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Sample records for spin-polarized calculations give

  1. Electric field induced spin polarization oscillation in nonmagnetic benzene/Cu(100) interface: First principles calculations

    Science.gov (United States)

    Yuan, X. B.; Cai, L. L.; Tian, Y. L.; Hu, G. C.; Ren, J. F.

    2018-01-01

    First-principles calculation are presented to study the influences of external electric fields on the spin polarization properties of benzene/Cu(100) system which do not contain any magnetic atom. Our simulations show that an obvious spontaneous spin polarization oscillation occurred in the benzene molecule when the electric fields are applied. The density of states (DOS), spin density distributions, charge transfer properties are also obtained. It is found that the p-d orbital coupling between the benzene molecule and the electrode leads to spin non-degeneration of the DOS near the fermi energy, so the transferred charges from the Cu atoms to the molecule will fill these spin non-degenerate coupled orbitals, and then the benzene molecule becomes spin polarized. The strength of the p-d orbital coupling as well as the transferred charges oscillated with the external electric fields, which induce spin polarization oscillation. The results are favorable for the understanding of spin polarization properties in organic/nonmagnetic metal structures.

  2. Pellet fusion gain calculations modified by electrostatic double layers and by spin polarized nuclei

    International Nuclear Information System (INIS)

    Hora, H.; Cicchitelli, L.; Elijah, J.S.; Ghatak, A.K.; Goldsworthy, M.T.; Lalousis, P.; Eliezer, S.

    1984-01-01

    All preceding hydrodynamic computations of plasmas are wrong if the thermal conductivity is essential because electronic thermal conductivity is decreased in plasma inhomogeneities due to electrostatic double layers. In the worst case, ionic conductivity remains. We compare this with a possible electronic conductivity by the fast tail of the energy distribution. Using the volume ignition for fusion gain computations, we study the increase of gain by spin-polarization of nuclei for the DT reaction especially in non-linear ranges. Gain can increase by a factor 3.1. Contents are the following: electrostatic fields and double layers in inhomogeneous plasma, change of thermal conduction by double layers, consequences for pellet fusion, gain calculation with spin polarized nuclei. (Mori, K.)

  3. Magnetoresistance through spin-polarized p states

    International Nuclear Information System (INIS)

    Papanikolaou, Nikos

    2003-01-01

    We present a theoretical study of the ballistic magnetoresistance in Ni contacts using first-principles, atomistic, electronic structure calculations. In particular we investigate the role of defects in the contact region with the aim of explaining the recently observed spectacular magnetoresistance ratio. Our results predict that the possible presence of spin-polarized oxygen in the contact region could explain conductance changes by an order of magnitude. Electronic transport essentially occurs through spin-polarized oxygen p states, and this mechanism gives a much higher magnetoresistance than that obtained assuming clean atomically sharp domain walls alone

  4. Tailoring electronic structure of α-AlH3 to enhance spin polarization: Insights from density functional calculations

    Science.gov (United States)

    Lu, Yi-Lin; Dong, Shengjie; Zhou, Baozeng; Sun, Lili; Zhao, Hui; Wu, Ping

    2017-09-01

    The effects of 3d transition metals doping on the structural, electronic, and magnetic properties of aluminum hydride were investigated based on spin-polarized first-principles calculations. The studies indicated that V, Cr, Mn, and Fe doping could produce polarization of high-spin state, while Co and Ni doping would induce polarization of low-spin state. It was found that the magnetic ground state depended on the distance between two substitutions and the long-range ferromagnetic coupling was achieved upon doping V, Mn, and Fe. The present work indicated that the introduced 3d-block dopants could tailor aluminum hydride into either a potential half-metallic or n-type magnetic semiconductor by tuning the valence electrons of the impurities. The main findings of this work pointed out the possibilities of the applications of hydrides in future hydride electronics and spintronics.

  5. Calculations of static properties of spin-polarized 3He--4He mixtures

    International Nuclear Information System (INIS)

    Owers-Bradley, J.R.; Bowley, R.M.; Main, P.C.

    1985-01-01

    The theory of dilute mixtures of 3 He in 4 He that have been polarized by a strong magnetic field is developed. The interaction between the quasiparticles is taken to be constant, an approximation valid at low temperatures. The polarization of the mixture depends on the strength of the interaction. The internal energy, the specific heat, the osmotic pressure, and the velocity of second sound are also calculated. The specific heat is relatively insensitive to the interaction, but it does change significantly with magnetic field. The osmotic pressure is more sensitive to the effects of the interaction for some 3 He concentrations and temperatures. The velocity of second sound behaves qualitatively like the osmotic pressure. The measurement of these quantities as a function of temperature and magnetic field is discussed with a view to obtaining the strength of the interaction between quasiparticles

  6. Spin polarized electron tunneling and magnetoresistance in molecular junctions.

    Science.gov (United States)

    Szulczewski, Greg

    2012-01-01

    This chapter reviews tunneling of spin-polarized electrons through molecules positioned between ferromagnetic electrodes, which gives rise to tunneling magnetoresistance. Such measurements yield important insight into the factors governing spin-polarized electron injection into organic semiconductors, thereby offering the possibility to manipulate the quantum-mechanical spin degrees of freedom for charge carriers in optical/electrical devices. In the first section of the chapter a brief description of the Jullière model of spin-dependent electron tunneling is reviewed. Next, a brief description of device fabrication and characterization is presented. The bulk of the review highlights experimental studies on spin-polarized electron tunneling and magnetoresistance in molecular junctions. In addition, some experiments describing spin-polarized scanning tunneling microscopy/spectroscopy on single molecules are mentioned. Finally, some general conclusions and prospectus on the impact of spin-polarized tunneling in molecular junctions are offered.

  7. Dynamic nuclear spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Stuhrmann, H.B. [GKSS-Forschungszentrum Geesthacht GmbH (Germany)

    1996-11-01

    Polarized neutron scattering from dynamic polarized targets has been applied to various hydrogenous materials at different laboratories. In situ structures of macromolecular components have been determined by nuclear spin contrast variation with an unprecedented precision. The experiments of selective nuclear spin depolarisation not only opened a new dimension to structural studies but also revealed phenomena related to propagation of nuclear spin polarization and the interplay of nuclear polarisation with the electronic spin system. The observation of electron spin label dependent nuclear spin polarisation domains by NMR and polarized neutron scattering opens a way to generalize the method of nuclear spin contrast variation and most importantly it avoids precontrasting by specific deuteration. It also likely might tell us more about the mechanism of dynamic nuclear spin polarisation. (author) 4 figs., refs.

  8. Spin-polarized deuterium in magnetic traps

    International Nuclear Information System (INIS)

    Koelman, J.M.V.A.; Stoof, H.T.C.; Verhaar, B.J.; Walraven, J.T.M.

    1987-01-01

    We have calculated the spin-exchange two-body rate constants associated with the population dynamics of the hyperfine levels of atomic deuterium as a function of magnetic field in the Boltzmann zero-temperature limit. Results indicate that a gas of low-field--seeking deuterium atoms trapped in a static magnetic field minimum decays rapidly into an ultrastable gas of doubly spin-polarized deuterium. We also discuss the temperature dependence of various effects

  9. Spin-polarized photoemission from SiGe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ferrari, A.; Bottegoni, F.; Isella, G.; Cecchi, S.; Chrastina, D.; Finazzi, M.; Ciccacci, F. [LNESS-Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy)

    2013-12-04

    We apply the principles of Optical Orientation to measure by Mott polarimetry the spin polarization of electrons photoemitted from different group-IV heterostructures. The maximum measured spin polarization, obtained from a Ge/Si{sub 0.31}Ge{sub 0.69} strained film, undoubtedly exceeds the maximum value of 50% attainable in bulk structures. The explanation we give for this result lies in the enhanced band orbital mixing between light hole and split-off valence bands as a consequence of the compressive strain experienced by the thin Ge layer.

  10. An enhancement of spin polarization by multiphoton pumping in semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M. Idrish, E-mail: m.miah@griffith.edu.au [Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)

    2011-08-15

    Highlights: {yields} Multiphoton pumping and spin generation in semiconductors. {yields} Optical selection rules for inter-band transitions. {yields} Calculations of spin polarization using band-energy model and the second order perturbation theory. {yields} Enhancement of the electronic spin polarization. - Abstract: A pump-probe spectroscopic study has been carried out in zinc-blende bulk semiconductors. In the semiconductor samples, a spin-polarized carrier population is produced by the absorption of a monochromatic circularly polarized light beam with two-photon energy above the direct band gap in bulk semiconductors. The production of a carrier population with a net spin is a consequence of the optical selection rules for the heavy-hole and light-hole valence-to-conduction band transitions. This production is probed by the spin-dependent transmission of the samples in the time domain. The spin polarization of the conduction-band-electrons in dependences of delay of the probe beam as well as of pumping photon energy is estimated. The spin polarization is found to depolarize rapidly for pumping energy larger than the energy gap of the split-off band to the conduction band. From the polarization decays, the spin relaxation times are also estimated. Compared to one-photon pumping, the results, however, show that an enhancement of the spin-polarization is achieved by multiphoton excitation of the samples. The experimental results are compared with those obtained in calculations using second order perturbation theory of the spin transport model. A good agreement between experiment and theory is obtained. The observed results are discussed in details.

  11. An enhancement of spin polarization by multiphoton pumping in semiconductors

    International Nuclear Information System (INIS)

    Miah, M. Idrish

    2011-01-01

    Highlights: → Multiphoton pumping and spin generation in semiconductors. → Optical selection rules for inter-band transitions. → Calculations of spin polarization using band-energy model and the second order perturbation theory. → Enhancement of the electronic spin polarization. - Abstract: A pump-probe spectroscopic study has been carried out in zinc-blende bulk semiconductors. In the semiconductor samples, a spin-polarized carrier population is produced by the absorption of a monochromatic circularly polarized light beam with two-photon energy above the direct band gap in bulk semiconductors. The production of a carrier population with a net spin is a consequence of the optical selection rules for the heavy-hole and light-hole valence-to-conduction band transitions. This production is probed by the spin-dependent transmission of the samples in the time domain. The spin polarization of the conduction-band-electrons in dependences of delay of the probe beam as well as of pumping photon energy is estimated. The spin polarization is found to depolarize rapidly for pumping energy larger than the energy gap of the split-off band to the conduction band. From the polarization decays, the spin relaxation times are also estimated. Compared to one-photon pumping, the results, however, show that an enhancement of the spin-polarization is achieved by multiphoton excitation of the samples. The experimental results are compared with those obtained in calculations using second order perturbation theory of the spin transport model. A good agreement between experiment and theory is obtained. The observed results are discussed in details.

  12. Nuclear spin polarization of targets

    International Nuclear Information System (INIS)

    Happer, W.

