Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “MAGNESIUM 39”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Nuclear Data Sheets for A=39☆

Experimental nuclear structure data from various reactions and decays have been evaluated for all known nuclides of mass 39 (Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, Ti). Detailed evaluated nuclear structure information is presented for each reaction and decay and the best values combining all available data are recommended for level energies, half-lives, γ-ray energies and intensities, decay properties (energies, intensities and placement of radiations), and other spectroscopic data. The {sup 39}K, {sup 39}Ca and {sup 39}Ar are the most extensively studied nuclides; no excited states are known in {sup 39}Mg and {sup 39}Ti. This work supersedes the earlier full evaluation of A=39 by B. Singh and J. Cameron (2006Si02).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Advantages of Superconducting Device using 26 MgB2 Wire

Superconducting undulator (SCU) which can run at higher temperature than 4 Kelvin range has been anticipated for a long time. However, the performance of high-temperature superconductor (HTS) tapes have not improved over the last decade as the industry mostly concentrates on the cost reduction. Magnesium Diboride (MgB2) has a critical temperature of 39 K and the 1 st generation (1G) wire has been in production but it was not sufficient to be used in SCU. Recently the 2 nd generation (2G) wire has been developed. It is estimated to give a similar performance as NbTi wire at 20K. In this paper the advantages of a SCU with 2G MgB2 wire compared to a conventional SCU with NbTi or Nb3Sn3 wire.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Wafer-Scale MgB 2 Superconducting Devices

Progress in superconducting device and detector technologies over the past decade has realized practical applications in quantum computers, detectors for far-infrared telescopes, and optical communications. Superconducting thin-film materials, however, have remained largely unchanged, with aluminum still being the material of choice for superconducting qubits and niobium compounds for high-frequency/high kinetic inductance devices. Magnesium diboride (MgB 2 ), known for its highest transition temperature (T c = 39 K) among metallic superconductors, is a viable material for elevated temperature and higher frequency superconducting devices moving toward THz frequencies. However, difficulty in synthesizing wafer-scale thin films has prevented implementation of MgB 2 devices into the application base of superconducting electronics. Here, we report ultrasmooth (<0.5 nm root-mean-square roughness) and uniform MgB 2 thin (<100 nm) films over 100 mm in diameter and present prototype devices fabricated with these films demonstrating key superconducting properties including an internal quality factor over 10 4 at 4.5 K and high tunable kinetic inductance in the order of tens of pH/sq in a 40 nm thick film. This advancement will enable development of elevated temperature, high-frequency superconducting quantum circuits, and devices.

Boron↗
DOE OSTI2016

Geometries, Binding Energies, Ionization Potentials, and Electron Affinities of Metal Clusters: Mg n 0, ± 1 , n = 1–7

Equilibrium geometries, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for neutral and singly charged magnesium clusters, Mg n 0, ± 1 , n = 1–7, have been computed using 39 exchange-correlation (XC) functionals in Kohn–Sham density functional theory and several coupled-cluster methods with single, double, and triple excitations, including CCSD(T) for all species, CCSD(2)T and CR-CC(2,3) for species with n = 1–3, and CCSDt, CC(t;3), and CCSDT for species with n = 1 and 2. We have used augmented polarized–valence and polarized–core–valence correlation-consistent basis sets. We have found that the geometry and binding energy of the weakly bound Mg 2 dimer requires a robust treatment of connected triple excitations, represented in this work by the CR-CC(2,3), CC(t;3), and full CCSDT methods, which are more accurate than the popular quasi-perturbative CCSD(T) approximation, but CCSD(T) is sufficiently accurate to be applied to other Mg clusters. We have also demonstrated that for all Mg clusters examined in this study, hybrid XC functionals generally have higher accuracy than local ones, with PW6B95, SOGGA11-X, M11, and PWB6K being the most accurate, both for the geometries and for the binding energies, ionization potentials, and electron-detachment energies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Spectroscopic study of the coupling effect between the two gaps of magnesium diboride on its RF properties

