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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Large amplitude oscillation of magnetization in spin-torque oscillator stabilized by field-like torque

Oscillation frequency of spin torque oscillator with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer is theoretically investigated by taking into account the field-like torque. It is shown that the field-like torque plays an important role in finding the balance between the energy supplied by the spin torque and the dissipation due to the damping, which results in a steady precession. The validity of the developed theory is confirmed by performing numerical simulations based on the Landau-Lifshitz-Gilbert equation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Calculation of energy-barrier lowering by incoherent switching in spin-transfer torque magnetoresistive random-access memory

To make a useful spin-transfer torque magnetoresistive random-access memory (STT-MRAM) device, it is necessary to be able to calculate switching rates, which determine the error rates of the device. In a single-macrospin model, one can use a Fokker-Planck equation to obtain a low-current thermally activated rate ∝exp(−E{sub eff}/k{sub B}T). Here, the effective energy barrier E{sub eff} scales with the single-macrospin energy barrier KV, where K is the effective anisotropy energy density and V the volume. A long-standing paradox in this field is that the actual energy barrier appears to be much smaller than this. It has been suggested that incoherent motions may lower the barrier, but this has proved difficult to quantify. In the present paper, we show that the coherent precession has a magnetostatic instability, which allows quantitative estimation of the energy barrier and may resolve the paradox.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Vulnerability of Karangkates dams area by means of zero crossing analysis of data magnetic

Study with entitled Vulnerability Karangkates Dam Area By Means of Zero Crossing Analysis of Data Magnetic has been done. The study was aimed to obtain information on the vulnerability of two parts area of Karangkates dams, i.e. Lahor dam which was inaugurated in 1977 and Sutami dam inaugurated in 1981. Three important things reasons for this study are: 1). The dam age was 36 years old for Lahor dam and 32 years old for Sutami dam, 2). Geologically, the location of the dams are closed together to the Pohgajih local shear fault, Selorejo local fault, and Selorejo limestone-andesite rocks contact plane, and 3). Karangkates dams is one of the important Hydro Power Plant PLTA with the generating power of about 400 million KWH per year from a total of about 29.373MW installed in Indonesia. Geographically, the magnetic data acquisition was conducted at coordinates (112.4149oE;-8.2028oS) to (112.4839oE;-8.0989oS) by using Proton Precession Magnetometer G-856. Magnetic Data acquisition was conducted in the radial direction from the dams with diameter of about 10 km and the distance between the measurements about 500m. The magnetic data acquisition obtained the distribution of total magnetic field value in the range of 45800 nT to 44450 nT. Residual anomalies obtained by doing some corrections, including diurnal correction, International Geomagnetic Reference Field (IGRF) correction, and reductions so carried out the distribution of the total magnetic field value in the range of -650 nT to 700 nT. Based on the residual anomalies, indicate the presence of 2 zones of closed closures dipole pairs at located in the west of the Sutami dam and the northwest of the Lahor dam from 5 total zones. Overlapping on the local geological map indicated the lineament of zero crossing patterns in the contour of residual anomaly contour with the Pohgajih shear fault where located at about 4 km to the west of the Sutami dam approximately and andesite-limestone rocks contact where located at about 6 km to the west of the Lahor dam approximately. These shown a possible of vulnerability on geohazards at the west zone of the Karangkates (Lahor-Sutami) dams area if there are triggers by the vibration (earthquake) on the Pohgajih shear fault, andesite-limestone contact plane, and instability rocks on two zones of closed closure dipole pairs area. Reality, on the location of the study shown some local landslide at the several locations and the main road that need considering for disaster mitigation.