    1990-01-01

    Lasers can be used to produce milligrams to grams of noble gas nuclei with spin polarizations in excess of 50%. These quantities are sufficient to be very useful targets in nuclear physics experiments. Alkali-metal atoms are used to capture the angular momentum of circularly polarized laser photons, and the alkali-metal atoms transfer their angular momentum to noble gas atoms in binary or three-body collisions. Non-radiative collisions between the excited alkali atoms and molecular quenching gases are essential to avoid radiation trapping. The spin exchange can involve gas-phase van der Waals molecules, consisting of a noble gas atom and an alkali metal atom. Surface chemistry is also of great importance in determining the wall-induced relaxation rates of the noble gases

  13. Thermal stability of tunneling spin polarization

    International Nuclear Information System (INIS)

    Kant, C.H.; Kohlhepp, J.T.; Paluskar, P.V.; Swagten, H.J.M.; Jonge, W.J.M. de

    2005-01-01

    We present a study of the thermal stability of tunneling spin polarization in Al/AlOx/ferromagnet junctions based on the spin-polarized tunneling technique, in which the Zeeman-split superconducting density of states in the Al electrode is used as a detector for the spin polarization. Thermal robustness of the polarization, which is of key importance for the performance of magnetic tunnel junction devices, is demonstrated for post-deposition anneal temperatures up to 500 o C with Co and Co 90 Fe 10 top electrodes, independent of the presence of an FeMn layer on top of the ferromagnet

  14. Effect of spin polarization on the structural properties and bond ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 39; Issue 6. Effect of spin ... Volume 39 Issue 6 October 2016 pp 1427-1434 ... Spin-polarization calculations show that ferromagnetic state (FM) is stable for FexB structures and carry magnetic moment of 1.12, 1.83 and 2.03 μ B inFeB, Fe 2 B and Fe 3 B, respectively.

  15. Spin-polarized ballistic conduction through correlated Au-NiMnSb-Au heterostructures

    KAUST Repository

    Morari, C.

    2017-11-20

    We examine the ballistic conduction through Au-NiMnSb-Au heterostructures consisting of up to four units of the half-metallic NiMnSb in the scattering region, using density functional theory (DFT) methods. For a single NiMnSb unit the transmission function displays a spin polarization of around 50% in a window of 1eV centered around the Fermi level. By increasing the number of layers, an almost complete spin polarization of the transmission is obtained in this energy range. Supplementing the DFT calculations with local electronic interactions, of Hubbard-type on the Mn sites, leads to a hybridization between the interface and many-body states. The significant reduction of the spin polarization seen in the density of states is not apparent in the spin polarization of the conduction electron transmission, which suggests that the hybridized interface and many-body induced states are localized.

  16. Optical pumping production of spin polarized hydrogen

    International Nuclear Information System (INIS)

    Knize, R.J.; Happer, W.; Cecchi, J.L.

    1984-01-01

    There has been much interest recently in the production of large quantities of spin polarized hydrogen in various fields including controlled fusion, quantum fluids, high energy, and nuclear physics. One promising method for the development of large quantities of spin polarized hydrogen is the utilization of optical pumping with a laser. Optical pumping is a process where photon angular momentum is converted into electron and nuclear spin. The advent of tunable CW dye lasers (approx. 1 watt) allow the production of greater than 10 18 polarized atoms/sec. We have begun a program at Princeton to investigate the physics and technology of using optical pumping to produce large quantities of spin polarized hydrogen. Initial experiments have been done in small closed glass cells. Eventually, a flowing system, open target, or polarized ion source could be constructed

  17. Biaxial-stress-driven full spin polarization in ferromagnetic hexagonal chromium telluride

    Energy Technology Data Exchange (ETDEWEB)

    Xiao, Xiang-Bo; Li, Jun [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Liu, Bang-Gui, E-mail: bgliu@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190 (China)

    2017-03-15

    It is important to spintronics to achieve fully-spin-polarized magnetic materials that are stable and can be easily fabricated. Here, through systematical density-functional-theory investigations, we achieve high and even full spin polarization for carriers in the ground-state phase of CrTe by applying tensile biaxial stress. The resulting strain is tensile in the xy plane and compressive in the z axis. With the in-plane tensile strain increasing, the ferromagnetic order is stable against antiferromagnetic fluctuations, and a half-metallic ferromagnetism is achieved at an in-plane strain of 4.8%. With the spin-orbit coupling taken into account, the spin polarization is equivalent to 97% at the electronic transition point, and then becomes 100.0% at the in-plane strain of 6.0%. These make us believe that the full-spin-polarized ferromagnetism in this stable and easily-realizable hexagonal phase could be realized soon, and applied in spintronics. - Highlights: • Full spin polarization in the hexagonal ground-state phase of CrTe by biaxial stress. • The stress produces in-plane tensile strain and perpendicular compressive strain. • Reliable electronic structure is calculated with improved exchange functional. • Spin polarization is calculated with spin-orbit coupling taken into account.

  18. Calculations of spin-polarized Goos-Hänchen displacement in magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit couplings

    Science.gov (United States)

    Lu, Mao-Wang; Chen, Sai-Yan; Zhang, Gui-Lian; Huang, Xin-Hong

    2018-04-01

    We theoretically investigate Goos-Hänchen (GH) displacement by modelling the spin transport in an archetypal device structure—a magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit coupling (SOC). Both Rashba and Dresselhaus SOCs are taken into account. The degree of spin-polarized GH displacement can be tuned by Rashba or Dresselhaus SOC, i.e. interfacial confining electric field or strain engineering. Based on such a semiconductor nanostructure, a controllable spatial spin splitter can be proposed for spintronics applications.

  19. Spin-Polarized Tunneling through Chemical Vapor Deposited Multilayer Molybdenum Disulfide.

    Science.gov (United States)

    Dankert, André; Pashaei, Parham; Kamalakar, M Venkata; Gaur, Anand P S; Sahoo, Satyaprakash; Rungger, Ivan; Narayan, Awadhesh; Dolui, Kapildeb; Hoque, Md Anamul; Patel, Ram Shanker; de Jong, Michel P; Katiyar, Ram S; Sanvito, Stefano; Dash, Saroj P

    2017-06-27

    The two-dimensional (2D) semiconductor molybdenum disulfide (MoS 2 ) has attracted widespread attention for its extraordinary electrical-, optical-, spin-, and valley-related properties. Here, we report on spin-polarized tunneling through chemical vapor deposited multilayer MoS 2 (∼7 nm) at room temperature in a vertically fabricated spin-valve device. A tunnel magnetoresistance (TMR) of 0.5-2% has been observed, corresponding to spin polarization of 5-10% in the measured temperature range of 300-75 K. First-principles calculations for ideal junctions result in a TMR up to 8% and a spin polarization of 26%. The detailed measurements at different temperature, bias voltages, and density functional theory calculations provide information about spin transport mechanisms in vertical multilayer MoS 2 spin-valve devices. These findings form a platform for exploring spin functionalities in 2D semiconductors and understanding the basic phenomena that control their performance.

  20. Spin polarization tuning in the graphene quantum dot by using in-plane external electric field

    International Nuclear Information System (INIS)

    Modarresi, M.; Roknabadi, M.R.; Shahtahmasebi, N.

    2014-01-01

    Electronic, magnetic and transport properties of a nano-graphene dot have been studied by using the DFT and tight binding methods. In the tight binding calculations, the interaction between electrons is modeled using the Hubbard Hamiltonian. By comparison between the eigen-values and density of states in the tight binding and DFT models, we tabulate a set of tight-binding parameters to describe graphene quantum dots for future works. The effects of a single vacancy and an in-plane external electric field on the spin-dependent transport of graphene quantum dot have been investigated. Transport through GQD between two GNR is studied by using Green's function formalism. Our results confirm an intrinsic spin-dependent current and relatively large spin polarization through the GQD in the presence of a single vacancy and zigzag edge. It is also shown that an in-plane external electric field controls the spin-polarization in graphene quantum dot. - Graphical abstract: We study the spin polarization in the presence of an external electric field. Highlights: • A tight binding study of transport through GNR/GQD/GNR is presented. • Our results show a relatively large spin polarization in the current–voltage curve. • Spin polarization is controlled by using an in-plane external electric field

  1. Peculiarities of spin polarization inversion at a thiophene/cobalt interface

    KAUST Repository

    Wang, Xuhui

    2013-03-20

    We perform ab initio calculations to investigate the spin polarization at the interface between a thiophene molecule and cobalt substrate. We find that the reduced symmetry in the presence of a sulfur atom (in the thiophene molecule) leads to a strong spatial dependence of the spin polarization of the molecule. The two carbon atoms far from the sulfur acquire a polarization opposite to that of the substrate, while the carbon atoms bonded directly to sulfur possess the same polarization as the substrate. We determine the origin of this peculiar spin interface property as well as its impact on the spin transport.

  2. Photo-Induced Electron Spin Polarization in a Narrow Band Gap Semiconductor Nanostructure

    International Nuclear Information System (INIS)

    Peter, A. John; Lee, Chang Woo

    2012-01-01

    Photo-induced spin dependent electron transmission through a narrow gap InSb/InGa x Sb 1−x semiconductor symmetric well is theoretically studied using transfer matrix formulism. The transparency of electron transmission is calculated as a function of electron energy for different concentrations of gallium. Enhanced spin-polarized photon assisted resonant tunnelling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level and compressed spin-polarization are observed. Our results show that Dresselhaus spin-orbit coupling is dominant for the photon effect and the computed polarization efficiency increases with the photon effect and the gallium concentration

  3. Construction of the spin-polarized slow positron beam with the RI source

    Energy Technology Data Exchange (ETDEWEB)

    Nakajyo, Terunobu; Tashiro, Mutsumi; Kanazawa, Ikuzo [Tokyo Gakugei Univ., Koganei (Japan); Komori, Fumio; Murata, Yoshimasa; Ito, Yasuo

    1997-03-01

    The electrostatic slow-positron beam is constructed by using {sup 22}Na source. We design the electrostatic lens, the system of the detector, and the Wien filter for the experiment`s system of the spin-polarized slow positron beam. The reemitted spin-polarized slow-positron spectroscopy is proposed for studying magnetic thin films and magnetic multilayers. We calculated the depolarized positron fractions in the Fe thin film Fe(10nm)/Cu(substrate) and the multilayers Cu(1nm)/Fe(10nm)/Cu(substrate). (author)

  4. Microscopic theory of fully spin-polarized /sup 3/He

    Energy Technology Data Exchange (ETDEWEB)

    Glyde, H.R.; Hernadi, S.I.

    1983-01-01

    The ground state energy (E), Landau parameters (F) and single particle energy spectrum (epsilon(kappa) and m/sup */) in fully spin polarized liquid /sup 3/He (/sup 3/He) are calculated directly from the bare interatomic potential within the Galitskii-Feynmann T-matrix and Hartree-Fock (GFHF) approximations. The E agrees well with variational calculations, the F with model calculations and the epsilon(kappa) and m/sup */ with results expected from nuclear matter. This suggests the effective interaction in /sup 3/He is dominated by hard core repulsion and Fermi statistics and that these components of the full interaction can be well described from first principles by a GF T-matrix. 36 references, 3 figures, 1 table.

  5. Spin-polarized spin excitation spectroscopy

    International Nuclear Information System (INIS)

    Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J

    2010-01-01

    We report on the spin dependence of elastic and inelastic electron tunneling through transition metal atoms. Mn, Fe and Cu atoms were deposited onto a monolayer of Cu 2 N on Cu(100) and individually addressed with the probe tip of a scanning tunneling microscope. Electrons tunneling between the tip and the substrate exchange energy and spin angular momentum with the surface-bound magnetic atoms. The conservation of energy during the tunneling process results in a distinct onset threshold voltage above which the tunneling electrons create spin excitations in the Mn and Fe atoms. Here we show that the additional conservation of spin angular momentum leads to different cross-sections for spin excitations depending on the relative alignment of the surface spin and the spin of the tunneling electron. For this purpose, we developed a technique for measuring the same local spin with a spin-polarized and a non-spin-polarized tip by exchanging the last apex atom of the probe tip between different transition metal atoms. We derive a quantitative model describing the observed excitation cross-sections on the basis of an exchange scattering process.

