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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Metal/Ion Interactions Induced p–i–n Junction in Methylammonium Lead Triiodide Perovskite Single Crystals

Hybrid perovskites, as emerging multifunctional semiconductors, have demonstrated dual electronic/ionic conduction properties. Here, we report a metal/ion interaction induced p-i-n junction across slightly n-type doped MAPbI 3 single crystals with Au/MAPbI 3 /Ag configuration based on interface dependent Seebeck effect, Hall effect and time-of-flight secondary ion mass spectrometry analysis. The organic cations (MA + ) interact with Au atoms, forming positively charged coordination complexes at Au/MAPbI 3 interface, whereas iodine anions (I – ) can react with Ag contacts, leading to interfacial ionic polarization. Such metal/ion interactions establish a p-doped region near the Au/MAPbI 3 interface due to the formation of MA + vacancies, and an n-doped region near the Ag/MAPbI 3 interface due to formation of I – vacancies, consequently forming a p-i-n junction across the crystal in Au/MAPbI 3 /Ag configuration. Therefore, the metal/ion interaction plays a role in determining the surface electronic structure and semiconducting properties of hybrid perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Comprehensive demonstration of spin Hall Hanle effects in epitaxial Pt thin films

In this work, we demonstrate a nonlinear Hall effect due to the boundary spin accumulation in Pt films grown on Al 2 O 3 substrates. This Hall effect and the previously demonstrated Hanle magnetoresistance provide a complete picture of the spin-precession control of the spin and charge transport at the boundary of a spin-orbit coupled material, which we refer to as spin Hall Hanle effects (SHHE). We also show that the SHHE can be employed to measure the spin diffusion length, the spin Hall angle, and the spin relaxation time of heavy metal without the need of magnetic interface or the input from other measurements. The comprehensive demonstration of SHHE in such a simple system suggests they may be ubiquitous and needs to be considered for unraveling the spin and charge transport in more complex thin-film structures of spin-orbit coupled materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

X-ray spectroscopy of current-induced spin-orbit torques and spin accumulation in Pt / 3 d -transition-metal bilayers

An electric current flowing in Pt, a material with strong spin-orbit coupling, leads to spins accumulating at the interfaces by virtue of the spin Hall effect and interfacial charge-spin conversion. We measure the influence of these interfacial magnetic moments onto adjacent 3$d$ transition-metal layers by x-ray absorption spectroscopy and x-ray magnetic circular dichroism in a quantitative and element-selective way, with sensitivity below 10 -5 $_{μB}$ per atom. In Pt(6 nm)/Co(2.5 nm), the accumulated spins cause a deviation of the Co magnetization direction, which corresponds to an effective spin Hall angle of 0.08. The spin and orbital magnetic moments of Co are affected in equal proportion by the absorption of the spin current, showing that the transfer of orbital momentum from the recently predicted orbital Hall effect is either below our detection limit, or not directed to the 3$d$ states of Co. For Pt/NM (NM = Ti, Cr, Cu), we find upper limits for the amount of injected spins corresponding to about 3 × 10 -6 $_{μB}$ per atom.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Recent progress in MnBi2 n Te3 n +1 intrinsic magnetic topological insulators: crystal growth, magnetism and chemical disorder

ABSTRACT The search for magnetic topological materials has been at the forefront of condensed matter research for their potential to host exotic states such as axion insulators, magnetic Weyl semimetals, Chern insulators, etc. To date, the MnBi2nTe3n+1 family is the only group of materials showcasing van der Waals-layered structures, intrinsic magnetism and non-trivial band topology without trivial bands at the Fermi level. The interplay between magnetism and band topology in this family has led to the proposal of various topological phenomena, including the quantum anomalous Hall effect, quantum spin Hall effect and quantum magnetoelectric effect. Among these, the quantum anomalous Hall effect has been experimentally observed at record-high temperatures, highlighting the unprecedented potential of this family of materials in fundamental science and technological innovation. In this paper, we provide a comprehensive review of the research progress in this intrinsic magnetic topological insulator family, with a focus on single-crystal growth, characterization of chemical disorder, manipulation of magnetism through chemical substitution and external pressure, and important questions that remain to be conclusively answered.