This program studied the two-gap nature of magnesium diboride and its possible effects on the superconducting rf properties of this material. Magnesium diboride (MgB 2 ) is a BCS superconductor with a superconducting critical temperature of 39 K, high critical current density and no weak link behavior across the grain boundary. These properties make this material ideal for both power applications and electronic devices. In particular, the high superconducting critical temperature and high thermodynamic field suggests that MgB 2 could be an ideal material also for superconducting radio frequency (SRF) cavities operating at a much higher temperature than Nb cavities and, therefore, reducing noticeably the cryogenics costs. However, MgB 2 is a two gap superconductor and it has been suggested that the RF properties are dominated by the smaller gap, which would make this material not competitive with Nb and especially Nb 3 Sn. The main problem does not seem to be the double-gap nature of this material but rather the weak-coupling of the two gaps that in the presence of an RF field suppresses superconductivity all together at fields much lower than the thermodynamic field. The main goal of this proposal is to address the fundamental question of the coupling between the two gaps in MgB 2 and understand if it is possible to control it and ultimately improve the RF performance of MgB 2 . The project studied these questions by measuring the density of states in the presence of an in-plane current and focused on the effect of controlled disorder. Disorder, indeed, provides an important knob to tune the properties of MgB2 and provides the possibility of changing the coupling between the two bands, making this material a competitive material for SRF applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water

Nuclear Magnetic Resonance (NMR) relaxation is sensitive to the local structure and dynamics around the probed nuclei. The Electric Field Gradient (EFG) is the key microscopic quantity to understand the NMR relaxation of quadrupolar ions, such as {sup 7}Li{sup +}, {sup 23}Na{sup +}, {sup 25}Mg{sup 2+}, {sup 35}Cl{sup −}, {sup 39}K{sup +}, or {sup 133}Cs{sup +}. Using molecular dynamics simulations, we investigate the statistical and dynamical properties of the EFG experienced by alkaline, alkaline Earth, and chloride ions at infinite dilution in water. Specifically, we analyze the effect of the ionic charge and size on the distribution of the EFG tensor and on the multi-step decay of its auto-correlation function. The main contribution to the NMR relaxation time arises from the slowest mode, with a characteristic time on the picosecond time scale. The first solvation shell of the ion plays a dominant role in the fluctuations of the EFG, all the more that the ion radius is small and its charge is large. We propose an analysis based on a simplified charge distribution around the ion, which demonstrates that the auto-correlation of the EFG, hence the NMR relaxation time, reflects primarily the collective translational motion of water molecules in the first solvation shell of the cations. Our findings provide a microscopic route to the quantitative interpretation of NMR relaxation measurements and open the way to the design of improved analytical theories for NMR relaxation for small ionic solutes, which should focus on water density fluctuations around the ion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Developing Quantum Levitation of ICF Capsules Coated with MgB 2 Thin Films

Current inertial confinement fusion (ICF) capsule support technologies create implosion perturbations which reduce fusion yield, driving the search for new support paradigms. Quantum levitation of the capsule will eliminate the requirement of a physical support structure, increasing fusion yield. The application of an external magnetic field to a capsule coated with a superconducting film can provide the necessary conditions for levitation. Magnesium diboride (MgB 2 ) is an attractive option for ICF applications as it has a high reported superconducting transition temperature of 39 K and is a low Z compound. This project is part of an ongoing effort which seeks to coat ICF capsules with a thin layer of superconducting MgB 2 . This project studied the synthesis of MgB 2 and diffusion/reaction kinetics of B/Mg/B m ultilayer thin films. These films were sputter deposited on flat glassy carbon substrates. Films were annealed in a tube furnace at temperatures between 400 °C and 650 °C for a total of 29 hours with film characterization done at predetermined intervals. At each interval, superconducting properties of the samples were evaluated with superconducting quantum interference device (SQUID) magnetometry, while Rutherford backscattering (RBS) with 2 MeV 4 He + ions was done to determine the composition and depth profile of the films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize surface morphology. Superconducting behavior was observed in thin films annealed at and above 450 °C. Formation of superconducting MgB 2 at 450 °C h as not been previously reported below 500 °C. The surface of the samples annealed at 500 °C and below was smooth with a measured roughness of ~3 nm. After 29 hours of annealing time, the 450 °C sample had a transition temperature of 27.3 K. The highest transition temperature measured was 30.9 K and was associated with a sample annealed for 29 hours at 650 °C. Transition temperatures were weakly positively correlated with annealing temperature and showed dependence on initial structural quality and oxygen contamination. Current research is attempting to synthesize superconducting MgB 2 coatings on spherical Si beads with the findings of this study. Future efforts are focused on the construction and testing of a levitation apparatus.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Characterisation of magnesium potassium phosphate cements blended with fly ash and ground granulated blast furnace slag

