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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Preparation of Cr{sup 3+}-Substituted NiFe{sub 2}O{sub 4} Nanoparticles and Its Microwave Absorption Properties

In the present work, spinel Ni{sub (1−X)}Cr{sub X}Fe{sub 2}O{sub 4} (X = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 M) nanoparticles were synthesized by co-precipitation method followed by calcination at 400 °C for 2 h. The structural and morphological properties of the synthesized nanoparticles were studied using powder XRD,micro-Raman measurements, FE-SEM, TEM and EDS. The results revealed that the synthesized nanoparticles were single-crystal, cubic-phase structure with spherical shape. Energy-dispersive X-ray spectroscopy confirmed the elements present in the synthesized nanoparticles. Moreover, microwave absorption properties were measured using vector network analyser (VNA). The minimum reflection loss − 14.44 dB at 9.49 GHz was observed for Ni{sub (1−X)}Cr{sub X}Fe{sub 2}O{sub 4} (X = 0.5 M) nanoparticles at 3 mm thickness. These results suggest that Ni{sub (1−X)}Cr{sub X}Fe{sub 2}O{sub 4} (X = 0.5 M) nanoparticles would be applicable for microwave absorption application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Thermal Transport Measurements of LaCoO{sub 3} and SrTiO{sub 3}

Thermal conductivity and thermopower measurements as functions of temperature were carried out on SrTiO{sub 3} single crystals below room temperature and compared to those obtained for LaCoO{sub 3} polycrystalline samples. The maximum value of thermal conductivity for SrTiO{sub 3} (110) and Nb-doped SrTiO{sub 3} single crystals was 1.09 and 0.91 W/mK, respectively, at 300 K. The thermopower measurements were − 5.47 and − 41.17 μ V/K, respectively, at 300 K. This indicates the predominance of negative charge carriers or electrons in the material. Measurements on LaCoO{sub 3} polycrystalline samples yielded maximum values of 0.37 W/mK and 620 μ V/K for thermal conductivity and thermopower, respectively. These positive values suggest that positive charge carriers are predominant or that the compound is slightly hole-doped. We studied the effect of Nb doping on the thermopower and thermal conductivity of SrTiO{sub 3} and contrasted the results obtained with similar measurements on LaCoO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

{sup 125}Te-NMR Study in Novel Superconductor Pb{sub 1−x}Tl{sub x}Te with Valence Skipping Dopants

Pb{sub 1−x}Tl{sub x}Te is an anomalous low carrier density superconductor for which the origin of the superconductivity is not understood. Thallium is the only dopant to cause superconductivity in PbTe, suggesting that these specific impurities have a unique effect on the electronic states. Systematic {sup 125}Te-NMR studies on single-crystallines Pb{sub 1−x}Tl{sub x}Te (x = 0, 0.35, 1.0 at%) reveal that the Tl dopants induce spatially inhomogeneous electronic states around the Tl dopants. In the superconducting sample at x = 1.0 at%, {sup 125}Te nuclear spin relaxation rate (1/T{sub 1}T) in the vicinity of the Tl dopants is unexpectedly enhanced below ∼10 K. This coincides with the temperature below which the resistivity exhibits an upturn. By contrast, such anomalies were not detected in the non-superconducting sample at x = 0.35 at%. These observations can be consistently explained by charge Kondo effect, in which two nearly degenerate valence states of the Tl dopant form a resonating valence state upon cooling below 10 K. Based on these observations, we suggest that the coherent hopping of 6s-electron pair may provide the pairing interaction (i.e., a negative-U scenario), leading to the anomalously high T{sub c} found for Pb{sub 1−x}Tl{sub x}Te.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Space-Modulated Structures in BiFeO{sub 3} Films

In this work, we explore the properties of antiferromagnetic cycloid and the phase transitions between commensurate and incommensurate magnetic states in epitaxial BiFeO{sub 3} film. Additional magnetic anisotropy induced by strain effects in the films allocates cycloids with the definite directions of spin rotation. Peculiar feature of the cycloids propagating in the films whose symmetry is different from the single crystals is the orientation of spin rotational plane that does not contain electric polarization in contrast with the bulk materials. We construct a diagram of phase transitions induced by magnetic field applied along normal to the surface and show considerable decrease of the strength of magnetic field destroying cycloid in films compared with the bulk.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Interface-Induced and Interface-Enhanced Superconductivity

