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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Dielectric and magnetic properties of CoFe2O4 prepared by sol-gel auto-combustion method

Cobalt ferrite powders were successfully synthesized by sol-gel auto-combustion method. Influence of sintering temperature on structural, magnetic and dielectric properties was studied. All the obtained samples are spinel ferrite with a cubic symmetry. As the sintering temperature increased from 900 °C to 1300 °C, the average grain size increased from 0.26 μm to 0.83 μm. The dielectric constant and loss tangent measurement showed strong temperature dependence at all frequencies. The maximum magnetization increased while the coercivity and remanent magnetization decreased with the increasing sintering temperature. The non-saturation at high fields may be related to the surface effects in CoFe{sub 2}O{sub 4} samples. When sintered at 1300 °C, the sample showed a maximum magnetization value of ∼87.32 emu/g at room temperature. The highest value of coercivity of all the samples was 1368.33 Oe for the sample sintered at 900 °C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Li 4 Ru 2 OCl 10 ·10H 2 O: crystal structure, magnetic properties and bonding interactions in ruthenium-oxo complexes

The results of the structural determination, magnetic characterization, and theoretical calculations of a new ruthenium-oxo complex, Li 4 [Ru 2 OCl 10 ]·10H 2 O, are presented. Single crystals were grown using solvent methods and the crystal structure was characterized by single crystal X-ray diffraction. Li 4 [Ru 2 OCl 10 ]·10H 2 O crystallizes into a low-symmetry triclinic structure ($P\bar1$) due to the much smaller Li + cation compared to K + cation in the tetragonal complex K 4 [Ru 2 OCl 10 ]·H 2 O. The X-ray photoelectron spectra confirm only the single valent Ru 4+ in Li 4 [Ru 2 OCl 10 ]·10H 2 O even though two distinct Ru sites exist in the crystal structure. Magnetic measurements reveal the diamagnetic property of Li 4 [Ru 2 OCl 10 ]·10H 2 O with unpaired electrons existing on Ru 4+ . Furthermore, the molecular orbital analysis matches well with the observed UV and magnetic measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tuning the Magnetic Properties of CrI 3 Using Ni Thin Film Deposition for Applications in Spintronic Devices

Chromium triiodide (CrI 3 ), a van der Waals magnet, has recently been shown to host Ising ferromagnetism down to the monolayer limit. It is a potentially important material in 2D magnet-based applications, such as magnetic sensors and spintronic devices. Prior studies have revealed the coexistence of two different types of interlayer magnetic coupling, the antiferromagnetic (AFM) coupling near the surface and ferromagnetic (FM) coupling in the deep bulk layers, in pristine CrI 3 crystals below the Curie temperature. In this study, we used Ni thin film deposition to tune the surface magnetic states in bulk CrI 3 . A nanometer thickness (4 nm thick) of Ni was deposited on the surface of CrI 3 using electron-beam evaporation to form a Ni/CrI 3 heterostructure. The deposited Ni thin layer forms nanoclusters that completely cover the CrI 3 surface. Magnetic states of CrI 3 before and after Ni deposition are probed by ultralow-frequency magneto-Raman spectroscopy. Instead of seeing three spin wave branches in Raman scattering below 2 T, as in pristine bulk CrI 3 , in Ni/CrI 3 , we observe only a single spin wave branch, which is softened compared to that in pristine CrI 3 and displays a Zeeman shift under an out-of-plane magnetic field up to 7 T. This observation reveals that the AFM layers on pristine CrI 3 crystal surfaces transit into FM layers, so the entire CrI 3 crystal is in the FM state after Ni deposition. First-principles calculations show that Ni atoms tend to diffuse into the CrI 3 lattice, and the FM interlayer coupling has a much lower energy than AFM coupling in the presence of Ni atoms. As a result, our studies show that the magnetic state of CrI 3 can be modified through deposition of a thin metal layer on the surface, offering a route for controlling the spin degree of freedom in van der Waals magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic Properties of Some Tellurite Glasses

The AC magnetic susceptibility in the range 5–130 K of the tellurite glass systems: TeO{sub 2}–MnO{sub 2}–ZnO–PbO and TeO{sub 2}–MnO{sub 2}–V{sub 2}O{sub 5}–Fe{sub 2}O{sub 3} was measured and analyzed. The investigations of the AC magnetic susceptibility facilitated the determination of the molar susceptibility, paramagnetic magnetic susceptibility, paramagnetic Curie temperature, and magnetic entropy changes of the tellurite glasses. The results clarified that the temperature dependence of the magnetic susceptibility deviated from the Curie law and the increase of the small negative values of Curie temperature indicated negative interchange interactions between the antiferromagnetically coupled manganese ions within the present glass network. The magnetic moments evaluated from susceptibility measurements of the glasses show the predominance of the Mn{sup 2+} valence state than Mn{sup 3+} valence state of MnO{sub 2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Magnetic properties versus interface density in rigid-exchange-coupled amorphous multilayers with induced uniaxial anisotropy