Magnesium potassium phosphate cements (MKPCs), blended with 50 wt.% fly ash (FA) or ground granulated blast furnace slag (GBFS) to reduce heat evolution, water demand and cost, were assessed using compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy on {sup 25}Mg, {sup 27}Al, {sup 29}Si, {sup 31}P and {sup 39}K nuclei. We present the first definitive evidence that dissolution of the glassy aluminosilicate phases of both FA and GBFS occurred under the pH conditions of MKPC. In addition to the main binder phase, struvite-K, an amorphous orthophosphate phase was detected in FA/MKPC and GBFS/MKPC systems. It was postulated that an aluminium phosphate phase was formed, however, no significant Al–O–P interactions were identified. High-field NMR analysis of the GBFS/MKPC system indicated the potential formation of a potassium-aluminosilicate phase. This study demonstrates the need for further research on these binders, as both FA and GBFS are generally regarded as inert fillers within MKPC.

36 MATERIALS SCIENCE↗
DOE OSTI2013

In-Beam γ -Ray Spectroscopy of Mg 34 , 36 , 38 : Merging the N = 20 and N = 28 Shell Quenching

Neutron-rich N = 22, 24, 26 magnesium isotopes were studied in this paper via in-beam γ-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory following secondary fragmentation reactions on a carbon target at ≈ 200 MeV /nucleon. In the one- and two-proton removal channels from 39 Al and 40 Si beams, two distinct γ-ray transitions were observed in 38 Mg, while in the one-proton removal reaction from 37 Al a new transition was observed in addition to the known 2 + 1 → 0 + g.s. decay. From the experimental systematics and comparison to theoretical predictions it is concluded that the transitions belong to the 2 + 1 → 0 + g.s. and 4 + 1 → 2 + 1 decays in 36 Mg and 38 Mg, respectively. For 34 Mg, previously reported 2 + 1 and 4 + 1 level energies were remeasured. Finally, the deduced E(4 + 1 )/E(2 + 1 ) ratios for 34,36,38 Mg of 3.14(5), 3.07(5), and 3.07(5) are almost identical and suggest the emergence of a large area of deformation extending from the N = 20 to the N = 28 shell quenching.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Fostering a Guiding Multiscale Model for the Development of Advanced MgB 2 Hydrogen Storage Materials (Final Technical Report)