  6. Large positive spin polarization and giant inverse tunneling magnetoresistance in Fe/PbTiO3/Fe multiferroic tunnel junction

    International Nuclear Information System (INIS)

    Dai, Jian-Qing; Zhang, Hu; Song, Yu-Min

    2014-01-01

    We perform first-principles electronic structure and spin-dependent transport calculations of a multiferroic tunnel junction (MFTJ) with an epitaxial Fe/PbTiO 3 /Fe heterostructure. We predict a large positive spin-polarization (SP) and an intriguing giant inverse tunneling magnetoresistance (TMR) ratio in this tunnel junction. We demonstrate that the tunneling properties are determined by ferroelectric (FE) polarization screening and electronic reconstruction at the interface with lower electrostatic potential. The intricate complex band structure of PbTiO 3 , in particular the lowest decay rates concerning Pb 6p z and Ti 3d z2 states near the Γ ¯ point, gives rise to the large positive SP of the tunneling current in the parallel magnetic configuration. However, the giant inverse TMR ratio is attributed to the minority-spin electrons of the interfacial Ti 3d xz +3d yz orbitals which have considerably weight in the extended area around the Γ ¯ point at the Fermi energy and causes remarkable contributions to the conductance in the antiparallel magnetic configuration. - Highlights: • We study spin-dependent tunneling in Fe/PbTiO 3 /Fe multiferroic tunnel junction. • We find a large positive spin polarization in the parallel magnetic configuration. • An intriguing giant inverse TMR ratio (about −2000%) is predicted. • Complex band structure of PbTiO 3 causes the large positive spin polarization. • Negative TMR is due to minority-spin electrons of interfacial Ti d xz +d yz orbitals

  7. Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

    Science.gov (United States)

    Luengo-Kovac, M.; Huang, S.; Del Gaudio, D.; Occena, J.; Goldman, R. S.; Raimondi, R.; Sih, V.

    2017-11-01

    The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InxGa1 -xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.

  8. Transient charging and discharging of spin-polarized electrons in a quantum dot

    DEFF Research Database (Denmark)

    De Souza, Fabricio; Leao, S.A.; Gester, R. M.

    2007-01-01

    We study spin-polarized transient transport in a quantum dot coupled to two ferromagnetic leads subjected to a rectangular bias voltage pulse. Time-dependent spin-resolved currents, occupations, spin accumulation, and tunneling magnetoresistance TMR are calculated using both nonequilibrium Green...

  9. Spin polarization of electrons in a magnetic impurity doped ...

    Indian Academy of Sciences (India)

    Abstract. A theoretical model is presented in this paper for degree of spin polarization in a light emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different ...

  10. Spin-Polarization in Quasi-Magnetic Tunnel Junctions

    Science.gov (United States)

    Xie, Zheng-Wei; Li, Ling

    2017-05-01

    Spin polarization in ferromagnetic metal/insulator/spin-filter barrier/nonmagnetic metal, referred to as quasi-magnetic tunnel junctions, is studied within the free-electron model. Our results show that large positive or negative spin-polarization can be obtained at high bias in quasi-magnetic tunnel junctions, and within large bias variation regions, the degree of spin-polarization can be linearly tuned by bias. These linear variation regions of spin-polarization with bias are influenced by the barrier thicknesses, barrier heights and molecular fields in the spin-filter (SF) layer. Among them, the variations of thickness and heights of the insulating and SF barrier layers have influence on the value of spin-polarization and the linear variation regions of spin-polarization with bias. However, the variations of molecular field in the SF layer only have influence on the values of the spin-polarization and the influences on the linear variation regions of spin-polarization with bias are slight. Supported by the Key Natural Science Fund of Sichuan Province Education Department under Grant Nos 13ZA0149 and 16ZA0047, and the Construction Plan for Scientific Research Innovation Team of Universities in Sichuan Province under Grant No 12TD008.

  11. Spin polarization at the interface and tunnel magnetoresistance

    International Nuclear Information System (INIS)

    Itoh, H.; Inoue, J.

    2001-01-01

    We propose that interfacial states of imperfectly oxidized Al ions may exist in ferromagnetic tunnel junctions with Al-O barrier and govern both the spin polarization and tunnel conductance. It is shown that the spin polarization is positive independent of materials and correlates well with the tunnel magnetoresistance

  12. Effect of spin polarization on the structural properties and bond ...

    Indian Academy of Sciences (India)

    coupled to semi-empirical hardness theory proved effective in hardness prediction for the metal borides which agree well with the experimental values. These results would help to gain insight into the spin-polarized effect on the structural and bond hardness. Keywords. Iron boride; DFT; spin polarized; critical pressure; ...

  13. Spin polarization of electrons in a magnetic impurity doped ...

    Indian Academy of Sciences (India)

    A theoretical model is presented in this paper for degree of spin polarization in alight emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and ...

  14. Detecting Spin-Polarized Currents in Ballistic Nanostructures

    DEFF Research Database (Denmark)

    Potok, R.; Folk, J.; M. Marcus, C.

    2002-01-01

    We demonstrate a mesoscopic spin polarizer/analyzer system that allows the spin polarization of current from a quantum point contact in an in-plane magnetic field to be measured. A transverse focusing geometry is used to couple current from an emitter point contact into a collector point contact....

  15. Diffusion equation and spin drag in spin-polarized transport

    DEFF Research Database (Denmark)

    Flensberg, Karsten; Jensen, Thomas Stibius; Mortensen, Asger

    2001-01-01

    We study the role of electron-electron interactions for spin-polarized transport using the Boltzmann equation, and derive a set of coupled transport equations. For spin-polarized transport the electron-electron interactions are important, because they tend to equilibrate the momentum of the two-s...

  16. Spin-polarized transport in a δ-doped magnetic-barrier nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shuai; Lu, Mao-Wang, E-mail: maowanglu@126.com; Jiang, Ya-Qing; Chen, Sai-Yan

    2014-09-05

    We theoretically investigate the electron spin transport properties through a δ-doped magnetic-barrier nanostructure, which can be realized experimentally by depositing two identical ferromagnetic stripes with the opposite in-plane magnetization on the top of a semiconductor heterostructure in parallel configuration and by using atomic layer doping technique. The δ-doping dependent transmission, conductance and spin polarization are calculated exactly by analytically solving Schrödinger equation of the spin electron. It is found that the electronic spin-polarized behavior in this device can be manipulated by changing the weight and/or the position of the δ-doping. Therefore, such a device can be used as a controllable spin filter, which may be helpful for spintronics applications. - Highlights: • Spin-polarized transport in a δ-doped magnetic-barrier nanostructure is explored. • Both magnitude and sign of spin polarization depend on the δ-doping. • A controllable spin filter can be achieved for spintronics applications.

  17. Designing magnetic droplet soliton nucleation employing spin polarizer

    Science.gov (United States)

    Mohseni, Morteza; Mohseni, Majid

    2018-04-01

    We show by means of micromagnetic simulations that spin polarizer in nano-contact (NC) spin torque oscillators as the representative of the fixed layer in an orthogonal pseudo-spin valve can be employed to design and to control magnetic droplet soliton nucleation and dynamics. We found that using a tilted spin polarizer layer decreases the droplet nucleation time which is more suitable for high speed applications. However, a tilted spin polarizer increases the nucleation current and decreases the frequency stability of the droplet. Additionally, by driving the magnetization inhomogenously at the NC region, it is found that a tilted spin polarizer reduces the precession angle of the droplet and through an interplay with the Oersted field of the DC current, it breaks the spatial symmetry of the droplet profile. Our findings explore fundamental insight into nano-scale magnetic droplet soliton dynamics with potential tunability parameters for future microwave electronics.

  18. A frozen spin polarized target for S134

    CERN Multimedia

    1974-01-01

    The CERN-ETH, Zurich-Helsinki-Imperial College-Southampton Collaboration used a frozen spin polarized target together with the ETH spectrometer magnet to study spin effects (S134). Beam was d31 in South Hall

  19. Neutron stars with spin polarized self-interacting dark matter

    OpenAIRE

    Rezaei, Zeinab

    2018-01-01

    Dark matter, one of the important portion of the universe, could affect the visible matter in neutron stars. An important physical feature of dark matter is due to the spin of dark matter particles. Here, applying the piecewise polytropic equation of state for the neutron star matter and the equation of state of spin polarized self-interacting dark matter, we investigate the structure of neutron stars which are influenced by the spin polarized self-interacting dark matter. The behavior of the...

  20. Magnetic Switching of a Single Molecular Magnet due to Spin-Polarized Current

    OpenAIRE

    Misiorny, Maciej; Barnas, Józef

    2006-01-01

    Magnetic switching of a single molecular magnet (SMM) due to spin-polarized current flowing between ferromagnetic metallic electrodes is investigated theoretically. Magnetic moments of the electrodes are assumed to be collinear and parallel to the magnetic easy axis of the molecule. Electrons tunneling through a barrier between magnetic leads are coupled to the SMM via exchange interaction. The current flowing through the system as well as the spin relaxation times of the SMM are calculated f...

  1. Transport Properties of Spin-Polarized Atomic Hydrogen Using Generalized Scattering Theory

    Science.gov (United States)

    Joudeh, B. R.; Sandouqa, A. S.

    2018-02-01

    Our results for the scattering and thermophysical properties of spin-polarized atomic hydrogen (H{\\downarrow }) have been presented in the temperature range 0.01-10 K using the Galitskii-Migdal-Feynman formalism. These results include the quantum second virial coefficient, the average total and viscosity cross sections, the viscosity, the diffusion coefficient, and the thermal conductivity. The calculations have been undertaken using three triplet-state potentials: Morse-type, Silvera and Born-Oppenheimer potentials. The Morse potential is less attractive and very simple, but less accurate to describe spin-polarized atomic hydrogen. That explains the differences between it and the other two potentials, which are clearly better. From the results of the average total cross sections, it is concluded the H{\\downarrow } remains a gas even at low temperature. The viscosity, the thermal conductivity, and the diffusion coefficients of H{\\downarrow } increase in all cases with increasing temperature.

  2. High spin-polarization in ultrathin Co{sub 2}MnSi/CoPd multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Galanakis, I., E-mail: galanakis@upatras.gr

    2015-03-01

    Half-metallic Co{sub 2}MnSi finds a broad spectrum of applications in spintronic devices either in the form of thin films or as spacer in multilayers. Using state-of-the-art ab-initio electronic structure calculations we exploit the electronic and magnetic properties of ultrathin Co{sub 2}MnSi/CoPd multilayers. We show that these heterostructures combine high values of spin-polarization at the Co{sub 2}MnSi spacer with the perpendicular magnetic anisotropy of binary compounds such as CoPd. Thus they could find application in spintronic/magnetoelectronic devices. - Highlights: • Ab-initio study of ultrathin Co{sub 2}MnSi/CoPd multilayers. • Large values of spin-polarization at the Fermi are retained. • Route for novel spintronic/magnetoelectronic devices.

  3. High-frequency dynamics of spin-polarized carriers and photons in a laser

    Science.gov (United States)

    Saha, D.; Basu, D.; Bhattacharya, P.