We demonstrate the possibility to tune the saturation magnetization, coercivity, and uniaxial in-plane anisotropy constant in amorphous bilayers and multilayers of Co 85 (Al 70 Zr 30 ) 15 and Sm 11 Co 82 Ti 7 through the interface density. From magnetometry and x-ray circular dichroism (XMCD) measurements, we conclude that the easy-axis coercivity μ 0 H c increases four times when the number of bilayer repetitions, N, increases from 1 to 10 within a constant total sample thickness of 20 nm. At the same time, the anisotropy constant K u also increases by a factor four, whereas the saturation magnetization M s decreases slightly. The Co spin and orbital moments, m s and m l , are found to be approximately constant within the sample series. The average total Co moment is only 0.8-0.9 μ B /atom, but the m l /m s ratio is strongly enhanced compared to pure Co. Magnetization curves extracted from XMCD measurements show that the Co and Sm moments are ferromagnetically coupled for all samples.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Correlation of the Optical and Magnetic Properties of Bi{sub 2}Te{sub 3}–Sb{sub 2}Te{sub 3} Crystals

The magnetic and optical properties of Bi{sub 2}Te{sub 3}–Sb{sub 2}Te{sub 3} crystals are investigated depending on the ratio of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} components in the solid-solution composition and temperature. The results make it possible to affirm that an abrupt decrease in the magnetic-susceptibility anisotropy at T = 293 K is observed for samples, in which the electron–plasmon interaction is observed according to the data of optical studies. This is caused by the approaching energies of the plasmon and band-to-band transition which form the fundamental-absorption edge.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Elastic and Magnetic Properties of Cubic Fe{sub 4}C from First-Principles

First-principles calculations, based on density functional theory (DFT), are used to study the phase stability, elastic, magnetic, and electronic properties of cubic (c)-Fe{sub 4}C. Our results show that c-Fe{sub 4}C has ferromagnetic (FM) ground state as compared with antiferromagnetic (AFM) and nonmagnetic (NM) states. To study the phase stability of c-Fe{sub 4}C, BCC Fe{sub 4}C, FCC Fe{sub 4}C, and BCC Fe{sub 16}C, where C is considered at tetrahedral and octahedral interstitial sites, are also considered. The formation energy of c-Fe{sub 4}C is smaller than BCC Fe{sub 4}C but the shear moduli of c-Fe{sub 4}C is negative in both the FM and AFM states indicating that c-Fe{sub 4}C is dynamically not stable in the magnetic (FM/AFM) state. NM state has positive shear moduli which illustrates that the instability in c-Fe{sub 4}C is due to magnetism and can lead to soft phonon modes. The calculated formation energy also shows that c-Fe{sub 4}C has higher formation energy than the FCC Fe{sub 4}C indicating no possibility of c-Fe{sub 4}C in low carbon steels at low temperature. The magnetic moment of Fe in c-Fe{sub 4}C is also sensitive to lattice deformation and the electronic structure reveals the itinerant nature of electrons responsible for metallic behavior of c-Fe{sub 4}C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Preparation, Electrical and Magnetic Properties of Poly(m-phenylenediamine)/ZnFe{sub 2}O{sub 4} Nanocomposites

The different ratios of ZnFe{sub 2}O{sub 4} nanoparticles (10 and 20%) were wrapped on poly(m-phenylenediamine) through in situ oxidative polymerization method. The formation of PmPD/ZnFe{sub 2}O{sub 4} nanocomposites was confirmed through FTIR spectroscopy and XRD pattern. From the XRD results, the average crystalline size of ZnFe{sub 2}O{sub 4} nanoparticles and PmPD/ZnFe{sub 2}O{sub 4} nanocomposites were also calculated. The SEM image of ZnFe{sub 2}O{sub 4} nanoparticles shows granular morphology and FESEM images of PmPD/ZnFe{sub 2}O{sub 4} nanocomposites indicate the ZnFe{sub 2}O{sub 4} nanoparticles are agglomerated on PmPD matrix. The soft magnetic behavior of ZnFe{sub 2}O{sub 4} nanoparticles and PmPD/ZnFe{sub 2}O{sub 4} nanocomposites were observed from vibrating sample magnetometer. The dielectric properties of PmPD/ZnFe{sub 2}O{sub 4} nanocomposites were studied with different temperatures and frequencies. The magnetic properties of ZnFe{sub 2}O{sub 4} nanoparticles were also analyzed through Mössbauer spectroscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effects of Ho-ion substitution on the magnetic properties of the Ca3Co2O6 frustrated spin-chain compound