36 MATERIALS SCIENCE↗
DOE OSTI2019

SOS: symmetry-operational similarity

Abstract Symmetry often governs condensed matter physics. The act of breaking symmetry spontaneously leads to phase transitions, and various observables or observable physical phenomena can be directly associated with broken symmetries. Examples include ferroelectric polarization, ferromagnetic magnetization, optical activities (including Faraday and magneto-optic Kerr rotations), second harmonic generation, photogalvanic effects, nonreciprocity, various Hall-effect-type transport properties, and multiferroicity. Herein, we propose that observable physical phenomena can occur when specimen constituents (i.e., lattice distortions or spin arrangements, in external fields or other environments) and measuring probes/quantities (i.e., propagating light, electrons, or other particles in various polarization states, including vortex beams of light and electrons, bulk polarization, or magnetization) share symmetry-operational similarity (SOS) in relation to broken symmetries. In addition, quasi-equilibrium electronic transport processes such as diode-type transport effects, linear or circular photogalvanic effects, Hall-effect-type transport properties ((planar) Hall, Ettingshausen, Nernst, thermal Hall, spin Hall, and spin Nernst effects) can be understood in terms of symmetry-operational systematics. The power of the SOS approach lies in providing simple and physically transparent views of otherwise unintuitive phenomena in complex materials. In turn, this approach can be leveraged to identify new materials that exhibit potentially desired properties as well as new phenomena in known materials.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Interface-driven spin-torque ferromagnetic resonance by Rashba coupling at the interface between nonmagnetic materials

The Rashba-Edelstein effect stems from the interaction between the electron's spin and its momentum induced by spin-orbit interaction at an interface or a surface. It was shown that the inverse Rashba-Edelstein effect can be used to convert a spin current into a charge current. Here, we demonstrate the reverse process of a charge-to spin-current conversion at a Bi/Ag Rashba interface. We show that this interface-driven spin current can drive an adjacent ferromagnet to resonance. We employ a spin-torque ferromagnetic resonance excitation/detection scheme which was developed originally for a bulk spin-orbital effect, the spin Hall effect. In our experiment, the direct Rashba-Edelstein effect generates an oscillating spin current from an alternating charge current driving the magnetization precession in a neighboring permalloy (Py, Ni 80 Fe 20 ) layer. As a result, electrical detection of the magnetization dynamics is achieved by a rectificationmechanism of the time dependent multilayer resistance arising from the anisotropic magnetoresistance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Optical properties of amorphous and crystalline Sb-doped SnO{sub 2} thin films studied with spectroscopic ellipsometry: Optical gap energy and effective mass

We investigated the optical properties of amorphous and crystalline antimony (Sb)-doped tin dioxide (SnO{sub 2}) thin films grown using the co-sputtering deposition method at room temperature. We used undoped and Sb-doped (8 wt. %) SnO{sub 2} targets. Varying the relative power ratio of the two targets, we controlled the Sb-composition of the SnO{sub 2}:Sb thin films up to 2.3 at. % of Sb contents. Through annealing, the as-grown amorphous SnO{sub 2}:Sb thin films were transformed to crystalline thin films. Dielectric functions were obtained from the measured ellipsometry angles, Ψ and Δ, using the Drude and parametric optical constant models. We determined the absorption coefficients and optical gap energies of the SnO{sub 2}:Sb thin films from the dielectric functions. We found increasing optical gap energy with increasing Sb composition. Increases in the Drude tail amplitudes, a signature of free carrier concentrations, were found in annealed, crystalline thin films with increasing Sb composition. The increase in the optical gap energy with increasing Sb composition was mainly attributed to the Burstein-Moss effect. Using Hall effect measurements, we obtained Hall carrier concentrations (N{sub Hall}) and electron Hall mobilities (μ{sub Hall}). The carrier concentrations and mobilities increased from 2.6 × 10{sup 19 }cm{sup −3} and 1.0 cm{sup 2}/(V s) to 2.0 × 10{sup 20 }cm{sup −1} and 7.2 cm{sup 2}/(V s), respectively, with increasing Sb contents. This result suggests that the nominally undoped SnO{sub 2} films are unintentionally n-type doped. Assuming that the N{sub Hall} and optical carrier concentrations (N{sub opt}) were the same, we obtained the effective masses of the SnO{sub 2}:Sb thin films with increasing Sb compositions. The effective masses of the SnO{sub 2}:Sb thin films increased from 0.245 m{sub 0} to 0.4 m{sub 0} with increasing Sb doping contents, and the nonparabolicity of the conduction band was estimated. We discussed the relation between the optical (μ{sub opt}) and Hall (μ{sub Hall}) mobilities as a function of Sb contents and grain sizes.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Physical properties of intergrowth compound Eu 2 CuZn 2 P 3