58 GEOSCIENCES↗
DOE OSTI2015

Effect of Dzyaloshinskii-Moriya interaction on the magnetic vortex oscillator driven by spin-polarized current

By micromagnetic simulation, we investigated the dynamic of magnetic vortex driven by spin-polarized current in Permalloy nanodisks in the presence of interfacial/superficial Dzyaloshinskii-Moriya interactions (DMI). It is found that spin-polarized current can drive the vortex precession. In the presence of DMI, the oscillation frequency of the vortex is about 3 times higher than that of without DMI for the same nanodisk. Moreover, the linewidth is more narrow than that of without DMI when the radius of nanodisk is 50 nm. In addition, the vortex can support a higher current density than that of without DMI. Introduction of DMI in this system can provide a new way to design magnetic vortex oscillator.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Nonlinear dynamics of three-magnon process driven by ferromagnetic resonance in yttrium iron garnet

We report an investigation of the dynamics of the three-magnon splitting process associated with the ferromagnetic resonance (FMR) in films of the insulating ferrimagnet yttrium iron garnet (YIG). The experiments are performed with a 6 μm thick YIG film close to a microstrip line fed by a microwave generator operating in the 2–6 GHz range. The magnetization precession is driven by the microwave rf magnetic field perpendicular to the static magnetic field, and its dynamics is observed by monitoring the amplitude of the FMR absorption peak. The time evolution of the amplitude reveals that if the frequency is lowered below a critical value of 3.3 GHz, the FMR mode pumps two magnons with opposite wave vectors that react back on the FMR, resulting in a nonlinear dynamics of the magnetization. The results are explained by a model with coupled nonlinear equations describing the time evolution of the magnon modes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO{sub 2}/NiFe trilayers near simultaneous ferromagnetic resonance

The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-local SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO{sub 2} spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Neutron intensity modulation and time-focusing with integrated Larmor and resonant frequency techniques

The analysis of neutron diffraction experiments often assumes that neutrons are elastically scattered from the sample. However, there is growing evidence that a significant fraction of the detected neutrons is in fact inelastically scattered, especially from soft materials and aqueous samples. Ignoring these inelastic contributions gives rise to inaccurate experimental results. To date, there has been no simple method with broad applicability for inelastic signal separation in neutron diffraction experiments. Here, we present a simple and robust method that we believe could be suited for this purpose. We use two radio frequency resonant spin flippers integrated with a Larmor precession field to modulate the neutron intensity and to encode the inelastic scattering information into the neutron data. All three components contribute to the spin encoding. The Larmor field serves several additional purposes. Its usage facilitates neutron time-focusing, eliminates the need for stringent magnetic shielding, and allows for compact setups. The scheme is robust, simple, and flexible. We believe that, with further improvements, it has the potential of adding inelastic signal discrimination capabilities to many existing diffraction instruments in the future.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

All-optical evaluation of spin-orbit interaction based on diffusive spin motion in a two-dimensional electron gas

A method is presented that enables the measurement of spin-orbit coefficients in a diffusive two-dimensional electron gas without the need for processing the sample structure, applying electrical currents or resolving the spatial pattern of the spin mode. It is based on the dependence of the average electron velocity on the spatial distance between local excitation and detection of spin polarization, resulting in a variation of spin precession frequency that in an external magnetic field is linear in the spatial separation. By scanning the relative positions of the exciting and probing spots in a time-resolved Kerr rotation microscope, frequency gradients along the [100] and [010] crystal axes of GaAs/AlGaAs QWs are measured to obtain the Rashba and Dresselhaus spin-orbit coefficients, α and β. This simple method can be applied in a variety of materials with electron diffusion for evaluating spin-orbit coefficients.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Abnormal bias dependence of magnetoresistance in CoFeB/MgO/Si spin-injection tunnel contacts