Highlights: • A great sensitivity of the Ca{sub 3}Co{sub 2}O{sub 6} magnetic behavior to the presence of magnetic foreign cation are emphasized. • As the Ho content increases the ferrimagnetic configuration becomes less stable; and the antiferromagnetic (AFM) interaction enhances gradually. • Antiferromagnetic coupling interaction between Ho{sup 3+} ions are interpreted, The complex micro-mechanism are discussed in detail. - Abstract: Ho{sup 3+}-ion doped spin-chain compounds Ca{sub 3}Co{sub 2-x}Ho{sub x}O{sub 6} (x = 0, 0.05, 0.1, 0.15) were prepared by a conventional solid-state reaction method. Rietveld refinement of the X-ray diffraction patterns at room temperature confirmed the rhombohedral structure with the R 3-bar c space group. The results reveal that the solid solubility of the Ho element in Ca{sub 3}Co{sub 2}O{sub 6} is in the range of x = 0.1–0.15. Magnetic measurement suggests that with the increased Ho content: (1) the ferromagnetic transition temperature Tc and spin freezing temperature T{sub ƒ} decrease obviously; (2) the ferrimagnetic configuration becomes less stable; (3) the dynamic characteristics become slower; and (4) the antiferromagnetic (AFM) interaction enhances gradually. Based on these phenomena, the mechanism was discussed in detail. The magnetic correlation length is broken at a low Ho{sup 3+}-ion level, and the Ho{sup 3+}-ion pair formation along the chain with a high level of doping was interpreted.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Manipulating the metal-to-insulator transition and magnetic properties in manganite thin films via epitaxial strain

Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of La 0.9 Ba 0.1 MnO 3 thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn eg orbitals can be switched from the d 3z 2 -r 2 orbital to the d x 2 -y 2 orbital by varying the strain from compressive to tensile. Further, the change of orbital occupancy associated with Mn 3d-O 2p hybridization leads to dramatic modulation of the magnetic and electronic properties of strained La 0.9 Ba 0.1 MnO 3 thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the La 0.9 Ba 0.1 MnO 3 system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Electric and Magnetic Properties of Bi{sub 2}Sr{sub 2}Ag{sub 0.03}Ca{sub 1}Cu{sub 2}O{sub y} Ceramics Modified by Post-annealing

Polycrystalline Bi{sub 2}Sr{sub 2}Ag{sub 0.03}Ca{sub 1}Cu{sub 2}O{sub y} samples were fabricated using conventional solid-state reaction method. Then, post-annealing temperatures at 730, 780 and 830 {sup ∘}C were applied on samples while time was kept constant at 50 h. Both the x-ray diffraction (XRD) measurement and the scanning electron microscopy (SEM) showed that all samples have high amounts of Bi-2212 phase as the main phase, indicating that the selected starting composition is suitable to analyze the post-annealing effects on the flux pinning properties of Bi-2212 superconductors. In particular, flux pinning performance of Bi-2212 phase is observed from both the magnetic hysteresis loops and J{sub c} values calculated using Bean’s model. The highest J{sub c} value was obtained for sample which was not exposed to the post-annealing treatment. The results clearly show that post-annealing procedure in Bi{sub 2}Sr{sub 2}Ag{sub 0.03}Ca{sub 1}Cu{sub 2}O{sub y} system does not create artificial pinning centres, which lead to the improvements in J{sub c} at high magnetic fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic Structures and Magnetic Properties of Transition Metal Doped CsPbI{sub 3} Perovskite Compounds by First-Principles Calculation

Transition metal doped cesium lead halide (CsPbI{sub 3}) perovskite compounds were studied for application in photovoltaic solar cells. Electronic structures, chemical shifts of {sup 207}Pb and {sup 127}I-NMR, vibration modes in infrared and Raman spectra of transition metals (Mn{sup 2+}, Fe{sup 2+} or Cu{sup 2+})-doped CsPbI{sub 3} perovskite compounds were studied by the first-principles calculation using density functional theory. The CsPb(Fe)I{sub 3} perovskite crystals had a slight perturbation of crystal field in the coordination structure. The electron density distribution was delocalized on the 5p orbital of I atom, the 3d orbital of Fe atom and the 6p orbital of Pb atom. The first excited process was based on ligand metal charge transfer from the 5p orbital on I atom to the 3d orbital of Fe atom. The chemical shifts of {sup 127}I-NMR were associated with the electron correlation of electron-nuclear spin interaction and nuclear quadrupole interactions based on electron field graduate. The asymmetric vibrations of Pb–I bonds stretching mode related to electron conductivity with scattering of the carrier diffusion as phonon effectiveness. The slight perturbation of the coordination structure in the CsPb(Fe)I{sub 3} perovskite crystal will improve the photovoltaic and optical properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Properties of La-Doped ZnO(0001)–Zn Polar Surface with and without Vacancies: a First-Principle Study