Here, the physical properties of single-crystalline Eu 2 ⁢CuZn 2 ⁢P 3 were inspected via thermodynamic, transport, and neutron diffraction measurements. Eu 2 ⁢ CuZn 2⁢ P 3 is composed of EuCuP and EuZn 2 ⁢ P 2 motifs stacked in a one-to-one ratio. The magnetic response of Eu 2 ⁢ CuZn 2 ⁢ P 3 is similar to that of EuZn 2 ⁢ P 2 in its A-type antiferromagnetic (semiconducting) state. A Néel temperature of T N = 40.3K is obtained from the specific heat capacity. Single-crystal neutron diffraction reveals a (001) magnetic propagation vector, with primarily in-plane moments coupled along [001] in an up-up-down-down pattern. This spin structure retains the ferromagnetic EuCuP motifs and antiferromagnetic coupling across the EuZn 2 ⁢P 2 motifs. The electrical resistivity is characterized by metallic behavior above 100 K, an increase in ρ upon cooling below ≈ 75K, and a large negative magnetoresistance below T N . First principles calculations evidence a narrow band gap for antiferromagnetic ordering and semimetallic behavior for the ferromagnetic state. This is consistent with the observed effect of magnetic field on the electrical resistivity. Hall effect measurements reveal a field-induced, negative anomalous Hall effect that increases on cooling down to 2 K. Also, an unconventional contribution to the Hall effect dominates the low-field Hall signal, particularly near T N , and is similar in appearance to a topological Hall effect. However, further work is necessary to understand if any of the transport properties have topological origins or if magnetism-induced modifications to the Fermi surface induce these unusual Hall effect signals in this and related materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

"Hall" transport of liquid crystal solitons in Couette flow

Topology establishes a unifying framework for a diverse range of scientific areas including particle physics, cosmology, and condensed matter physics. One of the most fascinating manifestations of topology in the context of condensed matter is the topological Hall effect, and its relative: the Skyrmion Hall effect. Skyrmions are stable vortex-like spin configurations in certain chiral magnets, and when subject to external electric currents can drift in the transverse direction to the current. These quasi-particles are characterised by a conserved topological charge which in the Skyrmion Hall effect plays the role of electric charges in the ordinary Hall effect. Recently, it has been shown that liquid crystals endowed with chiral properties serve as an ideal testbed for the fundamental investigation of topological solitons, including their two- and three-dimensional realisations. Here, we show experimentally and numerically that three-dimensional solitons aka "torons" exhibit a Hall-like effect when driven by shear flows: the torons are deflected in the direction perpendicular to the shear plane. The experimental results are rationalised in terms of the dynamic Ericksen-Leslie equations, which predict the emergence of the transverse component of the net mass flow, the magnitude of which scales as the 3rd power of the shear rate. The perturbation analysis highlights an interplay of the viscous and chiral elastic torques as the mechanism for the emergence of net transverse currents. Numerical simulations demonstrate, however, that torons are not merely dragged by the flow but move with their own transverse speed, much larger than the average flow velocity in the transverse direction. Our findings may enable responsive microfluidic applications relying on soft topological solitons.

FOS: Physical sciences↗
DOE OSTI2013

Study of the effects of guide field on Hall reconnection

The results from guide field studies on the Magnetic Reconnection Experiment (MRX) are compared with results from Hall magnetohydrodynamic (HMHD) reconnection simulation with guide field. The quadrupole field, a signature of two-fluid reconnection at zero guide field, is modified by the presence of a finite guide field in a manner consistent with HMHD simulation. The modified Hall current profile contains reduced electron flows in the reconnection plane, which quantitatively explains the observed reduction of the reconnection rate. The present results are consistent with the hypothesis that the local reconnection dynamics is dominated by Hall effects in the collisionless regime of the MRX plasmas. While very good agreement is seen between experiment and simulations, we note that an important global feature of the experiments, a compression of the guide field by the reconnecting plasma, is not represented in the simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

ON SPECTRAL BREAKS IN THE POWER SPECTRA OF MAGNETIC FLUCTUATIONS IN FAST SOLAR WIND BETWEEN 0.3 AND 0.9 AU

We analyze the radial variation of the power spectra of the magnetic field from 0.3 to about 0.9 AU, using Helios 2 spacecraft measurements in the fast solar wind. The time resolution of the magnetic field data allows us to study the power spectra up to 2 Hz. Generally, the corresponding spectral break frequency f{sub b} and the Doppler-shifted frequencies, which are related to the proton gyroradius and inertial scales, are close to a frequency f of about 0.5 Hz at a distance of 1 AU from the Sun. However, studying the radial evolution of the power spectra offers us the possibility to distinguish between those scales. Recent Ulysses observations show that, while the proton scales vary, f{sub b} stays nearly constant with the heliocentric distance R. In our study we confirm that f{sub b} varies within a small interval of [0.2, 0.4] Hz only, as R varies from 0.3 to 0.9 AU. Moreover, if we assume parallel propagating fluctuations (with respect to the solar wind flow or background magnetic field), we can show that none of the proton scales are coincident with the break scale. If, however, we take into account the two-dimensional nature of the turbulent fluctuations, then we can show that the spatial scale corresponding to f{sub b} (R) does follow the proton inertial scale, {lambda}{sub p}(R), but not the proton gyroradius scale, {rho}{sub p}(R), as a function of heliocentric distance. These observations indicate that the spectral break at the proton inertial scale might be related to the Hall effect, or be controlled by the ion-cyclotron damping of obliquely propagating fluctuations or the formation of current sheets scaling like {lambda}{sub p}, which could be responsible for ion heating through magnetic reconnection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Electronic Structure and Electronic Properties of PtSn{sub 4} Single Crystal

