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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Magnetic scattering and spin-orbit coupling induced magnetoresistance in nonmagnetic heavy metal and magnetic insulator bilayer systems

Here, we report on the experimental study of the angular dependent magnetoresistance (MR) of heavy metal/ferromagnetic insulator bilayer structures. Through altering the relative composition in heavy metal Pt δ Ta 1–δ alloy, we continuously tune its spin Hall angle from positive, crossing zero, and to negative and study its impact on the MR. Most notably, both spin Hall effect and MR disappear simultaneously in Pt 0.32 Ta 0.68 (3 nm)/YIG when the effective spin Hall angle vanishes, evidencing the essential role of spin-orbit coupling in heavy metal for the MR. By introducing Fe impurities, we further identify that magnetic scattering is also essential to induce the MR in Pt/Fe-doped SiO 2 at large magnetic field, where the MR ratio increases monotonically with doping level.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

High Thermal Conductivity Resin Systems for High Energy Physics Magnets

In Nb3Sn superconducting magnets, the cable and insulation system dominate the behavior of a completed magnet, with contributions to the mechanical behavior from the stiff, brittle components of the superconductor, the soft annealed copper stabilizer, and the properties of the composite insulation system. As these components are closely integrated on a small scale, it is of value to explore the properties of the entire system at a larger scale, to enable practical magnet design. Subscale composite testing (Stack Testing) has been used extensively to study the bulk material properties of the magnet composite structure. Small samples that mimic the fabrication process of magnets are fabricated and tested to qualify and characterize magnet insulation systems for use in future magnet projects as well as to better inform magnet designers about means for assembly and general handling processes. Subscale composite samples will be fabricated and characterized using various novel resins to work to improve magnet performance. New resin systems will be screened to allow for down selection to one or more highly promising resin systems. The work performed under this agreement at Fermilab will feed via CTD into the fabrication of subscale magnets at Lawrence Berkeley National Laboratory (LBNL) for verification of magnet performance.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

SolCalc: A Suite for the Calculation and the Display of Magnetic Fields Generated by Solenoid Systems

SolCalc is a software suite that computes and displays magnetic fields generated by a three dimensional (3D) solenoid system. Examples of such systems are the Mu2e magnet system and Helical Solenoids for muon cooling systems. SolCalc was originally coded in Matlab, and later upgraded to a compiled version (called MEX) to improve solving speed. Matlab was chosen because its graphical capabilities represent an attractive feature over other computer languages. Solenoid geometries can be created using any text editor or spread sheets and can be displayed dynamically in 3D. Fields are computed from any given list of coordinates. The field distribution on the surfaces of the coils can be displayed as well. SolCalc was benchmarked against a well-known commercial software for speed and accuracy and the results compared favorably.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Method for improved voltage determination for pulsed power systems utilizing a magnetically insulated transmission line

Because the voltage is difficult to measure in a magnetically insulated transmission line (MITL), measurement of the currents flowing in the cathode and anode are often used with MITL theory to estimate the voltage in a given experiment. However, that estimate contains a space charge correction term whose magnitude depends on what is referred to as the g factor that describes the distribution of charge and current in the electron flow layer in the MITL. Typically, g is on the order of unity but the accuracy of the voltage estimate depends on its actual value. While the space charge correction term is small when the MITL flow is strongly insulated, it is particularly important near self-limited MITL flow. System parameters that affect the distribution of electron flow are studied here at self-limited flow in order to illustrate this matter and develop a methodology to improve the voltage determination.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Stabilization and control of topological magnetic solitons via magnetic nanopatterning of exchange bias systems

Stabilizing and manipulating topological magnetic quasiparticles in thin films is of great interest for potential applications in data storage and information processing. Here, we present a strategy for stabilizing magnetic vortices and Bloch lines with controlled position, vorticity, and chirality in a continuous exchange bias system. By tailoring vectorially the unidirectional anisotropy of the system at the nanoscale, via thermally assisted magnetic scanning probe lithography, we show experimentally and via micromagnetic simulations the non-volatile creation of vortex-antivortex pairs. In addition, we demonstrate the deterministic stabilization of cross and circular Bloch lines within patterned Néel magnetic domain walls. This work enables the implementation of complex functionalities based on the control of tailored topological spin-textures in spintronic and magnonic nanodevices.

Magnetic ordering↗
DOE OSTI2018

Rapid Assessment of the Ce-Co-Fe-Cu System for Permanent Magnetic Applications

Here, this work focuses on the rapid synthesis and characterization of quaternary Ce(CoFeCu) 5 alloy libraries to assess their potential viability as permanent magnets. Arrays of bulk specimens with controlled compositions were synthesized via laser engineered net shaping (LENS) by feeding different ratios of alloy powders into a melt pool created by a laser. Based on the assessment of the magnetic properties of the LENS printed samples, arc-melted and cast ingots were prepared with varying Fe (5–20 at.%) and Co (60–45 at.%) compositions while maintaining constant Ce (16 at.%) and Cu (19 at.%) content. The evolution of the microstructure and phases with varying chemical compositions and their dependence on magnetic properties are analyzed in as-cast and heat-treated samples. In both the LENS printed and cast samples, we find the best magnetic properties correspond to a predominantly single-phase Ce(CoFeCu) 5 microstructure in which high coercivity ( H c > 10 kOe) can be achieved without any microstructural refinement.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Reconfigurable Pinwheel Artificial-Spin-Ice and Superconductor Hybrid Device

