ag-doped TiO{sub 2} single-crystal films compared with the TiO{sub 2} single-crystal film sample. Oxygen vacancies and Ag particle synergy influence ferromagnetism in Ag/N co-doped TiO{sub 2} single-crystal films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of Thickness on Structural and Magnetic Properties of Co-rich Bi{sub 10}Co{sub 16}O{sub 38} Sillenite Thin Films

The effect of thickness on structural and magnetic properties of Co-rich Bi{sub 10}Co{sub 16}O{sub 38} (BCO) sillenite thin films is investigated systematically. BCO thin films are deposited using a simultaneous evaporation of Bi{sub 2}O{sub 3}, Co targets with RF-DC magnetron sputtering along with post-annealing procedure. The magnetic studies reveal an ordered magnetic nature below film thicknesses of 100 nm. Further, the temperature-dependent and field-dependent magnetic data is evaluated to comprehend the microstructure impact on to the magnetic nature of Co-rich sillenite thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tailoring the Structural, Optical and Magnetic Properties of NiFe{sub 2}O{sub 4} by Varying Annealing Temperature

Magnetic nanocrystalline NiFe{sub 2}O{sub 4} nanoparticles of size ranging between 13 and 19 nm were synthesized by the hydrothermal method using polyethylene glycol (PEG) as surfactant. The role of annealing on phase, crystallite size, and morphology was determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Energy-dispersive X-ray spectroscopy (EDX) was used for qualitative analysis. X-ray diffraction confirmed the single phase of as-obtained particles. TEM revealed a spherical morphology having an average particle size of 13.73 nm at 523 K and rises to 14.89, 16.42, and 21.14 nm at 623, 723, and 823 K respectively, which is approximately the same as the crystallite size determined from XRD. EDX results confirmed that elemental ratios were in stoichiometry. Fourier transform infrared (FTIR) spectral analysis demonstrates the formation of M-O bond in NiFe{sub 2}O{sub 4} nanoparticles. The optical spectra obtained from UV-visible spectroscopy revealed that nanoparticles have direct allowed energy band gap of 2.34, 2.47, 2.70, and 2.20 eV at 523, 623, 723, and 823 K respectively. A vibrating sample magnetometer (VSM) was used at room temperature for magnetic measurements which further showed ferromagnetic behavior of as-synthesized material. In addition, it was found that saturation magnetization increases with an increase of annealing temperature while coercivity decreases with temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effects of Laser-Cutting and Spark Erosion Techniques and Heat Treatment on the Magnetic Properties of Grain-Oriented Transformer Steels

Spark erosion and laser-cutting processes were examined in terms of their effects on the magnetic properties of grain-oriented electrical steels at working frequencies. The maximum permeability value in each case was considered a reference to determine the quantitative effect of cutting and eroding methods as well as the effects of heat treatment. To minimize the deterioration that appears after the piercing process is implemented, the specimens were subjected to heat treatment at the most appropriate temperature. The influence of stress-relief annealing could be observed throughout the domain refinement on the surface by using magneto-optical Kerr microscopy. Additionally, it was clearly seen that the domain contrast at the cut edge of the spark-eroded sample was more uniform than that provided by laser cutting upon applying a high AC-field amplitude.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Pressure-Dependent Magnetic Properties of Quasi-2D Cr 2 Si 2 Te 6 and Mn 3 Si 2 Te 6

Recently, pressure has been used to induce structural and magnetic phase transitions in many layered quantum materials whose layers are linked by van der Waals forces. Materials with such weakly held layers allow for relatively easy manipulation of the superexchange mechanism, which can give rise to novel magnetic behavior. Here, using hydrostatic pressure as a disorderless means to manipulate the interlayer coupling, we applied pressure on two quasi-2D sister compounds, namely, Cr 2 Si 2 Te 6 (CST) and Mn 3 Si 2 Te 6 (MST), up to ~1 GPa. Magnetic property measurements with the application of pressure revealed that the ferromagnetic transition temperature decreases in CST, while the opposite occurs for the ferrimagnetic MST. In MST, magnetization decreases with the increase in pressure, and such a trend is not clearly observed within the pressure range studied for CST. The overall pressure effect on magnetic characteristics such as exchange couplings and magnetic anisotropy energies is also examined theoretically using density functional theory. Exchange coupling in MST is strongly frustrated, and the first nearest neighbor interaction is the most dominant of the components with the strongest pressure dependence. In CST, the exchange coupling parameters exhibit very little dependence on pressure. This combined experimental and theoretical work has the potential to expand to other relevant quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Influence of Mechanical Stresses on the Magnetic Properties of NiFe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} Films

We have studied the influence of mechanical stresses on the magnetic properties of nickel ferrite (NiFev) and cobalt ferrite (CoFe{sub 2}O{sub 4}) films deposited on sapphire substrates with a- and c-oriented step terrace nanostructures. It is established that compressive stresses favor enhancement of the coercive field in thin ferrite films in the strain direction. Films of magnetically soft nickel ferrite with a room-temperature coercive field of 32.5 mT were obtained.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Tuning the Structural and Magnetic Properties in Mixed Cation Mn x Co 2– x P 2 S 6

The metal thiophosphates (MTP), M 2 P 2 S 6, are a versatile class of van der Waals materials, which are notable for the possibility of tuning their magnetic properties with the incorporation of different transition-metal cations. Further, they also offer opportunities to probe the independent and synergistic role of the magnetically active cation sublattice when coupled to P 2 Q 6 polyhedra. Herein, we report the structural, magnetic, and electronic properties of the series of MTPs, Mn x Co 2– x P 2 S 6 ( x = 0.25, 0.5, 1, 1.5, 1.75) synthesized by the P 2 S 5 flux method. In this work, structural and elemental analysis indicates a homogeneous stoichiometry in the Mn x Co 2– x P 2 S 6 compounds. We observe that a correlation is apparent between the intensities of specific Raman modes and Raman shifts with respect to the alloying ratio between Mn and Co. Magnetic susceptibility measurements indicate that the alloyed systems adopt an ordered antiferromagnetic (AFM) configuration with a dependence of the Néel temperature on the alloying ratio. A possible magnetic frustration behavior was observed for the composition MnCoP 2 S 6 due to magnetic moment compensation as the alloying ratio between Mn and Co approaches parity. Interestingly, mixed oxidation states of the metal cation species are also observed in Mn x Co 2– x P 2 S 6 along with a linear dependence of the work function on the alloying ratio of Mn and Co.

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

Mean-Field and Monte Carlo Studies of the Magnetic Properties of a Spin-7/2 and Spin-5/2 Ising Bilayer Film

We use standard Monte Carlo simulations based on the Metropolis algorithm and mean-field calculations to investigate the magnetic properties of an Ising bilayer film consisting of two superposed ferromagnetic squared lattices A and B whose magnetic atoms have spin 7/2 and 5/2 respectively. Crystal-field and external magnetic field effects on the spins are considered in the model. The magnetic order parameters and response functions are calculated as functions of the temperature for selected values of the model parameters and this enables one to devise thermal phase diagrams by both methods. Our calculations only reveal second-order phase boundaries. Under appropriate conditions, compensation point phenomena are detected in the calculations below the critical temperatures. When the system is exposed to the external magnetic constraint, attracting hysteresis phenomena are sometimes generated. The temperature dependence of the coercitive field for various values of the crystal-field is singled out.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