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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Acoustical “transparency” induced by local resonance in Bragg bandgaps

We show that sound waves can resonantly transmit through Bragg bandgaps in an acoustical duct periodically attached with an array of Helmholtz resonators, forming within the normally forbidden band a transparency window with group velocity smaller than the normal speed of sound. The transparency occurs for the locally resonant frequency so much close to the Bragg one that both the local-resonance-induced bandgap and the Bragg one heavily overlap with each other. The phenomenon seems an acoustical analog of the well-known electromagnetically induced transparency by quantum interference. Different from the Fano-like interference explanation, we also provide a mechanism for the transparency window phenomenon which makes it possible to extend the phenomenon in general.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A study of spin canting in Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} with Mössbauer spectroscopy under 5 T

Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} has been actively studied as a Lithium ion battery cathode material for the next-generation energy storage application. Here, we have investigated the changes of magnetic coupling between two different magnetic sub-lattices in Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} with x-ray diffraction (XRD), superconducting quantum interference device (SQUID), and Mössbauer spectroscopy measurements. The experimental XRD pattern was analyzed using Rietveld refinement, confirming single phase. In order to investigate the magnetic property, the SQUID measurement under applied field of 5 T was performed between 4.2 and 295 K. From the temperature-dependent zero-field-cooled and field-cooled magnetization curves, we observed the magnetization decreasing with increasing temperature up to T{sub min} = 13 K, at which the magnetization showed a minimum value. With continuing increase in temperature, the magnetization starts increasing with a maximum value at T{sub max} = 28 K and beyond T{sub max}, the magnetization decreases with the further increase in temperature. Based on the experimentally measured Mössbauer spectra, we identified that the ratios of first and sixth to second and fifth absorption lines were identical around T{sub min}, while with increasing temperature the area of second and fifth absorption line rapidly decreased up to T{sub max}. Our study suggests that the spin canting angle between the applied field and hyperfine field of Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} is constant up to T{sub min}. However, the spin canting angle starts decreasing with increasing temperature, reaching a minimum value at T{sub max}, and beyond T{sub max} it is increasing. We expect that around T{sub max}, the ferrimagnetically coupled spin arrangement is appeared to be collinear along the applied field direction under applied field of 5 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Large voltage modulation in magnetic field sensors from two-dimensional arrays of Y-Ba-Cu-O nano Josephson junctions

We have fabricated and tested two-dimensional arrays of YBa{sub 2}Cu{sub 3}O{sub 7−δ} superconducting quantum interference devices. The arrays contain over 36 000 nano Josephson junctions fabricated from ion irradiation of YBa{sub 2}Cu{sub 3}O{sub 7−δ} through narrow slits in a resist-mask that was patterned with electron beam lithography and reactive ion etching. Measurements of current-biased arrays in magnetic field exhibit large voltage modulations as high as 30 mV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Perpendicular magnetic anisotropy of Mn{sub 4}N films on MgO(001) and SrTiO{sub 3}(001) substrates

We grew Mn{sub 4}N epitaxial thin films capped with Au layers on MgO(001) and SrTiO{sub 3}(001) substrates by molecular beam epitaxy. Perpendicular magnetic anisotropy (PMA) was confirmed in all the samples at room temperature from the magnetization versus magnetic field curves using superconducting quantum interference device magnetometer. From the ω-2θ x-ray diffraction (XRD) and ϕ-2θ{sub χ} XRD patterns, the ratios of perpendicular lattice constant c to in-plane lattice constant a, c/a, were found to be about 0.99 for all the samples. These results imply that PMA is attributed to the in-plane tensile strain in the Mn{sub 4}N films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Fabrication and long-wavelength characterization of neat and chemically modified graphene

Graphene, a single- or several layer-thick carbon, attracts significant research activity because of its exceptional material properties. Graphene is a promising material for optoelectronic applications. Neat graphene demonstrates potential as a material for long wavelength photodetectors working at elevated temperatures. Chemical modification of graphene opens up many new applications of this material in electronics, in new composite materials, and in new catalysts for different chemical processes. Chemical vapor deposition-grown large-area graphene can be successfully modified with the creation of benzyne attachments. The investigation of microwave properties is an important part of graphene research. Two variants of near-field long wavelength microscopy were found efficient with graphene. Measurements with a probe formed by an electrically open end of a 4 GHz half-lambda parallel-strip transmission line resonator allow the implementation of an electrodynamic model of graphene microwave impedance. The results of near-field scanning superconducting quantum interference device (SQUID) RF microscopy of graphite and graphene at 200 MHz shed light on mechanisms of AC graphene response: screening currents induced in graphene by an external RF magnetic field tend to localize near structural defects.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Probing the thiol-gold planar interface by spin polarized tunneling