The ability to control the potential landscape in a medium of interacting particles could lead to intriguing collective behavior and innovative functionalities. In this work, we utilize spatially reconfigurable magnetic potentials of a pinwheel artificial-spin-ice (ASI) structure to tailor the motion of superconducting vortices. The reconstituted chain structures of the magnetic charges in the pinwheel ASI and the strong interaction between magnetic charges and superconducting vortices allow significant modification of the transport properties of the underlying superconducting thin film, resulting in a reprogrammable resistance state that enables a reversible and switchable vortex Hall effect. Our results highlight an effective and simple method of using ASI as an in situ reconfigurable nanoscale energy landscape to design reprogrammable superconducting electronics, which could also be applied to the in situ control of properties and functionalities in other magnetic particle systems, such as magnetic skyrmions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Instability growth for magnetized liner inertial fusion seeded by electro-thermal, electro-choric, and material strength effects

A critical limitation of magnetically imploded systems such as magnetized liner inertial fusion (MagLIF) [Slutz et al., Phys. Plasmas 17, 056303 (2010)] is the magneto-Rayleigh-Taylor (MRT) instability which primarily disrupts the outer surface of the liner. MagLIF-relevant experiments have showed large amplitude multi-mode MRT instability growth growing from surface roughness [McBride et al., Phys. Rev. Lett. 109, 135004 (2012)], which is only reproduced by 3D simulations using our MHD code Gorgon when an artificially azimuthally correlated initialisation is added. We have shown that the missing azimuthal correlation could be provided by a combination of the electro-thermal instability (ETI) and an “electro-choric” instability (ECI); describing, respectively, the tendency of current to correlate azimuthally early in time due to temperature dependent Ohmic heating; and an amplification of the ETI driven by density dependent resistivity around vapourisation. We developed and implemented a material strength model in Gorgon to improve simulation of the solid phase of liner implosions which, when applied to simulations exhibiting the ETI and ECI, gave a significant increase in wavelength and amplitude. Full circumference simulations of the MRT instability provided a significant improvement on previous randomly initialised results and approached agreement with experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures

We review some of the significant contributions to the field of strongly correlated materials and complex magnets, arising from experiments performed at the Diamond Light Source (Harwell Science and Innovation Campus, Didcot, UK) during the first few years of operation (2007–2014). We provide a comprehensive overview of Diamond research on topological insulators, multiferroics, complex oxides and magnetic nanostructures. Several experiments on ultrafast dynamics, magnetic imaging, photoemission electron microscopy, soft X-ray holography and resonant magnetic hard and soft X-ray scattering are described.

Radaelli, P. G.↗
DOE OSTI2017

Formation of gapless Z{sub 2} spin liquid phase manganites in the (Sm{sub 1–y}Gd{sub y}){sub 0.55}Sr{sub 0.45}MnO{sub 3} system in zero magnetic field: Topological phase transitions to states with low and high density of 2D-vortex pairs induced by the magnetic field

The evolution of the ground state of the manganese spin ensemble in the (Sm{sub 1–y}Gd{sub y}){sub 0.55}Sr{sub 0.45}MnO{sub 3} in the case of isovalent substitution of rare-earth samarium ions with large radii with gadolinium ions with significantly smaller radii is studied. The measured temperature dependences of the ac magnetic susceptibility and the field dependences of the dc magnetizations are analyzed using the Heisenberg–Kitaev model describing the transition from the ordered spin state with classical isotropic AFM exchange to the frustrated spin state with quantum highly anisotropic FM exchange. A continuous transition from the 3D ferromagnetic state of manganese spins in the initial sample with y = 0 to zigzag AFM ordering of CE-type spins in ab planes for y = 0.5, coexisting in samples with y = 0.5, 0.6, and 0.7 at temperatures below T{sub N} ≅ 48.5 K with a disordered phase such as a quantum Griffiths phase is identified. As the gadolinium concentration further increases, the CE-type zigzag AFM structure is molten, which leads to the appearance of an unusual phase in Gd{sub 0.55}Sr{sub 0.45}MnO{sub 3} in the temperature range close to the absolute zero. This phase has characteristic features of a gapless Z{sub 2} quantum spin liquid in zero external magnetic field. The step changes in the magnetization isotherms measured at 4.2 K in the field range of ±75 kOe are explained by quantum phase transitions of the Z{sub 2} spin liquid to a phase with topological order in weak magnetic fields and a polarized phase in strong fields. The significant difference between critical fields and magnetization jumps in isotherms indicates the existence of hysteretic phenomena in quantum spin liquid magnetization–demagnetization processes caused by the difference between localization–delocalization of 2D vortex pairs induced by a magnetic field in a quantum spin liquid with disorder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Competition between domain walls and the reverse magnetization in the magnetic relaxation of a Pt/Co/Ir/Co/Pt spin switcher

A multilayer Pt/Co/Ir/Co/Pt/GaAs heterostructures demonstrates a long term (to several hours) magnetic relaxation between two stable states of the magnetization of the system. The magnetization reversal of the heterostructure layers occurs both due to the formation of nuclei of the reverse magnetization domains and as a result of their further growth by means of motion of domain walls. The competition between two these processes provides a nonexponential character of the magnetic relaxation. At 300 K, the contributions of these processes to the relaxation are commensurable, while, at temperatures lower than 200 K, the contribution of the nucleation is suppressed and the magnetic relaxation occurs as a result of motion of the domain walls.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