Among the various theoretical mechanisms proposed to reach a higher Tc, the interface mechanism in different forms has been the one most explored, and it provides continual inspiration and hope for realizing the ultimate goal for researchers in the superconductivity field—room-temperature superconductivity. Difficulties do exist, as most of the materials proposed to exhibit the interfacial mechanism are artificially formed heterostructures and are by nature delicate and easily disturbed by strain and change in the stoichiometry at the interface. The discoveries of superconductivity in naturally assembled single crystals of rare earth (R)-doped CaFe2As2 (Ca122) with a Tc up to 49 K and undoped CaFe2As2 with a Tc up to 25 K have opened an alternate route to tackle the problem. The experimental observation has provided the most direct evidence for interface-induced superconductivity in Ca122 to date and possibly in R-doped Ca122. Given the fact that neither chemical doping nor the application of physical pressure has ever induced a Tc higher than 40 K in bulk FeSe, the reports of Tc up to 45–109 K in FeSe/STO thin films demonstrate that FeSe/STO is an ideal system in which to explore interface-enhanced superconductivity. Here we review the above three specific examples of our effort toward superconductors of higher Tc to demonstrate that the interface mechanism may be a promising paradigm to achieve higher Tc.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Substrate Temperature on Structural, Morphological, Magnetic, and Electrical Properties of Fe{sub 2}CoSi Heusler Alloy Thin Films for Spin-Based Device Applications

Fe{sub 2}CoSi based Heusler alloy thin films are deposited on single crystal Si (111) substrate at different substrate temperatures varying from room temperature to 600 °C using ultrahigh vacuum DC magnetron sputtering. Structural analysis of the prepared thin films is carried out using GI-XRD measurement and it conform ordered L2{sub 1} crystal structure of the films deposited at 450 °C and above. The atomic force microscopic (AFM) images of Fe{sub 2}CoSi thin films exhibiting 3D-like growth on Si (111) substrate at varying temperatures. The magnetic property of the thin films is studied using vibrating sample magnetometer (VSM). At 450 °C of substrate temperature, the prepared thin film exhibits high saturation magnetization (M{sub s} = 948 emu/cc) and low coercivity (H{sub c} = 8 Oe). The self-energy magnetization of the film and its own field is very high, when the temperature of the substrate was maintained at 450 °C and switching field ratio for this film was obtained as ~ 0.9 due to its high crystallinity and atomic ordering. The electrical property of Fe{sub 2}CoSi thin film is investigated using four-probe technique and a positive magnetoresistive behavior was observed for thin film deposited at a substrate temperature of 450 °C which indicates the possible half-metallic nature at room temperature. The enhanced magnetic and electrical properties obtained for the thin film prepared at 450 °C substrate temperature is highly suitable for spin based device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Growth, Characterization and High-Field Magneto-Conductivity of Co{sub 0.1}Bi{sub 2}Se{sub 3} Topological Insulator

We report the crystal growth as well as transport properties of Co added Bi{sub 2}Se{sub 3} (Co{sub 0.1}Bi{sub 2}Se{sub 3}) single crystals. The values of the lattice parameters for pure and Co added sample were nearly the same. The Raman spectroscopy displayed slightly higher Raman shift of corresponding A{sub 1g}{sup 1}, Eg{sup 2}, and A{sub 1g}{sup 2} vibrational modes for Co{sub 0.1}Bi{sub 2}Se{sub 3}, and the resistivity curves with and without applied magnetic field show a metallic behavior. Both the crystals were subjected to magneto-resistance (MR) measurements under applied fields of 14 T. The value of MR is found to decrease from about 380% (5 K, 14 T) for Bi{sub 2}Se{sub 3} to 200% for Co{sub 0.1}Bi{sub 2}Se{sub 3}. To elaborate the transport properties of pure and Co added Bi{sub 2}Se{sub 3} crystals, the magneto-conductivity is fitted to the HLN (Hikami-Larkin-Nagaoka) equation, and it is found that the charge conduction is mainly dominated by surface-driven WAL (weak anti-localization) with negligible bulk WL (weak localization) contribution in both crystals alike. The MH curves of Co{sub 0.1}Bi{sub 2}Se{sub 3} crystal at different temperatures displayed a combination of both ferromagnetic and diamagnetic behavior. On the other hand, the electron paramagnetic resonance (EPR) revealed that pure Bi{sub 2}Se{sub 3} is diamagnetic, whereas Co orders ferromagnetically with resonating field around 3422 Oe at room temperature. The calculated value of Lande “g” factor is around 2.04 ± 0.05. Summarily, the short letter discusses the interesting magneto-conductivity and complex magnetism of Co in Co{sub 0.1}Bi{sub 2}Se{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Non-resonant Microwave Absorption and Boundary Current Response of Ba{sub 0.34}K{sub 0.64}Fe{sub 2}As{sub 2} Superconducting Single Crystals