Project Goal and Objective. The demand for energy and for an upgraded energy infrastructure has steadily grown, as have the needs for energy independence and alternatives to our reliance on petroleum. Hydrogen is considered the most viable fuels for wide-scale implementation in the near future as it is less-polluting, non-toxic, and has more stored energy than petroleum. It is envisioned that hydrogen can eventually become the prime energy carrier, integrating the transportation, grid, and chemical sectors in a way that improves resiliency, diversifies feedstocks, and affords new economic opportunities. A key remaining challenge is the development materials with enhanced gravimetric and volumetric hydrogen storage capacities that offer a higher performance than compressed gas. These materials would eliminate the need for large-scale compression, thereby dramatically reducing the footprint and cost of gas storage. The high gravimetric and volumetric hydrogen capacities of complex hydrides has prompted an intensive investigation of the potential of this class of materials as hydrogen storage media over the past 25 years. Among the many complex hydrides that have been explored, magnesium borohydride, Mg(BH 4 ) 2 , has been found to possess the best combination of practical thermodynamic properties. These include a gravimetric H 2 density of 14.9 wt% H 2 and thermodynamics for the dehydrogenation of Mg(BH 4 ) 2 to MgB 2 (equation 1) (ΔH° = 39 kJ/mol H 2 , ΔS = 112 J/K mol H 2 ) which lie in the narrow window required Mg(BH 4 ) 2 $\Leftrightarrow$ MgB 2 + 4 H 2 (1) for reversibility under moderate pressure and temperature. However, overcoming the extremely slow kinetics of the reversible release of hydrogen by this material in the solid state is a daunting challenge. At temperatures greater than 400 °C, the borohydride releases up to 14 wt% hydrogen giving MgB 2 . We discovered that the direct re-hydrogenation of MgB 2 to Mg(BH 4 ) 2 can be accomplished under 950 bar H 2 at 400 °C. While this demonstrated that complete reversibility can be achieved, the conditions employed are far too extreme for commercial hydrogen storage applications. More recently, we found through US DOE funded research projects (EERE HyMARC and HySCOR), that hydrogen cycling, can be accomplish at much milder conditions upon modification of the borohydride or boride. Guided by these discoveries these discoveries, the objective of this research project was to obtain key information that will enable the development of a model of reversible hydrogenation of MgB 2 to Mg(BH 4 ) 2 . The ultimate goal of our efforts is to attain a model of this transformation that can be utilized to accelerate development further advanced materials. This project directly follows on discoveries that were made over the course of a US DOE, EERE HyMARC project that was focused on improvement of the hydrogen cycling kinetics of modified MgB 2 . We found that that mechanical milling with graphene results the desired, pronounced kinetic enhancement. The dramatic lowering of the conditions required for the hydrogenation of MgB 2 is a significant step towards overcoming its chemical inertness allowing its development as a practical onboard hydrogen storage material. However, the exact nature of the modification(s) of MgB 2 that is responsible for its activation towards hydrogenation is completely unknown. This situation is not unique, as efforts to develop hydrogen storage materials typically have a narrow focus rather than a comprehensive approach that takes atomic level bonding and structure; molecular dynamics; long range, nano- and mesoscale-structure and their interconnection all into account. The goal of this project was the development of a comprehensive, multi-scale computational model of reversible hydrogenation of MgB 2 to Mg(BH 4 ) 2 that can be utilized for development of higher performance versions of the modified material. Development of the model requires determination of: 1) the bulk, nano-scale, and meso-scale structural changes occurring at elevated pressure following mechano-chemical modification of MgB 2 ; 2) the reaction pathway of the reversible hydrogenation of MgB 2 to Mg(BH 4 ) 2 ; 3) the effect of elevated pressure and mechano-chemical modification on the chemical reaction pathways; 4) the interactions at solid-gas interfaces; and particle surfaces; and 5) the kinetics and thermodynamic parameters associated with each step of the hydrogenation reaction pathway. This investigation required advanced techniques as preliminary, standard XRD, 11 B NMR, and FTIR analysis showed no signs of material modification. In order to gain this level of understanding of modified MgB 2 , required the teaming of a diverse group of experts and state-of-the art experimental capabilities at the University of Hawaii at Manoa (UHM) and collaborating National Laboratories: Craig Jensen , Department of Chemistry (PI and Project Director), solid state, solution, and high pressure NMR spectroscopy; solid-state synthesis; and high pressure hydrogenation (collaboration with SNL); Godwin Severa , Hawaii Natural Energy Institute (co-PI) calorimetry; infrared and Raman spectroscopy (collaboration with NREL); Dera , high pressure X-ray diffraction including in situ experiments (collaboration with ANL); Hope Ishii , Hawaii Institute of Geophysics electron microscopy investigations (collaboration with LBNL); and Joe Brown , Mechanical Engineering , material electronic structure and electric field effects.

08 HYDROGEN↗
DOE OSTI2022

Experimental X-ray Charge-Density Studies–A Suitable Probe for Superconductivity? A Case Study on MgB 2

Case studies of 1T-TiSe 2 and YBa 2 Cu 3 O 7-δ have demonstrated that X-ray diffraction (XRD) studies can be used to trace even subtle structural phase transitions which are inherently connected with the onset of superconductivity in these benchmark systems. However, the utility of XRD in the investigation of superconductors like MgB 2 lacking an additional symmetry-breaking structural phase transition is not immediately evident. Nevertheless, high-resolution powder XRD experiments on MgB 2 in combination with maximum entropy method analyses hinted at differences between the electron density distributions at room temperature and 15 K, that is, below the T c of approx. 39 K. The high-resolution single-crystal XRD experiments in combination with multipolar refinements presented here can reproduce these results but show that the observed temperature-dependent density changes are almost entirely due to a decrease of atomic displacement parameters as a natural consequence of a reduced thermal vibration amplitude with decreasing temperature. Our investigations also shed new light on the presence or absence of magnesium vacancies in MgB 2 samples–a defect type claimed to control the superconducting properties of the compound. Here, we propose that previous reports on the tendency of MgB 2 to form non-stoichiometric Mg 1–x B 2 phases (1 – x ~ 0.95) during high-temperature (HT) synthesis might result from the interpretation of XRD data of insufficient resolution and/or usage of inflexible refinement models. Indeed, advanced refinements based on an Extended Hansen–Coppens multipolar model and high-resolution X-ray data, which consider explicitly the contraction of core and valence shells of the magnesium cations, do not provide any significant evidence for the formation of non-stoichiometric Mg 1–x B 2 phases during HT synthesis.