The effects of La doping with and without vacancies on the magnetism of a ZnO(0001)–Zn polar surface were studied using the generalized gradient approximation + U (GGA + U) method of density functional theory to determine the magnetism source of La-doped ZnO. Results revealed that La doping with O vacancy did not cause ZnO ferromagnetism, but La-doped ZnO with Zn vacancy was ferromagnetic. The net magnetic moment was primarily related to the unpaired electron amount of the O 2p state and slightly modified by orbital and anomalous magnetic moments. The anomalous magnetic moment originated from the radiating magnetism moment via quantum electrodynamics and was confirmed to exist via theoretical calculations of magnetism. Formation energy showed that La doping easily generated Zn vacancies in ZnO, but magnetic quenching occurred when the ratio of La ions to Zn vacancies was 2:1. The unpaired O 2p electrons induced by Zn vacancies were the magnetism source of La-doped ZnO. Moreover, the Curie temperature of La-doped ZnO with Zn vacancy reached room temperature. Results showed that the ZnO(0001)–Zn polar surface can be utilized as the surface of ZnO-based diluted magnetic semiconductors because of its unipolarity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Inkjet Printing of Magnetic Particles Toward Anisotropic Magnetic Properties

Unique properties of one-dimensional assemblies of particles have attracted great attention during the past decades, particularly with respect to the potential for anisotropic magnetism. Patterned films can be created using inkjet printing; however, drying of particle-laden colloidal droplets on solid surfaces is usually accompanied by the well-known coffee-ring effect, deteriorating both the uniformity and resolution of the printed configurations. Here, we examine the effect of externally applied magnetic field on particle deposition patterns. Ferromagnetic Gd 5 Si 4 particles were formulated in terpineol oil and directly deposited via magnetic field-assisted inkjet printing on a photopaper to generate patterned films with suppressed coffee-ring effect. The particle deposition morphology is determined by both solvent imbibition and particle-magnetic field interactions. Three characteristic times are considered, namely, the critical time for solvent imbibition into the substrate (t im ), the time it takes for particles to form chains in the presence of the magnetic field (t ch ), and the time in which the particles reach the substrate in the direction normal to the substrate (t pz ). The characteristic time ratios (t pz /t im ) and (t pz /t ch ) determine the final deposition morphology in the presence of magnetic field. Finally, the ability to control particle deposition and assembly, thus tuning the magnetic anisotropic properties of nanostructured materials is a promising approach for many engineering applications.

42 ENGINEERING↗
DOE OSTI2018

Magnetic properties of single crystalline itinerant ferromagnet AlFe 2 B 2

Here, single crystals of AlFe 2 B 2 have been grown using the self-flux growth method, and then we measured the structural properties, temperature- and field-dependent magnetization, and temperature-dependent electrical resistivity at ambient as well as high pressure. The Curie temperature of AlFe 2 B 2 is determined to be 274 K. The measured saturation magnetization and the effective moment for the paramagnetic Fe ion indicate the itinerant nature of the magnetism with a Rhode-Wohlfarth ratio M C /M sat ≈ 1.14. Temperature-dependent resistivity measurements under hydrostatic pressure show that transition temperature T C is suppressed down to 255 K for p = 2.24 GPa pressure with a suppression rate of ~–8.9 K/GPa. The anisotropy fields and magnetocrystalline anisotropy constants are in reasonable agreement with density functional theory calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of cobalt substitution on structure and magnetic properties of Nd 0.4 Zr 0.6 Fe 10–x Co x Si 2 (x = 0–3) alloys and their ribbons

This paper reports the stabilization of the RFe 12 -type based compounds where part of R and Fe are substituted with Zr and Co and Si, respectively, in order to examine whether these rare-earth-lean materials are suitable for applications as permanent magnets. Structural and magnetic characterization of the family of alloys with the general formula Nd 0.4 Zr 0.6 Fe 10–x Co x Si 2 (x = 0–3) and their melt-spun ribbons were carried out using X-ray diffraction and Mössbauer spectroscopy. The ThMn 12 -type structure is obtained for all samples as the majority phase with a minority α-Fe(CoSi) phase (less than 5 wt%) as it was estimated by XRD for x = 1 and 2. The Curie temperature increases linearly with Co substitution from 561 K for x = 0 to 712 K for x = 3. The saturation magnetization decreases slightly from 130.5 (x = 1) to 129.1 A·m 2 /kg (x = 3), while the anisotropy field is following the same trend.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