    2010-11-01

    The high-frequency dynamics of spin-polarized carriers and photons in a spin laser have been studied. The transient response of the device obtained from the rate equations is characterized by two sets of relaxation oscillations in the carrier and photon distributions corresponding to the two polarization modes. Consequently two distinct resonant peaks are observed in the small-signal modulation response. The calculated transient characteristics indicate that the best results are obtained from a spin laser when only the favored polarization mode, with lower threshold, is operational. Under this condition the small-signal modulation bandwidth is higher than that in a conventional laser, the threshold current is lower and the output polarization can be 100% with appropriate bias conditions, independent of the spin polarization of carriers in the active region. Measurements were made at 230 K on a InAs/GaAs quantum dot spin vertical cavity surface emitting laser. A time-averaged output polarization of 55% is measured with an active region spin polarization of 5-6% . The experimental results are in good agreement with calculated data.

  4. Spin polarized Auger electron spectroscopy of Fe and Ni

    Science.gov (United States)

    Anilturk, O. S.; Koymen, A. R.

    2001-06-01

    Surface sensitive experiments, in which the spin-polarized electrons are involved, play an important role for magnetic characterization, since the spin-polarized electrons are fingerprints for the local magnetization. Scanning electron microscope with polarization analysis (SEMPA) is one of the most powerful tools to investigate the surface magnetic domain structure of magnetic materials. On the other hand, at energies high enough to generate a two-hole final state arising from Auger transitions, it is possible to observe the spin polarization of the Auger electrons. These electrons reveal element-specific local magnetic information, particularly valuable for surface magnetic studies with composite systems. By using the uniqueness of the UTA-SEMPA tool, one can obtain the magnetic domain picture and also perform spin-polarized Auger electron spectroscopy studies by probing a single domain at the surface. In this study, precisely knowing the probed domain, spin polarization of electrons from super Coster-Kronig MMM Auger emissions on Fe and Ni samples have been investigated. The polarization enhancement above the 3p(M23) threshold is observed on both samples.

  5. Spin polarized Auger electron spectroscopy of Fe and Ni

    International Nuclear Information System (INIS)

    Anilturk, O. S.; Koymen, A. R.

    2001-01-01

    Surface sensitive experiments, in which the spin-polarized electrons are involved, play an important role for magnetic characterization, since the spin-polarized electrons are fingerprints for the local magnetization. Scanning electron microscope with polarization analysis (SEMPA) is one of the most powerful tools to investigate the surface magnetic domain structure of magnetic materials. On the other hand, at energies high enough to generate a two-hole final state arising from Auger transitions, it is possible to observe the spin polarization of the Auger electrons. These electrons reveal element-specific local magnetic information, particularly valuable for surface magnetic studies with composite systems. By using the uniqueness of the UTA-SEMPA tool, one can obtain the magnetic domain picture and also perform spin-polarized Auger electron spectroscopy studies by probing a single domain at the surface. In this study, precisely knowing the probed domain, spin polarization of electrons from super Coster - Kronig MMM Auger emissions on Fe and Ni samples have been investigated. The polarization enhancement above the 3p(M 23 ) threshold is observed on both samples. [copyright] 2001 American Institute of Physics

  6. Observation of the spin-polarized surface state in a noncentrosymmetric superconductor BiPd.

    Science.gov (United States)

    Neupane, Madhab; Alidoust, Nasser; Hosen, M Mofazzel; Zhu, Jian-Xin; Dimitri, Klauss; Xu, Su-Yang; Dhakal, Nagendra; Sankar, Raman; Belopolski, Ilya; Sanchez, Daniel S; Chang, Tay-Rong; Jeng, Horng-Tay; Miyamoto, Koji; Okuda, Taichi; Lin, Hsin; Bansil, Arun; Kaczorowski, Dariusz; Chou, Fangcheng; Hasan, M Zahid; Durakiewicz, Tomasz

    2016-11-07

    Recently, noncentrosymmetric superconductor BiPd has attracted considerable research interest due to the possibility of hosting topological superconductivity. Here we report a systematic high-resolution angle-resolved photoemission spectroscopy (ARPES) and spin-resolved ARPES study of the normal state electronic and spin properties of BiPd. Our experimental results show the presence of a surface state at higher-binding energy with the location of Dirac point at around 700 meV below the Fermi level. The detailed photon energy, temperature-dependent and spin-resolved ARPES measurements complemented by our first-principles calculations demonstrate the existence of the spin-polarized surface states at high-binding energy. The absence of such spin-polarized surface states near the Fermi level negates the possibility of a topological superconducting behaviour on the surface. Our direct experimental observation of spin-polarized surface states in BiPd provides critical information that will guide the future search for topological superconductivity in noncentrosymmetric materials.

  7. Spin-polarized inelastic tunneling through insulating barriers.

    Science.gov (United States)

    Lu, Y; Tran, M; Jaffrès, H; Seneor, P; Deranlot, C; Petroff, F; George, J-M; Lépine, B; Ababou, S; Jézéquel, G

    2009-05-01

    Spin-conserving hopping transport through chains of localized states has been evidenced by taking benefit of the high degree of spin-polarization of CoFeB-MgO-CoFeB magnetic tunnel junctions. In particular, our data show that relatively thick MgO barriers doped with boron favor the activation of spin-conserving inelastic channels through a chain of three localized states and leading to reduced magnetoresistance effects. We propose an extension of the Glazman-Matveev theory to the case of ferromagnetic reservoirs to account for spin-polarized inelastic tunneling through nonmagnetic localized states embedded in an insulating barrier.

  8. Current-induced spin polarization in a spin-polarized two-dimensional electron gas with spin-orbit coupling

    International Nuclear Information System (INIS)

    Wang, C.M.; Pang, M.Q.; Liu, S.Y.; Lei, X.L.

    2010-01-01

    The current-induced spin polarization (CISP) is investigated in a combined Rashba-Dresselhaus spin-orbit-coupled two-dimensional electron gas, subjected to a homogeneous out-of-plane magnetization. It is found that, in addition to the usual collision-related in-plane parts of CISP, there are two impurity-density-free contributions, arising from intrinsic and disorder-mediated mechanisms. The intrinsic parts of spin polarization are related to the Berry curvature, analogous with the anomalous and spin Hall effects. For short-range collision, the disorder-mediated spin polarizations completely cancel the intrinsic ones and the total in-plane components of CISP equal those for systems without magnetization. However, for remote disorders, this cancellation does not occur and the total in-plane components of CISP strongly depend on the spin-orbit interaction coefficients and magnetization for both pure Rashba and combined Rashba-Dresselhaus models.

  9. Spin-polarized tunneling through a ferromagnetic insulator

    NARCIS (Netherlands)

    Kok, M.; Kok, M.; Beukers, J.N.; Brinkman, Alexander

    2009-01-01

    The polarization of the tunnel conductance of spin-selective ferromagnetic insulators is modeled, providing a generalized concept of polarization including both the effects of electrode and barrier polarization. The polarization model is extended to take additional non-spin-polarizing insulating

  10. Spin-polarized current generated by magneto-electrical gating

    International Nuclear Information System (INIS)

    Ma Minjie; Jalil, Mansoor Bin Abdul; Tan, Seng Ghee

    2012-01-01

    We theoretically study spin-polarized current through a single electron tunneling transistor (SETT), in which a quantum dot (QD) is coupled to non-magnetic source and drain electrodes via tunnel junctions, and gated by a ferromagnetic (FM) electrode. The I–V characteristics of the device are investigated for both spin and charge currents, based on the non-equilibrium Green's function formalism. The FM electrode generates a magnetic field, which causes a Zeeman spin-splitting of the energy levels in the QD. By tuning the size of the Zeeman splitting and the source–drain bias, a fully spin-polarized current is generated. Additionally, by modulating the electrical gate bias, one can effect a complete switch of the polarization of the tunneling current from spin-up to spin-down current, or vice versa. - Highlights: ► The spin polarized transport through a single electron tunneling transistor is systematically studied. ► The study is based on Keldysh non-equilibrium Green's function and equation of motion method. ► A fully spin polarized current is observed. ► We propose to reverse current polarization by the means of gate voltage modulation. ► This device can be used as a bi-polarization current generator.

  11. Fusion with highly spin polarized HD and D2

    International Nuclear Information System (INIS)

    Honig, A.

    1992-01-01

    This report discusses the following topics relating to inertial confinement with spin polarized hydrogen targets: low temperature implementation of mating a target to omega; dilution-refrigerator cold-entry and retrieval system; target shell tensile strength characterization at low temperatures; and proton and deuteron spin-lattice relaxation measurements in HD in the millikelvin temperature range

  12. Spin-Polarized Semiconductor Induced by Magnetic Impurities in Graphene

    OpenAIRE

    Daghofer, Maria; Zheng, Nan; Moreo, Adriana

    2010-01-01

    Magnetic impurities adsorbed on graphene are coupled magnetically via the itinerant electrons. This interaction opens a gap in the band structure of graphene. The result strongly depends on how the magnetic impurities are distributed. While random doping produces a semiconductor, if all or most impurities are located in the same sublattice, the spin degeneracy is removed and a spin-polarized semiconductor arises.

  13. Experiment on the melting pressure of spin polarized He3

    DEFF Research Database (Denmark)

    Chapellier, M.; Olsen, M.; Rasmussen, Finn Berg

    1981-01-01

    In liquid He in a Pomeranchuk cell, the melting curve has been observed to be suppressed, presumably in regions with a strong local spin polarization. In the temperature range 30-50 mK the observed suppression was 60-80 kPa. The corresponding local polarization is estimated, in a crude model, to ...

  14. Spin polarization effects in low-energy elastic electron scattering

    International Nuclear Information System (INIS)

    Beerlage, M.J.M.

    1982-01-01

    This work describes experiments on the role of spin polarization in elastic electron scattering. Chapter I introduces the topic and in chapter II elastic scattering of 10-50 eV electrons from Ar and Kr in the angular range between 40 0 and 110 0 is studied. Noble gases have been chosen as targets in view of their relative theoretical simplicity. Below 25 eV scattered intensities measured by various authors exhibit severe disagreements. However, in the entire energy range, the spin polarization results can reasonably well be used to point out the shortcomings of the available theoretical data. The main topic of chapter III is the first attempt to determine the magnitude of a polarization phenomenon - in elastic electron scattering from the optically active camphor molecule - of which the existence has recently been predicted qualitatively from the absence of parity symmetry in such molecules. Besides these studies on gaseous targets the author has initiated a scattering experiment on crystal surfaces, using spin polarized electrons. Within the framework of this project a large new experimental arrangement has been built up. It consists of a spin polarized electron source and a LEED scattering chamber. Design, construction and test results, showing the usefulness of the set-up, are described in the last chapter. (Auth.)