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

Enhanced magnetism and ferroelectricity in epitaxial Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3}/CoFe{sub 2}O{sub 4}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3} multiferroic heterostructures grown using dual-laser ablation technique

PbZr{sub 0.52}Ti{sub 0.48}O{sub 3}/CoFe{sub 2}O{sub 4}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (PZT/CFO/LSMO) and PZT/LSMO heterostructures were grown on single-crystal MgO (100) substrates using the dual-laser ablation technique. X-ray diffraction confirmed the epitaxial relationship between the layers in the heterostructures. Magnetization measurements showed in-plane uniaxial magnetic anisotropy in PZT/CFO/LSMO with enhanced saturation magnetization of 288 emu/cm{sup 3} as compared to 244 emu/cm{sup 3} for PZT/LSMO. With the introduction of the hard magnetic CFO, the low coercivity of PZT/LSMO increased from 0.1 kOe to 1.4 kOe. Polarization measurements showed well-saturated square hysteresis loops for PZT/CFO/LSMO with enhanced remanent polarization (P{sub r}) values of 69 μC/cm{sup 2} at a coercive field (E{sub c}) of 88 kV/cm as compared to P{sub r} = 51 μC/cm{sup 2} at E{sub c} = 39 kV/cm for PZT/LSMO. The improved hard ferromagnetic and ferroelectric properties in PZT/CFO/LSMO as compared to PZT/LSMO make it desirable for multiferroic device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Electron/phonon coupling in group-IV transition-metal and rare-earth nitrides

Transport electron/phonon coupling parameters and Eliashberg spectral functions α{sub tr}{sup 2}F(ℏω) are determined for group-IV transition-metal (TM) nitrides TiN, ZrN, and HfN, and the rare-earth (RE) nitride CeN using an inversion procedure based upon temperature-dependent (4 < T < 300 K) resistivity measurements of high-crystalline-quality stoichiometric epitaxial films grown on MgO(001) by magnetically-unbalanced reactive magnetron sputtering. Transport electron/phonon coupling parameters λ{sub tr} vary from 1.11 for ZrN to 0.82 for HfN, 0.73 for TiN, and 0.44 for CeN. The small variation in λ{sub tr} among the TM nitrides and the weak coupling in CeN are consistent with measured superconducting transition temperatures 10.4 (ZrN), 9.18 (HfN), 5.35 (TiN), and <4 K for CeN. The Eliashberg spectral function describes the strength and energy spectrum of electron/phonon coupling in conventional superconductors. Spectral peaks in α{sup 2}F(ℏω), corresponding to regions in energy-space for which electrons couple to acoustic ℏω{sub ac} and optical ℏω{sub op} phonon modes, are centered at ℏω{sub ac} = 33 and ℏω{sub op} = 57 meV for TiN, 25 and 60 meV for ZrN, 18 and 64 meV for HfN, and 21 and 39 meV for CeN. The acoustic modes soften with increasing cation mass; optical mode energies remain approximately constant for the TM nitrides, but are significantly lower for the RE nitride due to a lower interatomic force constant. Optical/acoustic peak-intensity ratios are 1.15 ± 0.1 for all four nitrides, indicating similar electron/phonon coupling strengths α{sub tr}(ℏω) for both modes.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Heterostructures of Bi-4334 and MgB{sub 2} superconductors

We report the studies on hetero structures of Bi-4334 and MgB{sub 2} superconductors. The two superconductors were arranged in the form of bulk multilayers using hydraulic pressure system. X-ray diffraction pattern and dc magnetization studies confirm the presence of both superconducting phases in this try-layer hetero structured sample. The d.c magnetization shows the superconducting onset at 77 K and 39 K for Bi-4334 and MgB{sub 2} phases respectively. Critical current density (J{sub c}) is calculated from hysteresis loop of the sample in both in-plane field and out of plane field configurations. Inverted anisotropy in J{sub c} is observed due to enhancement of ab-plane properties because of multilayer growth process. Morphology of the samples at surface and interface of two superconducting layers is discussed in view of Field emission scanning electron microscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Studies on the Composite System of Bi-2212 Glass Ceramic and MgB{sub 2} Superconductors

The composites of glass ceramic Bi-2212 and MgB{sub 2} superconductors were prepared at ambient conditions. The transmission electron microscopy images of the composite samples illustrate the presence of glass ceramic inclusions in bulk MgB{sub 2}. Temperature-dependent magnetization of the composite samples shows two superconducting transitions: one at 80 K corresponding to the Bi-2212 phase and a second one at 39 K corresponding to the MgB{sub 2} phase, suggesting that the two superconducting phases are separated with clear boundaries. The critical current density (J{sub c}) and pinning force values are increased in composite systems by an order of magnitude compared to that of individual samples. The pinning mechanism in the composite sample is the same as in the matrix phase. Reduced field maxima (h{sub max}) are observed at 0.15 for composite samples. A low value of h{sub max} for composite samples indicates the random orientation of grain boundaries and repulsive pinning force in the composite samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Influence of hydrogen patterning gas on electric and magnetic properties of perpendicular magnetic tunnel junctions