Boundary current response of Ba{sub 0.34}K{sub 0.64}Fe{sub 2}As{sub 2} (BaK122) single crystals was probed by non-resonant microwave absorption (NRMA) as a function of 100-KHz modulation field at an intermediate temperature, namely, 25 K, which is 10 K below the actual T{sub c}. The measurements were done for both field parallel and perpendicular to the iron arsenide plane configuration. A weak anisotropic effect is noted. However, it is observed that the boundary current response depends on the modulation field value and it increases as we increase the modulation field value from 1 to 9 G. Further, this boundary current response strongly depends on the microwave power. We have shown that these modulation field and microwave power dependence of the boundary current response of NRMA signals in BaK122 iron arsenide crystal can be qualitatively understood through the Dulcic model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Experimental Investigation on the Low-Temperature Anomalies in Dysprosium Iron Garnet (DyIG)

The anomalous physical properties of dysprosium iron garnet Dy{sub 3}Fe{sub 5}O{sub 12} or DyIG single crystals have been revisited at low temperatures. This paper presents results of experimental investigation based on specific heat, magnetization, and Faraday rotation measurements. The distinguishing features are the occurrence of two types of anomalies in the temperature dependences of some judicious quantities. The first one coincides with the previous first-order spin reorientation transition at T{sub SR} = 15 K where the iron sublattice magnetization vector M{sub Fe} changes from the <111> axis at high temperature toward the low angular phases below T{sub SR}. The second one takes place around the “low-temperature Belov point” T{sub B} = 42 K, confirming what had already been predicted previously about the paraprocess effect in this ferrimagnet. The results are compared with previous findings and discussed taking into account the coexistence of some concomitant phenomena such the magnetodielectric and Schottky effects which cause anomalies, respectively near T{sub SR} and T{sub B}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Hexanuclear and Heptanuclear Nickel(II) Complexes of with a Non-Schiff-Base Tetradentate Ligand: an Example of Slow Motion Ferromagnetic Phase Transition at Very Low Temperature

Hexanuclear and heptanuclear nickel(II) complexes with N,N′-bis(2-hydroxy-3,5-dimethylbenzyl-1,2-ethanediamine (H{sub 2}hdde), [Ni{sub 6}(hdde){sub 3}(OH){sub 4}(NO{sub 3}){sub 2}(H{sub 2}O){sub 2}]·2dmf (dmf = N,N-dimethylformamide) and [Ni{sub 7}(hdde){sub 3}(OH){sub 6}(dmac){sub 3}](ClO{sub 4}){sub 2} (dmac = N,N-dimethylacetamide), were investigated. The latter complex was newly synthesized and the single-crystal X-ray structure analysis revealed a wheel-shaped heptanuclear cluster. These complexes showed a ferromagnetic interaction in the temperature dependence of magnetic susceptibilities. The micro-SQUID data of the former complex did not show SMM property, whereas the AC susceptibility measurements suggested SMM-like behavior and the zero-field-cooled and field-cooled studies showed a ferromagnetic transition near 240 mK for the latter complex.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Characterizing the Josephson Effect on Ba-122 Single-Crystal Junctions

This paper presents c-direction hybrid Josephson junctions with base electrodes of Co:BaFe{sub 2}As{sub 2} single crystals. To realize Josephson junctions, it applies standard photolithography technologies and a newly developed surface polishing method that was used. As conventional isotropic s-wave superconductor counter electrodes used double layers of Pb/In. The artificial barrier for the tunneling junctions consists of a thin sputtered Ti layer or a thermally evaporated Al layer; both layers were used as an insulator barrier. For characterizing the Josephson effects with TiO{sub x} barrier, we could realize I{sub c}R{sub N} products of about 13.7 μV and unconventional I{sub c}-T dependencies. The formation of Shapiro steps under the influence of microwave irradiation and magnetic field to the junctions will be discussed as well.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Signatures of Quantum Transport Steps in Bi{sub 2}Se{sub 3} Single Crystal

We report signatures of quantum magneto transport steps in a Bi{sub 2}Se{sub 3} single crystal. The Bi{sub 2}Se{sub 3} crystal is grown by self-flux method through solid-state reaction. Details of its structural analysis along with physical properties in terms of low temperature and high field transport, thermal (heat capacity), Raman, X-ray photo electron and angle resolved photo electron spectroscopy were reported earlier (J. Sup. Novel. Mag. 30, 2031 2017). In a present short letter, we show the details of its 2 K and up to 14 Tesla magneto transport, exhibiting quantum transport (QT) like steps above say 11 Tesla field. The possible QT steps cannot be modelled with the SdH (Shubnikov-de Haas) or other possible quantum oscillations. The observed QT like steps are possibly the result of the mixed out-of-plane R{sub xy}(H) and in-plane R{sub xx}(H) contributions from the misaligned [00l] planes of the studied crystal and this may happen with other studied topological insulator (TI) crystals as well. Our careful assessment of crystal XRD data shows the same.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Signature of Ferromagnetic Phase at Low Temperature in Low-Doped La{sub 0.88}Ca{sub 0.12}MnO{sub 3} Single Crystal