  15. Direct observation of hopping induced spin polarization current in oxygen deficient Co-doped ZnO by Andreev reflection technique

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Kung-Shang; Huang, Tzu-Yu; Dwivedi, G.D. [Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan (China); Lin, Lu-Kuei; Lee, Shang-Fan [Taiwan Institute of Physics, Academia Sinica, Taipei, Taiwan (China); Sun, Shih-Jye [Department of Applied Physics, National Kaohsiung University, Kaohsiung, Taiwan (China); Chou, Hsiung, E-mail: hchou@mail.nsysu.edu.tw [Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan (China)

    2017-07-01

    Highlights: • Co-doped ZnO thin-films were grown with varying V{sub O} concentartion. • PCAR measurements were done to study the SPC. • High spin polarization was observed above a certain V{sub O} concentartion. • High V{sub O} samples provide a high density of completed percolation path. • This complete percolation path gives rise to high SPC. - Abstract: Oxygen vacancy induced ferromagnetic coupling in diluted magnetic oxide (DMO) semiconductors have been reported in several studies, but technologically more crucial spin-polarized current (SPC) is still under-developed in DMOs. Few studies have claimed that VRH mechanism can originate the SPC, but, how VRH mechanism associated with percolation path, is not clearly understood. We used Point-contact Andreev reflection (PCAR) technique to probe the SPC in Co-doped ZnO (CZO) films. Since the high resistance samples cause broadening in conductance(G)-voltage(V) curves, which may result in an unreliable evaluation of spin polarization, we include two extra parameters, (i) effective temperature and (ii) spreading resistance, for the simulation to avoid the uncertainty in extracting spin polarization. The effective G-V curves and higher spin polarization can be obtained above a certain oxygen vacancy concentration. The number of completed and fragmentary percolation paths is proportional to the concentration of oxygen vacancies. For low oxygen vacancy samples, the Pb-tip has a higher probability of covering fragmentary percolation paths than the complete ones, due to its small contact size. The completed paths may remain independent of one another and get polarized in different directions, resulting in lower spin-polarization value. High oxygen vacancy samples provide a high density of completed path, most of them link to one another by crossing over, and gives rise to high spin-polarization value.

  16. Conductance and spin polarization for a quantum wire with the competition of Rashba and Dresselhaus spin-orbit coupling

    International Nuclear Information System (INIS)

    Fu Xi; Chen Zeshun; Zhong Feng; Zhou Guanghui

    2010-01-01

    We investigate theoretically the spin transport of a quantum wire (QW) with weak Rashba and Dresselhaus spin-orbit coupling (SOC) nonadiabatically connected to two normal leads. Using scattering matrix method and Landauer-Buettiker formula within effective free-electron approximation, we have calculated spin-dependent conductances G ↑ and G ↓ , total conductance G and spin polarization P z for a hard-wall potential confined QW. It is demonstrated that, the SOCs induce the splitting of G ↑ and G ↓ and form spin polarization P z . Moreover, the conductances present quantized plateaus, the plateaus and P z show oscillation structures near the subband edges. Furthermore, with the increase of QW width a strong spin polarization (P z ∼1) gradually becomes weak, which can be used to realize a spin filter. When the two SOCs coexist, the total conductance presents an isotropy transport due to the Rashba and Dresselhaus Hamiltonians being fixed, and the alteration of two SOCs strength ratio changes the sign of spin polarization. This may provide a way of realizing the expression of unit information by tuning gate voltage.

  17. Spin-polarized light-emitting diodes based on organic bipolar spin valves

    Energy Technology Data Exchange (ETDEWEB)

    Vardeny, Zeev Valentine; Nguyen, Tho Duc; Ehrenfreund, Eitan Avraham

    2017-10-25

    Spin-polarized organic light-emitting diodes are provided. Such spin-polarized organic light-emitting diodes incorporate ferromagnetic electrodes and show considerable spin-valve magneto-electroluminescence and magneto-conductivity responses, with voltage and temperature dependencies that originate from the bipolar spin-polarized space charge limited current.

  18. Universal spin-polarization fluctuations in one-dimensional wires with magnetic impurities

    DEFF Research Database (Denmark)

    Mortensen, Asger; Egues, J.C.

    2002-01-01

    -flip suppresses conductance fluctuations while enhancing spin-polarization fluctuations. More importantly, spin-polarization fluctuations attain a universal value 1/3 for large enough spin-flip strengths. This intrinsic spin-polarization fluctuation may pose a severe limiting factor to the realization of steady...

  19. Quantum properties of spin polarized helium 3 optically oriented by a LNA laser

    International Nuclear Information System (INIS)

    Leduc, M.; Laloe, F.; Nacher, P.J.; Tastevin, G.; Daniels, J.M.; Betts, D.

    1986-01-01

    Spin polarized helium 3 (/sup 3/He increasing) and also atomic hydrogen (H decreasing) are systems exhibiting a number of unusual and interesting properties at low temperature. This is true even for dilute polarized gases in spite of the weakness of the nuclear magnetic interaction between atoms. The changes in the macroscopic properties of the gas with the nuclear polarization P are pure consequences of the indistinguishability of the particles and of the symmetrization principle in quantum mechanics. The transport properties of the gas, such as viscosity and thermal conductivity, have been calculated and found to be strongly dependent on P below a few kelvins. Spin transport in /sup 3/He increasing gives rise at low temperature to collective oscillatory modes: the transverse spin waves. Large changes are also expected with P in the case of more dense /sup 3/He fluids, such as an increase with P in the saturated vapor pressure. Optical pumping is a convenient technique for efficient polarization of the nuclear spins in /sup 3/He gas/sup 2/ making use of the 2/sup 3/S-2/sup 3/P atomic line at 1.08 μm. The arrival of cw tunable lasers in the near IR in the early 1980s gave a strong impulse to the buildup of experiments with a view to measuring quantum properties of /sup 3/He increasing at low temperature. Color center lasers (F/sup +//sub 2/ in NaF) provide P values up to 70%. They are now being replaced by more easy to handle LNA lasers which have given so far P in excess of 50% at room temperature. At low temperature, direct optical pumping of a /sup 3/He cell leads to poor P values; for that reason a different technique is used

  20. Measuring the spin polarization of alkali-metal atoms using nuclear magnetic resonance frequency shifts of noble gases

    Directory of Open Access Journals (Sweden)

    X. H. Liu

    2015-10-01

    Full Text Available We report a novel method of measuring the spin polarization of alkali-metal atoms by detecting the NMR frequency shifts of noble gases. We calculated the profile of 87Rb D1 line absorption cross sections. We then measured the absorption profile of the sample cell, from which we calculated the 87Rb number densities at different temperatures. Then we measured the frequency shifts resulted from the spin polarization of the 87Rb atoms and calculated its polarization degrees at different temperatures. The behavior of frequency shifts versus temperature in experiment was consistent with theoretical calculation, which may be used as compensative signal for the NMRG closed-loop control system.

  1. Physical processes in spin polarized plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Kulsrud, R.M.; Valeo, E.J.; Cowley, S.

    1984-05-01

    If the plasma in a nuclear fusion reactor is polarized, the nuclear reactions are modified in such a way as to enhance the reactor performance. We calculate in detail the modification of these nuclear reactions by different modes of polarization of the nuclear fuel. We also consider in detail the various physical processes that can lead to depolarization and show that they are by and large slow enough that a high degree of polarization can be maintained.

  2. Widespread spin polarization effects in photoemission from topological insulators

    Energy Technology Data Exchange (ETDEWEB)

    Jozwiak, C.; Chen, Y. L.; Fedorov, A. V.; Analytis, J. G.; Rotundu, C. R.; Schmid, A. K.; Denlinger, J. D.; Chuang, Y.-D.; Lee, D.-H.; Fisher, I. R.; Birgeneau, R. J.; Shen, Z.-X.; Hussain, Z.; Lanzara, A.

    2011-06-22

    High-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi{sub 2}Se{sub 3} using a recently developed high-efficiency spectrometer. The topological surface state's helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations of photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.

  3. Tilted Foils Nuclear Spin Polarization at REX-ISOLDE

    CERN Document Server

    Törnqvist, Hans Toshihide

    2013-08-08

    This thesis will explain and summarize my work and involvement in experiments aimed at producing nuclear spin polarization of post-accelerated beams of ions with the tilted-foils technique at the REX-ISOLDE linear accelerator at CERN. Polarizing the nuclear spin of radioactive beams in particular may provide access to observables which may be difficult to obtain otherwise. Currently, the techniques commonly employed for nuclear spin polarization are restricted to specific nuclides and experimental measurement techniques. Tilted foils polarization may provide a new tool to extend the range of nuclides that can be polarized and the types of experiments that can be performed. The experiments rely not only on the production but also on the method to measure the degree of attained polarization. Two methods will be treated, based on particle scattering in Coulomb excitation that may be utilized for stable beams, and the $\\beta$-NMR that requires $\\beta$-decaying nuclei. The experimental setups and measurements will...

  4. Engineering the spin polarization of one-dimensional electrons

    Science.gov (United States)

    Yan, C.; Kumar, S.; Thomas, K.; See, P.; Farrer, I.; Ritchie, D.; Griffiths, J.; Jones, G.; Pepper, M.

    2018-02-01

    We present results of magneto-focusing on the controlled monitoring of spin polarization within a one-dimensional (1D) channel, and its subsequent effect on modulating the spin–orbit interaction (SOI) in a 2D GaAs electron gas. We demonstrate that electrons within a 1D channel can be partially spin polarized as the effective length of the 1D channel is varied in agreement with the theoretical prediction. Such polarized 1D electrons when injected into a 2D region result in a split in the odd-focusing peaks, whereas the even peaks remain unaffected (single peak). On the other hand, the unpolarized electrons do not affect the focusing spectrum and the odd and even peaks remain as single peaks, respectively. The split in odd-focusing peaks is evidence of direct measurement of spin polarization within a 1D channel, where each sub-peak represents the population of a particular spin state. Confirmation of the spin splitting is determined by a selective modulation of the focusing peaks due to the Zeeman energy in the presence of an in-plane magnetic field. We suggest that the SOI in the 2D regime is enhanced by a stream of polarized 1D electrons. The spatial control of spin states of injected 1D electrons and the possibility of tuning the SOI may open up a new regime of spin-engineering with application in future quantum information schemes.

  5. Non-dipole effects in spin polarization of photoelectrons from 3d electrons of Xe, Cs and Ba

    Energy Technology Data Exchange (ETDEWEB)

    Amusia, M Ya [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Cherepkov, N A [State University of Aerospace Instrumentation, St. Petersburg 190000 (Russian Federation); Chernysheva, L V [A F Ioffe Physical-Technical Institute, St. Petersburg 194021 (Russian Federation); Felfli, Z [Department of Physics and Center for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta GA 30314 (United States); Msezane, A Z [Department of Physics and Center for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta GA 30314 (United States)

    2005-04-28

    The non-dipole contribution to spin polarization of photoelectrons from Xe, Cs and Ba 3d{sub 5/2} and 3d{sub 3/2} levels is calculated. The calculation is carried out within the framework of a modified version of the spin-polarized random phase approximation with exchange. The effects of relaxation of excited electrons due to the 3d-vacancy creation are also accounted for. It is demonstrated that the parameters that characterize the photoelectron angular distribution as functions of the incoming photon energy, although being predictably small, acquire additional peculiarities when the interaction between electrons that belong to the 3d{sub 5/2} and 3d{sub 3/2} components of the spin-orbit doublet is taken into account.

  6. Interface-induced chiral domain walls, spin spirals and skyrmions revealed by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    von Bergmann, Kirsten; Kubetzka, André; Pietzsch, Oswald; Wiesendanger, Roland

    2014-10-01

    The spin textures of ultra-thin magnetic layers exhibit surprising variety. The loss of inversion symmetry at the interface of the magnetic layer and substrate gives rise to the so-called Dzyaloshinskii-Moriya interaction which favors non-collinear spin arrangements with unique rotational sense. Here we review the application of spin-polarized scanning tunneling microscopy to such systems, which has led to the discovery of interface-induced chiral domain walls and spin spirals. Recently, different interface-driven skyrmion lattices have been found, and the writing as well as the deleting of individual skyrmions based on local spin-polarized current injection has been demonstrated. These interface-induced non-collinear magnetic states offer new exciting possibilities to study fundamental magnetic interactions and to tailor material properties for spintronic applications.

