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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Applied magnetic field synthesis and processing of iron nitride magnetic materials

Techniques are disclosed concerning applied magnetic field synthesis and processing of iron nitride magnetic materials. Some methods concern casting a material including iron in the presence of an applied magnetic field to form a workpiece including at least one ironbased phase domain including uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T). Also disclosed are workpieces made by such methods, apparatus for making such workpieces and bulk materials made by such methods.

Wang, Jian-Ping↗
DOE OSTI2021

Manipulation of Magnetic Skyrmion in a 2D van der Waals Heterostructure via Both Electric and Magnetic Fields

As a promising candidate for the much-desired low power consumption spintronic devices, 2D magnetic van der Waals material also provides a versatile platform for the design and control of topological spin textures. In this work on WTe 2 /CrCl 3 bilayer van der Waals heterostructures, a complete Néel-type skyrmion–bimeron–ferromagnet phase transition is demonstrated, accompanied by the evolution of the topological number. This cyclic transition, mediated by a perpendicular magnetic field, is largely driven by the competition between the out-of-plane magnetocrystalline anisotropy and magnetic dipole–dipole interaction. In the presence of a driving current, the Néel-type skyrmion gains a higher velocity yet larger skyrmion Hall angle, in comparison to the bimeron. By incorporating a ferroelectric CuInP 2 S 6 monolayer as a substrate, writing and erasing of skyrmions may be regulated using a ferroelectric polarization. Here this work sheds light on a novel approach to the design and control of magnetic skyrmions on 2D van der Waals materials.

multiferroic↗
DOE OSTI2018

161 Dy Time-Domain Synchrotron Mössbauer Spectroscopy for Investigating Single-Molecule Magnets Incorporating Dy Ions [ 161 Dy time-domain synchrotron Mössbauer spectroscopy as a new way forward for investigating single molecule magnets incorporating Dy ions]

Time–domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of 161 Dy has been used to investigate the magnetic properties of a Dy III –based single–molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy 3 PO) 2 (H 2 O) 5 ]Br 3 •2 (Cy 3 PO)•2 H 2 O•2 EtOH is with B 0 =582.3(5) T significantly larger than that of the free–ion Dy III with a 6 H 15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the Dy III ion. Furthermore this study demonstrates that 161 Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy–containing compounds.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Low-temperature magnetization dynamics of magnetic molecular solids in a swept field

The swept-field experiments on magnetic molecular solids such as Fe{sub 8} are studied using Monte Carlo simulations, and a kinetic equation developed to understand collective magnetization phenomena in such solids, where the collective aspects arise from dipole–dipole interactions between different molecules. Because of these interactions, the classic Landau–Zener–Stückelberg theory proves inadequate, as does another widely used model constructed by Kayanuma. It is found that the simulations provide a quantitatively accurate account of the experiments. The kinetic equation provides a similarly accurate account except at very low sweep velocities, where it fails modestly. This failure is attributed to the neglect of short-range correlations between the dipolar magnetic fields seen by the molecular spins. The simulations and the kinetic equation both provide a good understanding of the distribution of these dipolar fields, although analytic expressions for the final magnetization remain elusive.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

On the missing magnetic flux and topological effects of a screw dislocation on a charged particle in an inhomogeneous magnetic field

Highlights: • Aharonov–Bohm-type effect associated with the missing magnetic flux. • Persistent currents associated with the missing magnetic flux. • Aharonov–Bohm-type effect associated with the screw dislocation topology. We study the interaction of an electron/hole with inhomogeneous magnetic field in the presence of a screw dislocation. We consider the internal structure of the defect, i.e., we consider the core that gives rise to a finite size to the defect. In addition, we assume that this core determines a forbidden region for the electron/hole. Then, we solve the Schrödinger equation and show that an Aharonov–Bohm-type effect arises from the influence of the topological defect and the missing magnetic flux on the eigenvalues of energy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Magnetic-field-induced synthesis of Fe{sub 3}O{sub 4} nanorods by a gas–liquid interfacial process: Microstructure control, magnetic and photocatalytic properties