The confirmation of ferromagnetism at low temperature in a low-doped manganites system is always debatable. It is for the first time, electrical, magnetic, and thermal properties have been measured for manganites single crystal of La{sub 0.88}Ca{sub 0.12}MnO{sub 3} by using a floating-zone method. The electrical resistivity shows a perceptible change of resistance at a low temperature which can be viewed as a signature of the ferromagnetic phase. The ferromagnetic phase of the investigated La{sub 0.88}Ca{sub 0.12}MnO{sub 3} single crystal with Curie temperature of T{sub C} = 120 K which is in closed agreement with ac-susceptibility measurement. An analysis of the specific heat suggests the transition peak (T{sub P}) coincides with the T{sub C} and attains 1.2 J mol{sup −1} K at 116 K. The magnetoresistance (MR) and temperature coefficient of resistance (TCR) were found to be 69% and 10% respectively, which expands its subtle potential for applications in spintronics and thermistor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Synthesis of the Orthorhombic Dy{sub 1−x}Ho{sub x}MnO{sub 3} Single Crystals and Study of Their Magnetic Properties

In this report, we prepared for the first time the orthorhombic Dy{sub 1−x}Ho{sub x}MnO{sub 3} single crystals with x = 0, 0.1, 0.2, 0.3, and 0.4 using the flux technique. The post-growth processing and chemical and structural characterization of the synthesized samples were performed. Also, we examined the samples obtained by their magnetic properties and the magnetic anisotropy in wide ranges of temperatures and magnetic fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Oxygen Vacancy-Induced Room Temperature Ferromagnetism in Rutile TiO{sub 2}

As oxygen vacancies play an important role in ferromagnetism of rutile TiO{sub 2}, a method of γ-ray irradiates rutile TiO{sub 2} single crystals was subtly proposed to study the effect of oxygen vacancies on magnetic properties. Remarkably, room temperature ferromagnetism was observed in γ-ray irradiated rutile TiO{sub 2} single crystals, and the saturation magnetization is the strongest when dose is 4 × 10{sup 4} Gy which assigned to ESR results. Since the displacement threshold energy of Ti atom is much bigger than that of O atom, the defects produced by γ-irradiation are mainly oxygen vacancies. After irradiation, XPS, PL spectra indicate the presence of oxygen vacancies(V{sub O}), Ti{sup 3+}, and V{sub O}-Ti{sup 3+} composite defects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nonlinear Second Harmonics of Localized Shear Waves in an Anisotropic Layer Between Anisotropic Half Spaces Under the Conditions of Imperfect Contact

We construct a numerical-analytic solution of the problem of generation of the nonlinear second harmonics in the course of propagation of elastic symmetric localized shear waves in the crystalline layer of cubic system of the m3m class located between the crystalline half spaces of the same type and the same class of anisotropy under the conditions of imperfect sliding contact of components of the waveguide. We determine the analytic form of the functions of wave motions for nonlinear anharmonic perturbations in the form of longitudinal-shear-type waves. We also perform the numerical investigations of the amplitude-frequency characteristics of the second harmonics for monochromatic localized waves in a layer of a single crystal of germanium between the half spaces from the single crystal of silicon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Hybrid CdS nanowires/Si heterostructure photodetector fabricated by intense pulsed light assisted - laser ablation in liquid

Synthesis of CdS nanowires NWs by combined intense pulsed light (IPL) and pulsed laser ablation in liquid is demonstrated for the first time. An IPL source providing 3 ms duration pulses was used to assist the synthesis of CdS nanowires by 7 ns pulsed laser ablation of cadmium target in thiourea and CTAB solution. The results showed a small increase in optical energy band gap of CdS NWs and a decrease of the nanowires diameter from 50 to 40 nm after combining the IPL. The intensity of the photoluminescence emission peak located at 458 nm was doubled when the IPL combined laser ablation process. In addition the synthesized CdS nanowires showed single crystalline pure hexagonal wurtzite phase with decreased particles agglomeration and smaller particle size. Raman spectra were improved too by revealing sharp and shifted peaks at 293 and 585 cm{sup −1}. The figures of merit of hybrid n-CdSNWs/p-Si heterojunction photodetector namely responsivity and minority carrier lifetime were found to be improved remarkably after using IPL assisted laser ablation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Synthesis and structural features of new pentacoordinated monofluorosilanes containing C,O-chelate ligands based on 2-amino acid N-methylamides

Pentacoordinated monofluorosilanes R{sup 1}SO{sub 2}NHCHR{sub 2}C(O)N(Me)CH{sub 2}SiMe{sub 2}F containing moieties of N′-methyl-N-(organosulfonyl)-2-amino acid amides of glycine, alanine, and leucine as C,O-chelating ligands were synthesized via the reaction of corresponding disiloxanes with BF{sub 3}•Et{sub 2}O. The structures of obtained compounds were investigated by single-crystal X-ray diffraction analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