  7. Electron-spin polarization in tunnel junctions with ferromagnetic EuS barriers

    International Nuclear Information System (INIS)

    Hao, X.; Moodera, J.S.; Meservey, R.

    1989-01-01

    The authors report here spin-polarized tunneling experiments using non-ferromagnetic electrodes and ferromagnetic EuS barriers. Because of the conduction band in EuS splits into spin-up and spin-down subbands when the temperature is below 16.7 K, the Curie temperature of EuS, the tunnel barrier for electrons with different spin directions is different, therefore giving rise to tunnel current polarization. The spin-filter effect, as it may be called, was observed earlier, directly or indirectly, by several groups: Esaki et al. made a tunneling study on junctions having EuS and EuSe barriers; Thompson et al. studied Schottky barrier tunneling between In and doped EuS; Muller et al. and Kisker et al. performed electron field emission experiments on EuS-coated tungsten tips. The field emission experiments gave a maximum polarization of (89 + 7)% for the emitted electrons. Although the previous tunneling studies did not directly show electron polarization, their results were explained by the same spin- filter effect. This work uses the spin-polarized tunneling technique to show directly that tunnel current is indeed polarized and polarization can be as high as 85%

  8. Multispin-assisted optical pumping of bulk 13C nuclear spin polarization in diamond

    Science.gov (United States)

    Pagliero, Daniela; Rao, K. R. Koteswara; Zangara, Pablo R.; Dhomkar, Siddharth; Wong, Henry H.; Abril, Andrea; Aslam, Nabeel; Parker, Anna; King, Jonathan; Avalos, Claudia E.; Ajoy, Ashok; Wrachtrup, Joerg; Pines, Alexander; Meriles, Carlos A.

    2018-01-01

    One of the most remarkable properties of the nitrogen-vacancy (NV) center in diamond is that optical illumination initializes its electronic spin almost completely, a feature that can be exploited to polarize other spin species in their proximity. Here we use field-cycled nuclear magnetic resonance to investigate the mechanisms of spin-polarization transfer from NVs to 13C spins in diamond at room temperature. We focus on the dynamics near 51 mT, where a fortuitous combination of energy-matching conditions between electron and nuclear spin levels gives rise to alternative polarization transfer channels. By monitoring the 13C spin polarization as a function of the applied magnetic field, we show 13C spin pumping takes place via a multispin cross-relaxation process involving the N V- spin and the electronic and nuclear spins of neighboring P1 centers. Further, we find that this mechanism is insensitive to the crystal orientation relative to the magnetic field, although the absolute level of 13C polarization—reaching up to ˜3 % under optimal conditions—can vary substantially depending on the interplay between optical pumping efficiency, photogenerated carriers, and laser-induced heating.

  9. Enhancing current-induced torques by abutting additional spin polarizer layer to nonmagnetic metal layer

    Science.gov (United States)

    Go, Gyungchoon; Lee, Kyung-Jin; Kim, Young Keun

    2017-04-01

    Recently, the switching of a perpendicularly magnetized ferromagnet (FM) by injecting an in-plane current into an attached non-magnet (NM) has become of emerging technological interest. This magnetization switching is attributed to the spin-orbit torque (SOT) originating from the strong spin-orbit coupling of the NM layer. However, the switching efficiency of the NM/FM structure itself may be insufficient for practical use, as for example, in spin transfer torque (STT)-based magnetic random access memory (MRAM) devices. Here we investigate spin torque in an NM/FM structure with an additional spin polarizer (SP) layer abutted to the NM layer. In addition to the SOT contribution, a spin-polarized current from the SP layer creates an extra spin chemical potential difference at the NM/FM interface and gives rise to a STT on the FM layer. We show that, using typical parameters including device width, thickness, spin diffusion length, and the spin Hall angle, the spin torque from the SP layer can be much larger than that from the spin Hall effect (SHE) of the NM.

  10. Partial spin polarization of a conductance in a bi-layer In0.52 Al0.48 As / In0.53 Ga0.47 As heterostructure based nanowire for the rectangular and the smooth lateral confinement potentials

    Science.gov (United States)

    Chwiej, T.

    2016-03-01

    We simulate the electron transport in a vertical bi-layer nanowire in order to study an influence of the lateral confinement's shape on a spin polarization of wire's conductance. The active part of considered quantum wire constitutes a double inverted heterojunction In0.52 Al0.48 As /In0.53 Ga0.47 As which nanostructure can be fabricated in molecular beam epitaxy process while the lateral confinement potential can be finally formed by means of cleaved overgrowth or surface oxidization methods giving the desired rectangular and smooth lateral confinement. In calculations we take into account interaction between charge carriers using DFT within local spin density approximation. We show that if the magnetic field is perpendicular to the wire axis, the pseudogaps are opened in energy dispersion relation E (k) what in conjunction with spin Zeeman shift of spin-up and spin-down subbands may enhance the spin polarization of conductance with reference to a single layer wire. For nanowire with rectangular lateral confinement potential we found that the electron density has two maximums localized at wire edges in each layers. This modificates strongly all magnetosubbands giving up to four energy minimums in lowest subband and considerably diminishes widths of pseudogaps what translates into low maximal spin polarization of conductance, not exceeding 40%. This drawback is absent in wire with smooth lateral confinement. However, in order to gain a large spin polarization simultaneous tuning of magnetic field as well as the Fermi energies in both layers of nanowire are required.

  11. Antiferromagnetic Spin Coupling between Rare Earth Adatoms and Iron Islands Probed by Spin-Polarized Tunneling.

    Science.gov (United States)

    Coffey, David; Diez-Ferrer, José Luis; Serrate, David; Ciria, Miguel; de la Fuente, César; Arnaudas, José Ignacio

    2015-09-03

    High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths.

  12. Generalized nuclear Fukui functions in the framework of spin-polarized density-functional theory

    International Nuclear Information System (INIS)

    Chamorro, E.; Proft, F. de; Geerlings, P.

    2005-01-01

    An extension of Cohen's nuclear Fukui function is presented in the spin-polarized framework of density-functional theory (SP-DFT). The resulting new nuclear Fukui function indices Φ Nα and Φ Sα are intended to be the natural descriptors for the responses of the nuclei to changes involving charge transfer at constant multiplicity and also the spin polarization at constant number of electrons. These generalized quantities allow us to gain new insights within a perturbative scheme based on DFT. Calculations of the electronic and nuclear SP-DFT quantities are presented within a Kohn-Sham framework of chemical reactivity for a sample of molecules, including H 2 O, H 2 CO, and some simple nitrenes (NX) and phosphinidenes (PX), with X=H, Li, F, Cl, OH, SH, NH 2 , and PH 2 . Results have been interpreted in terms of chemical bonding in the context of Berlin's theorem, which provides a separation of the molecular space into binding and antibinding regions

  13. New materials research for high spin polarized current

    International Nuclear Information System (INIS)

    Tezuka, Nobuki

    2012-01-01

    The author reports here a thorough investigation of structural and magnetic properties of Co 2 FeAl 0.5 Si 0.5 Heusler alloy films, and the tunnel magnetoresistance effect for junctions with Co 2 FeAl 0.5 Si 0.5 electrodes, spin injection into GaAs semiconductor from Co 2 FeAl 0.5 Si 0.5 , and spin filtering phenomena for junctions with CoFe 2 O 4 ferrite barrier. It was observed that tunnel magnetoresistance ratio up to 832%(386%) at 9 K (room temperature), which corresponds to the tunnel spin polarization of 0.90 (0.81) for the junctions using Co 2 FeAl 0.5 Si 0.5 Heusler electrodes by optimizing the fabrication condition. It was also found that the tunnel magnetoresistance ratio are almost the same between the junctions with Co 2 FeAl 0.5 Si 0.5 Heusler electrodes on Cr buffered (1 0 0) and (1 1 0) MgO substrates, which indicates that tunnel spin polarization of Co 2 FeAl 0.5 Si 0.5 for these two direction are almost the same. The next part of this paper is a spin filtering effect using a Co ferrite. The spin filtering effect was observed through a thin Co-ferrite barrier. The inverse type tunnel magnetoresistance ratio of −124% measured at 10 K was obtained. The inverse type magnetoresistance suggests the negative spin polarization of Co-ferrite barrier. The magnetoresistance ratio of −124% corresponds to the spin polarization of −0.77 by the Co-ferrite barrier. The last part is devoted to the spin injection from Co 2 FeAl 0.5 Si 0.5 into GaAs. The spin injection signal was clearly obtained by three terminal Hanle measurement. The spin relaxation time was estimated to be 380 ps measured at 5 K.

  14. Spin-polarization of an electro-static positron beam

    International Nuclear Information System (INIS)

    Kawasuso, A.; Maekawa, M.

    2008-01-01

    We constructed an electro-static positron beam apparatus. We fabricated a simple spin-polarimeter composed of a permanent magnet with a surface magnetic field of 0.65 T and an iron pole piece. The longitudinal spin-polarization of the positron beam was determined to be 0.3 by analyzing the magnetic field dependence of the Doppler broadening of annihilation radiation from a fused silica specimen. The effect of spin rotation was examined using an iron poly-crystal and a simple E x B filter

  15. Effect of Rashba and Dresselhaus Spin-Orbit Couplings on Electron Spin Polarization in a Hybrid Magnetic-Electric Barrier Nanostructure

    Science.gov (United States)

    Yang, Shi-Peng; Lu, Mao-Wang; Huang, Xin-Hong; Tang, Qiang; Zhou, Yong-Long

    2017-04-01

    A theoretical study has been carried out on the spin-dependent electron transport in a hybrid magnetic-electric barrier nanostructure with both Rashba and Dresselhaus spin-orbit couplings, which can be experimentally realized by depositing a ferromagnetic strip and a Schottky metal strip on top of a semiconductor heterostructure. The spin-orbit coupling-dependent transmission coefficient, conductance, and spin polarization are calculated by solving the Schrödinger equation exactly with the help of the transfer-matrix method. We find that both the magnitude and sign of the electron spin polarization vary strongly with the spin-orbit coupling strength. Thus, the degree of electron spin polarization can be manipulated by properly adjusting the spin-orbit coupling strength, and such a nanosystem can be employed as a controllable spin filter for spintronics applications.

  16. The effects of Rashba spin-orbit coupling on spin-polarized transport in hexagonal graphene nano-rings and flakes

    Science.gov (United States)

    Laghaei, M.; Heidari Semiromi, E.

    2018-03-01

    Quantum transport properties and spin polarization in hexagonal graphene nanostructures with zigzag edges and different sizes were investigated in the presence of Rashba spin-orbit interaction (RSOI). The nanostructure was considered as a channel to which two semi-infinite armchair graphene nanoribbons were coupled as input and output leads. Spin transmission and spin polarization in x, y, and z directions were calculated through applying Landauer-Buttiker formalism with tight binding model and the Green's function to the system. In these quantum structures it is shown that changing the size of system, induce and control the spin polarized currents. In short, these graphene systems are typical candidates for electrical spintronic devices as spin filtering.