We report a strong bias voltage dependence of magnetoresistance (MR) in CoFeB/MgO/Si spin-injection tunnel contacts using the three-terminal Hanle geometry. When a bias voltage is relatively large, the MR is composed of two characteristic signals: a conventional Hanle signal observed at a low magnetic field, which is due to the precession of injected spins, and another signal originating from the rotation of the magnetization at a larger magnetic field. In contrast, for a small bias voltage, additional signals appear at a wide range of magnetic fields, which occasionally overwhelms the conventional Hanle signals. Because the additional signals are pronounced at a low bias and are significantly reduced by annealing at moderate temperatures, they can be attributed to multi-step tunneling via defect states at the interfaces or tunnel barrier. Our results demonstrate that the spin injection signal caused by the defect states can be evaluated by its bias voltage dependence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Spin dynamics induced by ultrafast heating with ferromagnetic/antiferromagnetic interfacial exchange in perpendicularly magnetized hard/soft bilayers

The laser-induced spin dynamics of FeCo in perpendicularly magnetized L1{sub 0}-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting method for magnetization dynamics modulation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Stability of standing spin wave in permalloy thin film studied by anisotropic magnetoresistance effect

We have investigated the stability for the resonant spin precession under the strong microwave magnetic field by a specially developed detection method using the anisotropic magnetoresistance effect. The electrically separated excitation and detection circuits enable us to investigate the influence of the heating effect and the nonuniform spin dynamics independently. The large detecting current is found to induce the field shift of the resonant spectra because of the Joule heating. From the microwave power dependence, we found that the linear response regime for the standing spin wave is larger than that for the ferromagnetic resonance. This robust characteristic of the standing spin wave is an important advantage for the high power operation of the spin-wave device.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Combined effects of trapped energetic ions and resistive layer damping on the stability of the resistive wall mode

A dispersion relation is derived for the stability of the resistive wall mode (RWM), which includes both the resistive layer damping physics and the toroidal precession drift resonance damping from energetic ions in tokamak plasmas. The dispersion relation is numerically solved for a model plasma, for the purpose of systematic investigation of the RWM stability in multi-dimensional plasma parameter space including the plasma resistivity, the radial location of the resistive wall, as well as the toroidal flow velocity. It is found that the toroidal favorable average curvature in the resistive layer contributes a significant stabilization of the RWM. This stabilization is further enhanced by adding the drift kinetic contribution from energetic ions. Furthermore, two traditionally assumed inner layer models are considered and compared in the dispersion relation, resulting in different predictions for the stability of the RWM.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

About the parametrizations utilized to perform magnetic moments measurements using the transient field technique

The experimental study of nuclear magnetic moments, using the Transient Field technique, makes use of spin-orbit hyperfine interactions to generate strong magnetic fields, above the kilo-Tesla regime, capable to create a precession of the nuclear spin. A theoretical description of such magnetic fields is still under theoretical research, and the use of parametrizations is still a common way to address the lack of theoretical information. In this contribution, a review of the main parametrizations utilized in the measurements of Nuclear Magnetic Moments will be presented, the challenges to create a theoretical description from first principles will be discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Trapped fast particle destabilization of internal kink mode for the locally flattened q-profile with an inflection point

The destabilization of ideal internal kink modes by trapped fast particles in tokamak plasmas with a “shoulder”-like equilibrium current is investigated. It is found that energetic particle branch of the mode is unstable with the driving of fast-particle precession drifts and corresponds to a precessional fishbone. The mode with a low stability threshold is also more easily excited than the conventional precessional fishbone. This is different from earlier studies for the same equilibrium in which the magnetohydrodynamic (MHD) branch of the mode is stable. Furthermore, the stability and characteristic frequency of the mode are analyzed by solving the dispersion relation and comparing with the conventional fishbone. The results suggest that an equilibrium with a locally flattened q-profile, may be modified by localized current drive (or bootstrap current, etc.), is prone to the onset of the precessional fishbone branch of the mode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