Reports of induced magnetism at thiol-gold interface have generated considerable recent interest. In these studies, the sample magnetization was generally measured by superconducting quantum interference device magnetometry which has limitation in determining surface and interface magnetism. In this work, we have fabricated planar tunnel junctions incorporating a thiol-gold interface. An observed room temperature humidity effect together with low temperature inelastic electron tunneling spectroscopy confirmed the existence of a thiol-gold interface in the organic-inorganic hybrid heterostructure. Spin polarized tunneling measurements were performed to probe the spin polarization at the thiol-gold interface; however, the obtained spin polarized tunneling spectra indicate no measurable spin polarization at the thiol-gold interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Fabrication and characterization of shunted μ-SQUID

In order to eliminate hysteresis, we have fabricated and characterized niobium based shunted micron size superconducting quantum interference devices (μ-SQUIDs). We find a wide temperature range where these μ-SQUIDs are non-hysteretic in nature and show a very good I{sub c} vs. B oscillations in hysteretic regime and V vs. B oscillations in non-hysteretic regime. Here we report the characteristics of a shunted- μ-SQUID (Wf38LS72D5). In this device we have achieved a large voltage modulation, in non-hysteretic regime, at various temperatures including such as 1.1 mV at 6.62 K with a transfer function V{sub Φ} = 7.2mV/Φ{sub 0}. The figures within the original article PDF file, as supplied to AIP Publishing, were affected by a PDF-processing error. Consequently, the article re-flowed and pagination increased from 3 to 4 pages. This article was updated on 14 May 2014 to correct the PDF-processing error, with the scientific content remaining unchanged. Readers are advised that the replacement article PDF file contains an additional blank page to preserve the original pagination.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Storage and on-demand release of microwaves using superconducting resonators with tunable coupling

We present a system which allows to tune the coupling between a superconducting resonator and a transmission line. This storage resonator is addressed through a second, coupling resonator, which is frequency-tunable and controlled by a magnetic flux applied to a superconducting quantum interference device. We experimentally demonstrate that the lifetime of the storage resonator can be tuned by more than three orders of magnitude. A field can be stored for 18 μs when the coupling resonator is tuned off resonance and it can be released in 14 ns when the coupling resonator is tuned on resonance. The device allows capture, storage, and on-demand release of microwaves at a tunable rate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Spin-resolved Fano resonances induced large spin Seebeck effects in graphene-carbon-chain junctions

We propose a high-efficiency thermospin device constructed by a carbon atomic chain sandwiched between two ferromagnetic (FM) zigzag graphene nanoribbon electrodes. In the low-temperature regime, the magnitude of the spin figure of merit is nearly equal to that of the corresponding charge figure of merit. This is attributed to the appearances of spin-resolved Fano resonances in the linear conductance spectrum resulting from the quantum interference effects between the localized states and the expanded states. The spin-dependent Seebeck effect is obviously enhanced near these Fano resonances with the same spin index; meanwhile, the Seebeck effect of the other spin component has a smaller value due to the smooth changing of the linear conductance with the spin index. Thus, a large spin Seebeck effect is achieved, and the magnitude of the spin figure of merit can reach 1.2 at T = 25 K. Our results indicate that the FM graphene-carbon-chain junctions can be used to design the high-efficiency thermospin devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structural, optical, and magnetic properties of highly-resistive Sm-implanted GaN thin films

Samarium ions of 200 keV in energy were implanted into highly-resistive molecular-beam-epitaxy grown GaN thin films with a focused-ion-beam implanter at room temperature. The implantation doses range from 1 × 10{sup 14} to 1 × 10{sup 16 }cm{sup −2}. Structural properties studied by x-ray diffraction and Raman-scattering spectroscopy revealed Sm incorporation into GaN matrix without secondary phase. The optical measurements showed that the band gap and optical constants changed very slightly by the implantation. Photoluminescence measurements showed emission spectra similar to p-type GaN for all samples. Magnetic investigations with a superconducting quantum interference device identified magnetic ordering for Sm dose of and above 1 × 10{sup 15 }cm{sup −2} before thermal annealing, while ferromagnetism was only observed after thermal annealing from the sample with highest Sm dose. The long-range magnetic ordering can be attributed to interaction of Sm ions through the implantation-induced Ga vacancy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Magnetic anisotropy in ultrathin Fe films on GaAs, ZnSe, and Ge (001) substrates