  17. Spin polarization driven by a charge-density wave in monolayer 1T−TaS2

    KAUST Repository

    Zhang, Qingyun

    2014-08-06

    Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer T-phase TaS2. We demonstrate that a charge-density wave is energetically favorable at low temperature, similar to bulk 1T-TaS2. Electron-phonon coupling is found to be essential for the lattice reconstruction. The charge-density wave results in a strong localization of the electronic states near the Fermi level and consequently in spin polarization, transforming the material into a magnetic semiconductor with enhanced electronic correlations. The combination of inherent spin polarization with a semiconducting nature distinguishes the monolayer fundamentally from the bulk compound as well as from other two-dimensional transition metal dichalcogenides. Monolayer T-phase TaS2 therefore has the potential to enable two-dimensional spintronics. © 2014 American Physical Society.

  18. Electron-Spin Filters Would Offer Spin Polarization Greater than 1

    Science.gov (United States)

    Ting, David Z.

    2009-01-01

    A proposal has been made to develop devices that would generate spin-polarized electron currents characterized by polarization ratios having magnitudes in excess of 1. Heretofore, such devices (denoted, variously, as spin injectors, spin polarizers, and spin filters) have typically offered polarization ratios having magnitudes in the approximate range of 0.01 to 0.1. The proposed devices could be useful as efficient sources of spin-polarized electron currents for research on spintronics and development of practical spintronic devices.

  19. Interplay between spin polarization and color superconductivity in high density quark matter

    DEFF Research Database (Denmark)

    Tsue, Yasuhiko; da Providência, João; Providência, Constança

    2013-01-01

    Here, it is suggested that a four-point interaction of the tensor type may lead to spin polarization in quark matter at high density. It is found that the two-flavor superconducting phase and the spin polarized phase correspond to distinct local minima of a certain generalized thermodynamical...... potential. It follows that a transition from one to the other phase occurs, passing through true minima with both a spin polarization and a color superconducting gap. It is shown that the quark spin polarized phase is realized at rather high density, while the two-flavor color superconducting phase...

  20. RKKY interaction for the spin-polarized electron gas

    Science.gov (United States)

    Valizadeh, Mohammad M.; Satpathy, Sashi

    2015-11-01

    We extend the original work of Ruderman, Kittel, Kasuya and Yosida (RKKY) on the interaction between two magnetic moments embedded in an electron gas to the case where the electron gas is spin-polarized. The broken symmetry of a host material introduces the Dzyaloshinsky-Moriya (DM) vector and tensor interaction terms, in addition to the standard RKKY term, so that the net interaction energy has the form ℋ = JS1 ṡS2 + D ṡS1 ×S2 + S1 ṡΓ ↔ṡS2. We find that for the spin-polarized electron gas, a nonzero tensor interaction Γ ↔ is present in addition to the scalar RKKY interaction J, while D is zero due to the presence of inversion symmetry. Explicit expressions for these are derived for the electron gas both in 2D and 3D and we show that the net magnetic interaction can be expressed as a sum of Heisenberg and Ising like terms. The RKKY interaction exhibits a beating pattern, caused by the presence of the two Fermi momenta kF↑ and kF↓, while the R-3 distance dependence of the original RKKY result for the 3D electron gas is retained. This model serves as a simple example of the magnetic interaction in systems with broken symmetry, which goes beyond the RKKY interaction.

  1. The impact of structural relaxation on spin polarization and magnetization reversal of individual nano structures studied by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Sander, Dirk; Phark, Soo-Hyon; Corbetta, Marco; Fischer, Jeison A; Oka, Hirofumi; Kirschner, Jürgen

    2014-10-01

    The application of low temperature spin-polarized scanning tunneling microscopy and spectroscopy in magnetic fields for the quantitative characterization of spin polarization, magnetization reversal and magnetic anisotropy of individual nano structures is reviewed. We find that structural relaxation, spin polarization and magnetic anisotropy vary on the nm scale near the border of a bilayer Co island on Cu(1 1 1). This relaxation is lifted by perimetric decoration with Fe. We discuss the role of spatial variations of the spin-dependent electronic properties within and at the edge of a single nano structure for its magnetic properties.

  2. Reconstruction of mono-vacancies in carbon nanotubes: Atomic relaxation vs. spin polarization

    International Nuclear Information System (INIS)

    Berber, S.; Oshiyama, A.

    2006-01-01

    We have investigated the reconstruction of mono-vacancies in carbon nanotubes using density functional theory (DFT) geometry optimization and electronic structure calculations, employing a numerical basis set. We considered mono-vacancies in achiral nanotubes with diameter range ∼4-9A. Contrary to previous tight-binding calculations, our results indicate that mono-vacancies could have several metastable geometries, confirming the previous plane-wave DFT results. Formation energy of mono-vacancies is 4.5-5.5eV, increasing with increasing tube diameter. Net magnetic moment decreases from ideal mono-vacancy value after reconstruction, reflecting the reduction of the number of dangling bonds. In spite of the existence of a dangling bond, ground state of mono-vacancies in semiconducting tubes have no spin polarization. Metallic carbon nanotubes show net magnetic moment for most stable structure of mono-vacancy, except for very small diameter tubes

  3. Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Menchero, Jose Gabriel [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

    In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.

  4. Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green's functions

    DEFF Research Database (Denmark)

    De Souza, Fabricio; Jauho, Antti-Pekka; Egues, J.C.

    2008-01-01

    Using nonequilibrium Green's functions we calculate the spin-polarized current and shot noise in a ferromagnet-quantum-dot-ferromagnet system. Both parallel (P) and antiparallel (AP) magnetic configurations are considered. Coulomb interaction and coherent spin flip (similar to a transverse magnet...

  5. Modeling optically pumped NMR and spin polarization in GaAs/AlGaAs quantum wells

    Science.gov (United States)

    Saha, D.; Wood, R.; Tokarski, J. T.; McCarthy, L. A.; Bowers, C. R.; Sesti, E. L.; Hayes, S. E.; Kuhns, P. L.; McGill, S. A.; Reyes, A. R.; Sanders, G. D.; Stanton, C. J.

    2014-08-01

    Optically-pumped nuclear magnetic resonance (OPNMR) spectroscopy is an emerging technique to probe electronic and nuclear spin properties in bulk and quantum well semiconductors. In OPNMR, one uses optical pumping with light to create spin-polarized electrons in a semiconductor. The electron spin can be transferred to the nuclear spin bath through the Fermi contact hyperfine interaction which can then be detected by conventional NMR. The resulting NMR signal can be enhanced four to five orders of magnitude or more over the thermal equilibrium signal. In previous work, we studied OPNMR in bulk GaAs where we investigated the strength of the OPNMR signal as a function of the pump laser frequency. This allowed us to study the spin-split valence band. Here we report on OPNMR studies in GaAs/AlGaAs quantum wells. We focus on theoretical calculations for the average electron spin polarization at different photon energies for different values of external magnetic field in both unstrained and strained quantum wells. Our calculations allow us to identify the Landau level transitions which are responsible for the peaks in the photon energy dependence of the OPNMR signal intensity. The calculations are based on the 8- band Pidgeon-Brown model generalized to include the effects of the quantum confinement potential as well as pseudomorphic strain at the interfaces. Optical properties are calculated within the golden rule approximation. Detailed comparison to experiment allows one to accurately determine valence band spin splitting in the quantum wells including the effects of strain.

  6. Spin-polarized relativistic linear-muffin-tin-orbital method: Volume-dependent electronic structure and magnetic moment of plutonium

    International Nuclear Information System (INIS)

    Solovyev, I.V.; Liechtenstein, A.I.; Gubanov, V.A.; Antropov, V.P.; Andersen, O.K.

    1991-01-01

    The linear-muffin-tin-orbital method is generalized to the case of relativistic and spin-polarized self-consistent band calculations. Our formalism is analogous to the standard orthogonal--linear-muffin-tin-orbital formalism, except that the potential functions and the potential parameters are now matrices. The method is used to perform density-functional calculations for fcc plutonium with different atomic volumes. The formation of spin and orbital magnetic moments, as well as the changes in the energy bands for volume changes corresponding to the α-δ transition, are investigated. The calculated magnetic moments agree quite well with the experimental ones

  7. Resonant tunneling via spin-polarized barrier states in a magnetic tunnel junction

    NARCIS (Netherlands)

    Jansen, R.; Lodder, J.C.

    2000-01-01

    Resonant tunneling through states in the barrier of a magnetic tunnel junction has been analyzed theoretically for the case of a spin-polarized density of barrier states. It is shown that for highly spin-polarized barrier states, the magnetoresistance due to resonant tunneling is enhanced compared

  8. Direct injection of spin-polarized carriers across YBa 2 Cu 3 O 7- ...

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 58; Issue 5-6. Direct injection of spin-polarized ... from the CMR layer is 38 mA. This clearly shows that spin-polarized quasiparticles injected from the CMR layer into the YBCO layer suppress the critical current of the superconductor via the pair-breaking phenomena.

  9. Laser driven source of spin polarized atomic deuterium and hydrogen

    International Nuclear Information System (INIS)

    Poelker, M.; Coulter, K.P.; Holt, R.J.

    1993-01-01

    Optical pumping of potassium atoms in the presence of a high magnetic field followed by spin exchange collisions with deuterium (hydrogen) is shown to yield a high flux of spin polarized atomic deuterium (hydrogen). The performance of the laser driven source has been characterized as a function of deuterium (hydrogen) flow rate, potassium density, pump laser power, and magnetic field. Under appropriate conditions, the authors have observed deuterium atomic polarization as high as 75% at a flow rate 4.2x10 17 atoms/second. Preliminary results suggest that high nuclear polarizations are obtained in the absence of weak field rf transitions as a result of a spin temperature distribution that evolves through frequent H-H (D-D) collisions

  10. ESR and related experiments in spin-polarized atomic hydrogen

    International Nuclear Information System (INIS)

    Yperen, G.H. van.

    1984-01-01

    This thesis deals with some experiments in (gaseous) spin-polarized atomic hydrogen. One uses the expression 'stabilized' atomic hydrogen, meaning that by choosing suitable conditions one can suppress the tendency of atoms to recombine into H 2 molecules, such that the lifetime of the atomic state is extended by many orders of magnitude. Research is focused at the study of processes that determine the decay rate of polarized H samples, with the ultimate goal of preparing samples of sufficiently high density and at low enough temperature to observe experimentally the behaviour of the (degenerate) quantum gas. ESR (Electron Spin Resonance) appears to be a very suitable measurement technique to study the properties of polarized H. This work describes the introduction of ESR as detection technique, and the first results of an experiment in polarized H using this technique. (orig.)

  11. Induced spin polarization effect in graphene by ferromagnetic nanocontact

    Energy Technology Data Exchange (ETDEWEB)

    Mandal, Sumit; Saha, Shyamal K., E-mail: cnssks@iacs.res.in [Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

    2015-03-07

    Chemically synthesized graphene contains large number of defects which act as localized spin moments at the defect sites. Cobalt nanosheets of variable thickness are grown on graphene surface to investigate spin/magnetotransport through graphene sheets containing large number of localized spins. Negative magnetoresistance (MR) is observed over the entire temperature range (5–300 K) for thin cobalt sheets, while a cross-over from negative to positive MR with increasing temperature is noticed for thicker cobalt sheets. The observed MR results are explained on the basis of recently reported spin polarization effect in graphene due to the presence of ferromagnetic atoms on the surface considering a spin valve like Co/graphene/Co nanostructures.