A topological semimetal PtSn{sub 4} single crystal is grown and the following properties are studied: its electrical resistivity in the temperature range from 4.2 to 300 K, galvanomagnetic properties at temperatures from 4.2 to 80 K and in magnetic fields of up to 100 kOe, and optical properties at room temperature. Theoretical calculations of the electronic structure are performed. It is shown that the residual resistivity is rather small: ρ{sub 0} = 0.47 μΩ cm, which is characteristic of a “good” metal. The ρ(T) dependence is of the metallic type, increasing monotonically with temperature. Analysis of the temperature dependences of the magnetoresistivity suggests that the Fermi surface of the PtSn{sub 4} compound may contain closed sheets. Studies of the Hall effect and the estimates made in the single-band model allowed us to conclude that the predominant type of current carriers are holes with concentration n = 6.8 × 10{sup 21} cm{sup –3} and mobility μ ≈ 1950 cm{sup 2}/(V s) at T = 4.2 K. It is shown that the optical properties of PtSn{sub 4} have features characteristic of “bad” metals. The calculation of the electronic structure of PtSn{sub 4} showed that, in general, this compound has a structure characteristic of metallic systems with a sufficiently large number of electronic states at the Fermi level, which is consistent with the experimental results on the electronic transport and optical properties of the PtSn{sub 4} single crystal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Sheath oscillation characteristics and effect on near-wall conduction in a krypton Hall thruster

Despite its affordability, the krypton Hall-effect thruster in applications always had problems in regard to performance. The reason for this degradation is studied from the perspective of the near-wall conductivity of electrons. Using the particle-in-cell method, the sheath oscillation characteristics and its effect on near-wall conduction are compared in the krypton and xenon Hall-effect thrusters both with wall material composed of BNSiO{sub 2}. Comparing these two thrusters, the sheath in the krypton-plasma thruster will oscillate at low electron temperatures. The near-wall conduction current is only produced by collisions between electrons and wall, thereby causing a deficiency in the channel current. The sheath displays spatial oscillations only at high electron temperature; electrons are then reflected to produce the non-oscillation conduction current needed for the krypton-plasma thruster. However, it is accompanied with intensified oscillations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Spin Hall effect-controlled magnetization dynamics in NiMnSb

We investigate the influence of a spin current generated from a platinum layer on the ferromagnetic resonance (FMR) properties of an adjacent ferromagnetic layer composed of the halfmetallic half-Heusler material NiMnSb. Spin Hall nano-oscillator devices are fabricated, and the technique of spin torque FMR is used to locally study the magnetic properties as in-plane anisotropies and resonance fields. A change in the FMR linewidth, in accordance with the additional spin torque produced by the spin Hall effect, is present for an applied dc current. For sufficiently large currents, this should yield auto-oscillations, which however are not achievable in the present device geometry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

SHEAR-DRIVEN INSTABILITIES IN HALL-MAGNETOHYDRODYNAMIC PLASMAS

The large-scale dynamics of plasmas is well described within the framework of magnetohydrodynamics (MHD). However, whenever the ion density of the plasma becomes sufficiently low, the Hall effect is likely to become important. The role of the Hall effect has been studied in several astrophysical plasma processes, such as magnetic reconnection, magnetic dynamo, MHD turbulence, or MHD instabilities. In particular, the development of small-scale instabilities is essential to understand the transport properties in a number of astrophysical plasmas. The magneto-rotational instability (MRI), which takes place in differentially rotating accretion disks embedded in relatively weak magnetic fields, is just one example. The influence of the large-scale velocity flows on small-scale instabilities is often approximated by a linear shear flow. In this paper, we quantitatively study the role of the Hall effect on plasmas embedded in large-scale shear flows. More precisely, we show that an instability develops when the Hall effect is present, which we therefore term as the Hall magneto-shear instability. As a particular case, we recover the so-called MRI and quantitatively assess the role of the Hall effect on its development and evolution.

79 ASTRONOMY AND ASTROPHYSICS↗