We discuss magnetic anisotropy parameters of ferromagnetic body-centered cubic (bcc) Fe films grown by molecular beam epitaxy (MBE) on (001) substrates of face-centered cubic (fcc) GaAs, ZnSe, and Ge. High-quality MBE growth of these metal/semiconductor combinations is made possible by the fortuitous atomic relationship between the bcc Fe and the underlying fcc semiconductor surfaces, resulting in excellent lattice match. Magnetization measurements by superconducting quantum interference device (SQUID) indicate that the Fe films grown on (001) GaAs surfaces are characterized by a very strong uniaxial in-plane anisotropy; those grown on (001) Ge surfaces have a fully cubic anisotropy; and Fe films grown on ZnSe represent an intermediate case between the preceding two combinations. Ferromagnetic resonance measurements carried out on these three systems provide a strikingly clear quantitative picture of the anisotropy parameters, in excellent agreement with the SQUID results. Based on these results, we propose that the observed anisotropy of cubic Fe films grown in this way results from the surface reconstruction of the specific semiconductor substrate on which the Fe film is deposited. These results suggest that, by controlling surface reconstruction of the substrate during the MBE growth, one may be able to engineer the magnetic anisotropy in Fe, and possibly also in other MBE-grown ferromagnetic films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Proximity nanovalve with large phase-tunable thermal conductance

We propose a phase-controlled heat-flux quantum valve based on the proximity effect driven by a superconducting quantum interference proximity transistor (SQUIPT). Its operation relies on the phase-dependent quasiparticle density of states in the Josephson weak-link of the SQUIPT which controls thermal transport across the device. In a realistic Al/Cu-based setup the structure can provide efficient control of thermal current inducing temperature swings exceeding ∼100 mK, and flux-to-temperature transfer coefficients up to ∼500 mK/Φ{sub 0} below 100 mK. The nanovalve performances improve by lowering the bath temperature, making the proposed structure a promising building-block for the implementation of coherent caloritronic devices operating below 1 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Interplay between snake and quantum edge states in a graphene Hall bar with a pn-junction

The magneto- and Hall resistance of a locally gated cross shaped graphene Hall bar is calculated. The edge of the top gate is placed diagonally across the center of the Hall cross. Four-probe resistance is calculated using the Landauer-Büttiker formalism, while the transmission coefficients are obtained using the non-equilibrium Green's function approach. The interplay between transport due to edge channels and snake states is investigated. When two edge channels are occupied, we predict oscillations in the Hall and the bend resistance as function of the magnetic field, which are a consequence of quantum interference between the occupied snake states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The atomic magnetometer: A new era in biomagnetism

The high cost and impracticality of SQUID (Superconducting QUantum Interference Device) magnetometers has limited the expansion of magnetoencephalography (MEG) and magnetocardiography (MCG), especially in countries where the cost of liquid helium is high. A recent breakthrough, however, has the potential to radically change this situation. In 2003, a group at Princeton University demonstrated an atomic magnetometer, known as the SERF (spin-exchange free relaxation) magnetometer, with unprecedented sensitivity. Since then, several research groups have utilized SERF magnetometers to record MEG, MCG, and fetal MCG signals. Despite some modest drawbacks, it now seems almost certain that SERF magnetometers can replace SQUIDs for many applications. With a price tag that is likely to be far less than that of SQUIDs, SERF magnetometers can propel the next wave of growth in biomagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

High-sensitivity cooled coil system for nuclear magnetic resonance in kHz range

In several low-field Nuclear Magnetic Resonance (LF-NMR) and surface nuclear magnetic resonance applications, i.e., in the frequency range of kHz, high sensitivity magnetic field detectors are needed. Usually, low-T{sub c} superconducting quantum interference devices (SQUIDs) with a high field sensitivity of about 1 fT/Hz{sup 1/2} are employed as detectors. Considering the flux trapping and operational difficulties associated with low-T{sub c} SQUIDs, we designed and fabricated liquid-nitrogen-cooled Cu coils for NMR detection in the kHz range. A cooled coil system consisting of a 9-cm diameter Cu coil and a low noise preamplifier was systematically investigated and reached a sensitivity of 2 fT/Hz{sup 1/2} at 77 K, which is 3 times better compared to the sensitivity at 300 K. A Q-switch circuit as an essential element for damping the ringing effects of the pickup coil was developed to acquire free induction decay signals of a water sample with minimum loss of signal. Our studies demonstrate that cooled Cu coils, if designed properly, can provide a comparable sensitivity to low-T{sub c} SQUIDs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Note: Optical receiver system for 152-channel magnetoencephalography

An optical receiver system composing 13 serial data restore/synchronizer modules and a single module combiner converted optical 32-bit serial data into 32-bit synchronous parallel data for a computer to acquire 152-channel magnetoencephalography (MEG) signals. A serial data restore/synchronizer module identified 32-bit channel-voltage bits from 48-bit streaming serial data, and then consecutively reproduced 13 times of 32-bit serial data, acting in a synchronous clock. After selecting a single among 13 reproduced data in each module, a module combiner converted it into 32-bit parallel data, which were carried to 32-port digital input board in a computer. When the receiver system together with optical transmitters were applied to 152-channel superconducting quantum interference device sensors, this MEG system maintained a field noise level of 3 fT/√Hz @ 100 Hz at a sample rate of 1 kSample/s per channel.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