Highlights: • Fe{sub 3}O{sub 4} nanorods were synthesized via a MFI gas–liquid interfacial route. • The morphology of the Fe{sub 3}O{sub 4} nanoparticle can be changed during its growth process. • MF render Fe{sub 3}O{sub 4} nanorods higher degree of crystallinity and better magnetic property. - Abstract: In this paper, we designed a magnetic field (MF) induced gas–liquid interface route to synthesize magnetic Fe{sub 3}O{sub 4} nanorods (NRs). The results showed that the MF can significantly affect the morphology of the particles. In this original method, only relatively inexpensive and environmental chemicals were used. The structure and morphology of the Fe{sub 3}O{sub 4} NRs were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry technique. The crystal growth mechanisms in the magnetic field induced process were expounded in detail. The as-synthesized Fe{sub 3}O{sub 4} NRs were successfully used as a catalytic carrier for the photo degradation of phenol.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Self-Consistent Field Methods for Excited States in Strong Magnetic Fields: A Comparison Between Energy - and Variance-based Approaches

An efficient implementation of geometrical derivatives at the Hartree–Fock (HF) and current-density functional theory (CDFT) levels is presented for the study of molecular structure in strong magnetic fields. The required integral derivatives are constructed using a hybrid McMurchie–Davidson and Rys quadrature approach, which combines the amenability of the former to the evaluation of derivative integrals with the efficiency of the latter for basis sets with high angular momentum. In addition to its application to evaluating derivatives of four-center integrals, this approach is also applied to gradients using the resolution-of-the-identity approximation, enabling efficient optimization of molecular structure for many-electron systems under a strong magnetic field. The CDFT contributions have been implemented for a wide range of density functionals up to and including the meta-GGA level with current-density dependent contributions and (range-separated) hybrids for the first time. Illustrative applications are presented to the OH and benzene molecules, revealing the rich and complex chemistry induced by the presence of an external magnetic field. Challenges for geometry optimization in strong fields are highlighted, along with the requirement for careful analysis of the resulting electronic structure at each stationary point. The importance of correlation effects is examined by comparison of results at the HF and CDFT levels. The present implementation of molecular gradients at the CDFT level provides a cost-effective approach to the study of molecular structure under strong magnetic fields, opening up many new possibilities for the study of chemistry in this regime.

Comparison↗
DOE OSTI2023

Ultra-Low Viscosity and High Magnetic Susceptibility Magnetic Ionic Liquids Featuring Functionalized Diglycolic Acid Ester Rare-Earth and Transition Metal Chelates

Magnetic ionic liquids (MILs) comprise a subcategory of ionic liquids (ILs) and contain a paramagnetic metal center allowing them to be readily manipulated by an external magnetic field. While MILs are popularly employed as solvents in catalysis, separations, and organic synthesis, most low viscosity combinations possess a hydrophilic character that limits their use in aqueous matrices. To date, no study has reported the synthesis and characterization of hydrophobic MILs with viscosities similar to those of hydrophilic MILs and organic solvents while simultaneously exhibiting enhanced magnetic and thermal properties. In this study, diglycolic acid esters are employed as ligands to chelate with paramagnetic metals to produce cations that are paired with metal chelates composed of hexafluoroacetylacetonate ligands to form MILs incorporating multiple metal centers in the cation and anion. Viscosity values below 31.6 cP were obtained for these solvents, the lowest ever reported for hydrophobic MILs. Solubilities in nonpolar solvents such as benzene were observed to be as high as 50% (w/v) MIL-to-solvent ratio while being insoluble in water at concentrations as low as 0.01% (w/v). Effective paramagnetic moment values for these solvents ranged from 5.33 to 15.56 Bohr magnetons (μB), with mixed metal MILs containing multiple lanthanides in the anion generally offering higher magnetic susceptibilities. MILs composed of ligands containing octyl substituents were found to possess thermal stabilities up to 190 °C. The synthetic strategies explored in this study exploit the highly tunable nature of the employed cation and anion pairs to design versatile ultra-low viscosity magnetoactive solvents that possess tremendous potential and applicability in liquid–liquid separation systems, catalysis, and microfluidics where the mechanical movement of the solvent can be easily facilitated using electromagnets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Studies on the effect of the axial magnetic field on the x-ray bremsstrahlung in a 2.45 GHz permanent magnet microwave ion source