THE COUNTERJET OF HH 30: NEW LIGHT ON ITS BINARY DRIVING SOURCE

We present new [S II] images of the Herbig-Haro (HH) 30 jet and counterjet observed in 2006, 2007, and 2010 that, combined with previous data, allowed us to measure with improved accuracy the positions and proper motions of the jet and counterjet knots. Our results show that the motion of the knots is essentially ballistic, with the exception of the farthest knots, which trace the large-scale 'C'-shape bending of the jet. The observed bending of the jet can be produced by a relative motion of the HH 30 star with respect to its surrounding environment, caused either by a possible proper motion of the HH 30 star, or by the entrainment of environment gas by the red lobe of the nearby L1551-IRS5 outflow. Alternatively, the bending can be produced by the stellar wind from a nearby classical T Tauri star, identified in the Two Micron All Sky Survey catalog as J04314418+181047. The proper motion velocities of the knots of the counterjet show more variations than those of the jet. In particular, we identify two knots of the counterjet that have the same kinematic age but whose velocities differ by almost a factor of two. Thus, it appears from our observations that counterjet knots launched simultaneously can be ejected with very different velocities. We confirm that the observed wiggling of the jet and counterjet arises from the orbital motion of the jet source in a binary system. Precession, if present at all, is of secondary importance in shaping the jet. We derive an orbital period of {tau}{sub o} = 114 {+-} 2 yr and a mass function of m{mu}{sup 3}{sub c} = 0.014 {+-} 0.006 M{sub Sun }. For a mass of the system of m = 0.45 {+-} 0.04 M{sub Sun} (the value inferred from observations of the CO kinematics of the disk), we obtain a mass of m{sub j} = 0.31 {+-} 0.04 M{sub Sun} for the jet source, a mass of m{sub c} = 0.14 {+-} 0.03 M{sub Sun} for the companion, and a binary separation of a = 18.0 {+-} 0.6 AU. This binary separation coincides with the value required to account for the size of the inner hole observed in the disk, which has been attributed to tidal truncation in a binary system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

ORBITS, MASSES, AND EVOLUTION OF MAIN BELT TRIPLE (87) SYLVIA

Sylvia is a triple asteroid system located in the main belt. We report new adaptive optics observations of this system that extend the baseline of existing astrometric observations to a decade. We present the first fully dynamical three-body model for this system by fitting to all available astrometric measurements. This model simultaneously fits for individual masses, orbits, and primary oblateness. We find that Sylvia is composed of a dominant central mass surrounded by two satellites orbiting at 706.5 {+-} 2.5 km and 1357 {+-} 4.0 km, i.e., about 5 and nearly 10 primary radii. We derive individual masses of 1.484{sup +0.016}{sub -0.014} Multiplication-Sign 10{sup 19} kg for the primary (corresponding to a density of 1.29 {+-} 0.39 g cm{sup -3}), 7.33{sup +4.7}{sub -2.3} Multiplication-Sign 10{sup 14} kg for the inner satellite, and 9.32{sup +20.7}{sub -8.3} Multiplication-Sign 10{sup 14} kg for the outer satellite. The oblateness of the primary induces substantial precession and the J{sub 2} value can be constrained to the range of 0.0985-0.1. The orbits of the satellites are relatively circular with eccentricities less than 0.04. The spin axis of the primary body and the orbital poles of both satellites are all aligned within about 2 deg of each other, indicating a nearly coplanar configuration and suggestive of satellite formation in or near the equatorial plane of the primary. We also investigate the past orbital evolution of the system by simulating the effects of a recent passage through 3:1 mean-motion eccentricity-type resonances. In some scenarios this allow us to place constraints on interior structure and past eccentricities.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

EXTENDED NEUTRAL HYDROGEN IN THE ALIGNED SHELL GALAXIES Arp 230 AND MCG -5-7-1: FORMATION OF DISKS IN MERGING GALAXIES?