To identify the degradation mechanism in magnetic tunnel junctions (MTJs) using hydrogen, the properties of the MTJs were measured by applying an additional hydrogen etch process and a hydrogen plasma process to the patterned MTJs. In these studies, an additional 50 s hydrogen etch process caused the magnetoresistance (MR) to decrease from 103% to 14.7% and the resistance (R) to increase from 6.5 kΩ to 39 kΩ. Moreover, an additional 500 s hydrogen plasma process decreased the MR from 103% to 74% and increased R from 6.5 kΩ to 13.9 kΩ. These results show that MTJs can be damaged by the hydrogen plasma process as well as by the hydrogen etch process, as the atomic bonds in MgO may break and react with the exposed hydrogen gas. Compounds such as MgO hydrate very easily. We also calculated the damaged layer width (DLW) of the patterned MTJs after the hydrogen etching and plasma processes, to evaluate the downscaling limitations of spin-transfer-torque magnetic random-access memory (STT-MRAM) devices. With these calculations, the maximum DLWs at each side of the MTJ, generated by the etching and plasma processes, were 23.8 nm and 12.8 nm, respectively. This result validates that the hydrogen-based MTJ patterning processes cannot be used exclusively in STT-MRAMs beyond 20 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Optical studies on Eu{sup 3+} doped boro-tellurite glasses

Eu{sup 3+} doped boro-tellurite glasses with the chemical composition (39-x)B{sub 2}O{sub 3}+30TeO{sub 2}+15MgO+15K{sub 2}O +xEu{sub 2}O{sub 3} (where x = 0.01, 0.1, 1, 2 and 3 wt%) have been prepared by following conventional melt quenching technique. Spectroscopic properties of the Eu{sup 3+} doped boro-tellurite glasses have been studied by recording the optical absorption and luminescence measurements. Through the optical absorption spectra, bonding parameters ({beta}-bar, {delta}) have been calculated to identify the ionic/covalent nature of the glasses. Judd-Ofelt (JO) analysis have been carried out using the luminescence spectra. The JO parameters ({Omega}{sub {lambda}}= 2, 4 and 6) were used to calculate the radiative properties for the {sup 5}D{sub 0}{yields}{sup 7}F{sub J} (J = 1, 2, 3 and 4) emission transitions of the Eu{sup 3+} ions. The change in optical properties with the variation of Eu{sup 3+} ion concentration have been studied and discussed with similar studies.

36 MATERIALS SCIENCE↗
DOE OSTI2016

MAGiiCAT IV. Kinematics of the circumgalactic medium and evidence for quiescent evolution around red galaxies

The equivalent widths of Mg II absorption in the circumgalactic medium (CGM) trace the global star formation rate up to z < 6, are larger for star-forming galaxies than passively evolving galaxies, and decrease with increasing distance from the galaxy. We delve further into the physics involved by investigating gas kinematics and cloud column density distributions as a function of galaxy color, redshift, and projected distance from the galaxy (normalized by galaxy virial radius, D/R{sub vir}). For 39 isolated galaxies at 0.3 < z{sub gal} < 1.0, we have detected Mg II absorption in high-resolution (Δv ≃ 6.6 km s{sup −1}) spectra of background quasars within a projected distance of 7 < D < 190 kpc. We characterize the absorption velocity spread using pixel-velocity two-point correlation functions. Velocity dispersions and cloud column densities for blue galaxies do not differ with redshift nor with D/R{sub vir}. This suggests that outflows continually replenish the CGM of blue galaxies with high velocity dispersion, large column density gas out to large distances. Conversely, absorption hosted by red galaxies evolves with redshift where the velocity dispersions (column densities) are smaller (larger) at z{sub gal} < 0.656. After taking into account larger possible velocities in more massive galaxies, we find that there is no difference in the velocity dispersions or column densities for absorption hosted by red galaxies with D/R{sub vir}. Thus, a lack of outflows in red galaxies causes the CGM to become more quiescent over time, with lower velocity dispersions and larger column densities toward lower z{sub gal}. The quenching of star formation appears to affect the CGM out to D/R{sub vir} = 0.75.

79 ASTRONOMY AND ASTROPHYSICS↗