A compact microwave ion source has been designed and developed for operation at a frequency of 2.45 GHz. The axial magnetic field is based on two permanent magnet rings, operating in the “off-resonance” mode and is tunable by moving the permanent magnets. In order to understand the electron energy distribution function, x-ray bremsstrahlung has been measured in the axial direction. Simulation studies on the x-ray bremsstrahlung have been carried out to compare with the experimental results. The effect of the axial magnetic field with respect to the microwave launching position and the position of the extraction electrode on the x-ray bremsstrahlung have been studied.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Do dispersive waves play a role in collisionless magnetic reconnection?

Using fully kinetic simulations, we demonstrate that the properly normalized reconnection rate is fast ∼0.1 for guide fields up to 80× larger than the reconnecting field and is insensitive to both the system size and the ion to electron mass ratio. These results challenge conventional explanations of reconnection based on fast dispersive waves, which are completely absent for sufficiently strong guide fields. In this regime, the thickness of the diffusion layer is set predominantly by the electron inertial length with an inner sublayer that is controlled by finite gyro-radius effects. As the Alfvén velocity becomes relativistic for very strong guide fields, the displacement current becomes important and strong deviations from charge neutrality occur, resulting in the build-up of intense electric fields which absorb a portion of the magnetic energy release. Over longer time scales, secondary magnetic islands are generated near the active x-line while an electron inertial scale Kelvin-Helmholtz instability is driven within the outflow. These secondary instabilities give rise to time variations in the reconnection rate but do not alter the average value.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Thermally assisted magnetic switching of a single perpendicularly magnetized layer induced by an in-plane current

We report that by heating samples the critical current density for magnetization reversal (J{sub c}) in a single perpendicularly magnetized layer can be decreased from 2.6 × 10{sup 7 }A/cm{sup 2} to about 1 × 10{sup 6 }A/cm{sup 2} for a temperature increase of 143 K. The nonlinear dependence of J{sub c} on the perpendicular anisotropy field indicates that the coherent magnetic switching model cannot fully explain the current-induced perpendicular switching. By considering the current-induced domain nucleation and expansion during switching, we conclude that J{sub c} also depends on current-induced domain behavior. Moreover, by reversing the heat flow direction, we demonstrate that the thermal related spin transfer torques have little influence on the thermally assisted magnetic switching.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Magnetic diagnostics for equilibrium reconstructions with eddy currents on the lithium tokamak experiment

The Lithium Tokamak eXperiment is a spherical tokamak with a close-fitting low-recycling wall composed of thin lithium layers evaporated onto a stainless steel-lined copper shell. Long-lived non-axisymmetric eddy currents are induced in the shell and vacuum vessel by transient plasma and coil currents and these eddy currents influence both the plasma and the magnetic diagnostic signals that are used as constraints for equilibrium reconstruction. A newly installed set of re-entrant magnetic diagnostics and internal saddle flux loops, compatible with high-temperatures and lithium environments, is discussed. Details of the axisymmetric (2D) and non-axisymmetric (3D) treatments of the eddy currents and the equilibrium reconstruction are presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Interface magnetism of Co{sub 2}FeGe Heusler alloy layers and magnetoresistance of Co{sub 2}FeGe/MgO/Fe magnetic tunnel junctions

The interface magnetism between Co{sub 2}FeGe Heusler alloy layers and MgO layers was investigated using {sup 57}Fe Mössbauer spectroscopy. Interface-sensitive samples, where the {sup 57}Fe isotope was used only for the interfacial atomic layer of the Co{sub 2}FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The {sup 57}Fe Mössbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co{sub 2}FeGe films in which the {sup 57}Fe isotope was distributed throughout the films. On the other hand, the tunnel magnetoresistance effect of magnetic tunnel junctions with Co{sub 2}FeGe layers as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Interface driven magnetic interactions in nanostructured thin films of iron nanocrystallites embedded in a copper matrix