As part of an ongoing study of the neutral hydrogen (H I) morphology and kinematics of 'shell' elliptical galaxies, we present Very Large Array observations of two shell galaxies with aligned shells, Arp 230 and MCG -5-7-1. Our data provide the first H I images of Arp 230 and deeper images of MCG -5-7-1 than previously reported. Optical images of Arp 230 reveal a bright, aligned, interleaved shell system, making it an ideal candidate for 'phase-wrapped' shell formation following a radial encounter with a smaller companion. The fainter, non-interleaved shells of MCG -5-7-1 do not clearly favor a particular formation scenario. The H I we detect in both galaxies extends to nearly the same projected distance as the optical shells. In Arp 230 this gas appears to be anti-correlated with the aligned shells, consistent with our expectations for phase-wrapped shells produced in a radial encounter. In MCG -5-7-1, we observe gas associated with the shells making a 'spatial wrapping' or looping scenario more plausible. Although the extended gas component in both galaxies is unevenly distributed, the gas kinematics are surprisingly regular, looking almost like complete disks in rotation. We use the H I kinematics and optical data to determine mass-to-light ratios M/L{sub B} of 2.4{sup +3.0}{sub -0.5} (at 13.5 kpc, 4.5 R{sub e} ) for Arp 230 and M/L{sub B} of 30 {+-} 7 (at 40 kpc, 7 R{sub e} ) in MCG -5-7-1. In both systems we find that this ratio changes as a function of radius, indicating the presence of a dark halo. By comparing orbital and precession timescales, we conclude that the potentials are slightly flattened. We infer a 5%-10% flattening for Arp 230 and less flattening in the case of MCG -5-7-1. Finally, we present images of the H I associated with the inner disk or (polar) ring of each galaxy and discuss possible explanations for their different present-day star formation rates. We detect total H I masses of 1.1 Multiplication-Sign 10{sup 9} M{sub Sun} in Arp 230 and 3.7 Multiplication-Sign 10{sup 9} M{sub Sun} in MCG -5-7-1. Both systems have H I masses, scale sizes, and regular kinematics similar to those of non-aligned shell galaxies we have previously studied (Cen A and NGC 2865). Furthermore, we (re-)emphasize in this paper that shell galaxies such as MCG -5-7-1, along with previously studied galaxies NGC 5128 (Cen A) and NGC 2865, are unique in that they provide evidence of recent accretion with gas and collisionless stars showing clear association, though the displacement suggests the presence of significant gas-dynamical interaction.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE STRUCTURE AND LINEAR POLARIZATION OF THE KILOPARSEC-SCALE JET OF THE QUASAR 3C 345

Deep Very Large Array imaging of the quasar 3C 345 at 4.86 and 8.44 GHz has been used to study the structure and linear polarization of its radio jet on scales ranging from 2 to 30 kpc. There is a 7-8 Jy unresolved core with spectral index {alpha} {approx_equal} -0.24 (I{sub {nu}}{proportional_to}{nu}{sup {alpha}}). The jet (typical intensity 15 mJy beam{sup -1}) consists of a 2.''5 straight section containing two knots, and two additional non-co-linear knots at the end. The jet's total projected length is about 27 kpc. The spectral index of the jet varies over -1.1 {approx}< {alpha} {approx}< -0.5. The jet diverges with a semi-opening angle of about 9 Degree-Sign , and is nearly constant in integrated brightness over its length. A faint feature northeast of the core does not appear to be a true counter-jet, but rather an extended lobe of this FR-II radio source seen in projection. The absence of a counter-jet is sufficient to place modest constraints on the speed of the jet on these scales, requiring {beta} {approx}> 0.5. Despite the indication of jet precession in the total intensity structure, the polarization images suggest instead a jet re-directed at least twice by collisions with the external medium. Surprisingly, the electric vector position angles in the main body of the jet are neither longitudinal nor transverse, but make an angle of about 55 Degree-Sign with the jet axis in the middle while along the edges the vectors are transverse, suggesting a helical magnetic field. There is no significant Faraday rotation in the source, so that is not the cause of the twist. The fractional polarization in the jet averages 25% and is higher at the edges. In a companion paper, Roberts and Wardle show that differential Doppler boosting in a diverging relativistic velocity field can explain the electric vector pattern in the jet.

79 ASTRONOMY AND ASTROPHYSICS↗