We have fabricated thin films of iron nanocrystallites embedded in a copper matrix using a dual ion beam assisted deposition technique. A secondary End-Hall ion beam bombarded the iron atoms during deposition altering significantly the morphology of the films and allowing for control of the intermixing between iron and copper components. Cross-sectional transmission electron microscopy and x-ray reflectometry experiments indicated that the morphology of the films was that of iron nanocrystallites embedded in a copper matrix. Rietveld refinements of the diffraction pattern identified fcc-copper and amorphous iron. An increased amount of disorder was observed with a reduction in the amount of deposited iron from a 1:1 Fe:Cu ratio to 0.25:0.75 Fe:Cu ratio. Interfacial copper-iron alloys were identified by DC susceptibility experiments through their reduced T{sub C,Alloy} (370, 310, and 280 K) compared with that of bulk iron (∼1000 K). Element specific x-ray absorption and x-ray magnetic circular dichroism experiments were performed to identify the contributions to the magnetism from the iron and the copper-iron alloy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Diagnosing magnetized liner inertial fusion experiments on Z

Magnetized Liner Inertial Fusion experiments performed at Sandia's Z facility have demonstrated significant thermonuclear fusion neutron yields (∼10{sup 12} DD neutrons) from multi-keV deuterium plasmas inertially confined by slow (∼10 cm/μs), stable, cylindrical implosions. Effective magnetic confinement of charged fusion reactants and products is signaled by high secondary DT neutron yields above 10{sup 10}. Analysis of extensive power, imaging, and spectroscopic x-ray measurements provides a detailed picture of ∼3 keV temperatures, 0.3 g/cm{sup 3} densities, gradients, and mix in the fuel and liner over the 1–2 ns stagnation duration.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Development of a vector-tensor system to measure the absolute magnetic flux density and its gradient in magnetically shielded rooms

Several experiments in fundamental physics demand an environment of very low, homogeneous, and stable magnetic fields. For the magnetic characterization of such environments, we present a portable SQUID system that measures the absolute magnetic flux density vector and the gradient tensor. This vector-tensor system contains 13 integrated low-critical temperature (LTc) superconducting quantum interference devices (SQUIDs) inside a small cylindrical liquid helium Dewar with a height of 31 cm and 37 cm in diameter. The achievable resolution depends on the flux density of the field under investigation and its temporal drift. Inside a seven-layer mu-metal shield, an accuracy better than ±23 pT for the components of the static magnetic field vector and ±2 pT/cm for each of the nine components of the gradient tensor is reached by using the shifting method.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Negative spontaneous magnetization and semi-spin glass magnetic order in mixed spinel Co{sub 0.6}Zn{sub 0.4}Fe{sub 1.7}Mn{sub 0.3}O{sub 4}

In this paper, we establish the negative spontaneous magnetization in Mn and Zn substituted cobalt ferrite Co{sub 0.6}Zn{sub 0.4}Fe{sub 1.7}Mn{sub 0.3}O{sub 4} (CZFMO). It is suggested that the origin of negative spontaneous magnetization is due to the substitution of small sized Mn{sup +4} ions (compared to Fe{sup +3} ions) at the octahedral B site in compound Co{sub 0.6}Zn{sub 0.4} Fe{sub 2}O{sub 4}. The low value of Poisson's ratio ∼0.202 for this compound possibly contributes towards the easy distortion in the bond length and bond angle, causing increase in Fe-O bond distance/decrease in Fe-O-Fe bond angle with Mn substitution, leading to considerably weak Fe-O-Fe superexchange interaction at the octahedral B site. The neutron diffraction data clearly illustrated the significant reduction in ordered magnetic moment at the B site, with the resultant negative spontaneous magnetization (M = M{sub B} − M{sub A}) in this mixed spinel system. The spin disorder also gives rise to an interesting semi-spin glass behavior in CZFMO.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