  12. Magnetic switching of a single molecular magnet due to spin-polarized current

    Science.gov (United States)

    Misiorny, Maciej; Barnaś, Józef

    2007-04-01

    Magnetic switching of a single molecular magnet (SMM) due to spin-polarized current flowing between ferromagnetic metallic leads (electrodes) is investigated theoretically. Magnetic moments of the leads are assumed to be collinear and parallel to the magnetic easy axis of the molecule. Electrons tunneling through the barrier between magnetic leads are coupled to the SMM via exchange interaction. The current flowing through the system, as well as the spin relaxation times of the SMM, are calculated from the Fermi golden rule. It is shown that spin of the SMM can be reversed by applying a certain voltage between the two magnetic electrodes. Moreover, the switching may be visible in the corresponding current-voltage characteristics.

  13. Confinement effect on spin-polarized edge states in graphene nanostructures

    Science.gov (United States)

    Ramos-Castillo, Carlos; de Coss, Romeo

    2014-03-01

    One of the most intriguing phenomena in condensed matter physics is the existence of edge states on the boundary of a 2D system. In graphene, the edge states have distinct properties from the bulk states and play important roles in the physicochemical properties of the material. In this work, we show ab-initio results of spin-polarized electronic edge states in graphene quantum dots of different sizes and shape. We found a critical size at which the singlet nonmagnetic ground state becomes singlet open-shell with antiferromagnetic order. We found that the critical size is strongly influenced by the shape of the quantum dot. We discuss this behavior based on energetics and electronic structure of the system under study. The calculations are base on the Density functional Theory (DFT). The Linear Combination of Atomic Orbital (LCAO) method for bases functions it was used. For exchange-correlation functional has been used the Generalized Gradient Approximation (GGA).

  14. Optically pumped electron spin polarized targets for use in the production of polarized ion beams

    International Nuclear Information System (INIS)

    Anderson, L.W.

    1979-01-01

    The production of relatively dense electron spin polarized alkali metal vapor targets by optical pumping with intense cw dye lasers is discussed. The target density and electron spin polarization depend on the dye laser intensity and bandwidth, the magnetic field at the target, and the electron spin depolarization time. For example in a magnetic field of 1.5 x 10 3 G, and using 1 W dye laser with a bandwidth of 10 10 Hz one can construct an electron spin polarized Na vapor target with a target thickness of 1.6 x 10 13 atoms/cm 2 and an average electron spin polarization of about 90% even though the Na atoms are completely depolarized at every wall collision. Possible uses of the electron spin polarized targets for the production of intense beams of polarized H - or 3 He - ions are discussed. (orig.)

  15. Electron ionization and spin polarization control of Fe atom adsorbed graphene irradiated by a femtosecond laser

    International Nuclear Information System (INIS)

    Yu, Dong; Jiang, Lan; Wang, Feng; Li, Xin; Qu, Liangti; Lu, Yongfeng

    2015-01-01

    We investigate the structural properties and ionized spin electrons of an Fe–graphene system, in which the time-dependent density functional theory (TDDFT) within the generalized gradient approximation is used. The electron dynamics, including electron ionization and ionized electron spin polarization, is described for Fe atom adsorbed graphene under femtosecond laser irradiation. The theoretical results show that the electron ionization and ionized electron spin polarization are sensitive to the laser parameters, such as the incident angle and the peak intensity. The spin polarization presents the maximum value under certain laser parameters, which may be used as a source of spin-polarized electrons. - Highlights: • The structural properties of Fe–graphene system are investigated. • The electron dynamics of Fe–graphene system under laser irradiation are described. • The Fe–graphene system may be used as a source of spin-polarized electrons

  16. New directions in the theory of spin-polarized atomic hydrogen and deuterium

    International Nuclear Information System (INIS)

    Koelman, J.M.V.A.

    1988-01-01

    The three chapters of this thesis dealing with collisions between hydrogen (or deuterium) atoms in their ground state, each treat a different development in the theory of atomic hydrogen or deuterium gas. The decay due to interatomic collisions hindered till now all attempts to reach the low temperature, high-density regime where effects due to degeneracy are expected to show up. In ch. 2 a simple way out is presented for the case of Fermi gases: In spin-polarized Fermi systems at very low temperatures collisions are much effective than in Bose systems. For the Fermi gas, consisting of magnetically confined deuterium atoms, it appears that fast spin-exchange collisions automatically lead to a completely spin-polarized gas for which the spin-relaxation limited lifetime increases dramatically with decreasing temperature. As also the ratio of internal thermalization rate over decay rate increases with decreasing temperature, this gas can be cooled by forced evaporation down to very low temperatures. In ch. 3 it iis shown that the nuclear spin dynamics due to the hyperfine interaction during collisions, strongly limits the improvement in frequency stability attainable by H masers operating at low temperatures. In ch. 4 the phenomenon of spin waves is studied. It is shown that, despite the fact that interactions between two atoms are nuclear-spin independent, the outcome of a scattering event does not depend on the nuclear spins involved due to the particle indistinguishability effects at low collision energies. This effect gives rise to quantum phenomena on a macroscopic scale via the occurrence of spin waves. (author). 185 refs.; 34 figs

  17. TOPICAL REVIEW: Highly spin-polarized materials and devices for spintronics

    Directory of Open Access Journals (Sweden)

    Koichiro Inomata et al.

    2008-01-01

    and an epitaxial relationship of MgO(001[100]/CoFe2 (001]110]/CFO(001[100] were induced. A SFD consisting of CoFe2 /CFO/Ta on a MgO (001 substrate exhibits the inverse TMR of - 124% at 10 K when the configuration of the magnetizations of CFO and CoFe2 changes from parallel to antiparallel. The inverse TMR suggests the negative spin polarization of CFO, which is consistent with the band structure of CFO obtained by first principle calculation. The - 124% TMR corresponds to the spin filtering efficiency of 77% by the CFO barrier.

  18. Spin-polarization reversal at the interface between benzene and Fe(100)

    KAUST Repository

    Goumri-Said, Souraya

    2013-01-03

    The spin-polarization at the interface between Fe(100) and a benzene is investigated theoretically using density functional theory for two positions of the organic molecule: planar and perpendicular with respect to the substrate. The electronic and magnetic properties as well as the spin-polarization close to the Fermi level strongly depend on the benzene position on the iron surface. An inversion of the spin-polarization is induced by p-d hybridization and charge transfer from the iron to the carbon sites in both configurations.

  19. Nuclear reactivity indices in the context of spin polarized density functional theory

    International Nuclear Information System (INIS)

    Cardenas, Carlos; Lamsabhi, Al Mokhtar; Fuentealba, Patricio

    2006-01-01

    In this work, the nuclear reactivity indices of density functional theory have been generalized to the spin polarized case and their relationship to electron spin polarized indices has been established. In particular, the spin polarized version of the nuclear Fukui function has been proposed and a finite difference approximation has been used to evaluate it. Applications to a series of triatomic molecules demonstrate the ability of the new functions to predict the geometrical changes due to a change in the spin multiplicity. The main equations in the different ensembles have also been presented

  20. Spin Polarization Inversion at Benzene-Absorbed Fe4N Surface

    KAUST Repository

    Zhang, Qian

    2015-05-27

    We report a first-principle study on electronic structure and simulation of the spin-polarized scanning tunneling microscopy graphic of a benzene/Fe4N interface. Fe4N is a compound ferromagnet suitable for many spintronic applications. We found that, depending on the particular termination schemes and interface configurations, the spin polarization on the benzene surface shows a rich variety of properties ranging from cosine-type oscillation to polarization inversion. Spin-polarization inversion above benzene is resulting from the hybridizations between C pz and the out-of-plane d orbitals of Fe atom.

  1. Micromagnetic investigation of the dynamics of magnetization switching induced by a spin polarized current

    Science.gov (United States)

    Lee, Kyung-Jin; Dieny, Bernard

    2006-03-01

    Using micromagnetic modeling, we tested a prediction of single-domain spin-torque theory which switching current density depends only weakly on magnetic cell size. The switching time and current density are strongly affected by the cell size for low spin polarization. Larger samples with a small length-to-width ratio and small spin polarization can exhibit a nonmonotonous dependence of switching time on current. Excitation of incoherent spin waves caused by the circular Oersted field due to the current is responsible for this nonmonotonous dependence. However, the magnetic dynamics recovers a single-domain-like behavior when the spin polarization is high and/or the cell size is small.

  2. Spin-polarized scanning tunneling microscopy: breakthroughs and highlights.

    Science.gov (United States)

    Bode, Matthias

    2012-01-01

    The principle of scanning tunneling microscopy, an imaging method with atomic resolution capability invented by Binnig and Rohrer in 1982, can be adapted for surface magnetism studies by using magnetic probe tips. The contrast mechanism of this so-called spin-polarized scanning tunneling microscopy, or SP-STM, relies on the tunneling magneto-resistance effect, i.e. the tip-sample distance as well as the differential conductance depend on the relative magnetic orientation of tip and sample. To illustrate the working principle and the unique capabilities of SP-STM, this compilation presents some key experiments which have been performed on various magnetic surfaces, such as the topological antiferromagnet Cr(001), a double-layer of Fe which exhibits a stripe- domain pattern with about 50 nm periodicity, and the Mn monolayer on W(110), where the combination of experiment and theory reveal an antiferromagnetic spin cycloid. Recent experimental results also demonstrate the suitability of SP-STM for studies of dynamic properties, such as the spin relaxation time of single magnetic nanostructures.

  3. Spin-polarized semiconductor induced by magnetic impurities in graphene

    Science.gov (United States)

    Daghofer, Maria

    2011-03-01

    Magnetic impurities adsorbed on graphene sheets are coupled antiferromangetically via the itinerant electrons in the graphene. We study this interaction and its impact on the electrons' spectral density by use of unbiased Monte-Carlo simulations. The antiferromagnetic order breaks the symmetry between the sublattices, and a gap for the itinerant electrons opens. Our simulations show that the itinerant states below and above the gap are not dispersionless states trapped by the impurities, but are instead mobile states with a large dispersion. We compare various scenarios for the impurity distribution and find that random doping produces a standard semiconductor. If, on the other hand, all or most of the impurities are localized in the same sublattice, the spin degeneracy is lifted and the conduction band becomes spin-polarized. We also discuss the properties of edge states at edges or magnetic domain boundaries. M.~Daghofer, N.~Zheng, A.~Moreo; Phys.~Rev.~B 82, 121405(R) (2010) Supported by the DFG under the Emmy-Noether Program, and the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. DOE.

  4. Spin polarization and magnetic effects in radical reactions

    International Nuclear Information System (INIS)

    Salikhov, K.M.; Molin, Yu.N.; Sagdeev, R.Z.; Buchachenko, A.L.

    1984-01-01

    Studies on the effects of chemically induced dynamic nuclear and electron polarizations (CIDNP and CIDEP), and magnetic effects in radical reactions, have given rise to a new rapidly-progressing field of chemical physics. It came into being about ten years ago and has been attracting the ever-growing attention of researchers in related areas. The present book is a fairly all-embracing review of the state of affairs in this field. The book presents the physical background (both theoretical and experimental) of CIDNP and CIDEP, of the effects of an external magnetic field and magnetic nuclear moment (magnetic isotope effects) on radical reactions in solutions. Great attention has been paid to the application of chemical spin polarization and magnetic effects to solving various problems of chemical kinetics, structural chemistry, molecular physics, magnetobiology, and radiospectroscopy. The book will be useful for physicists, chemists and biologists employing CIDNP, CIDEP and magnetic effects in their investigations, as well as for researchers in related fields of chemical physics. The book can be also recommended for postgraduates and senior undergraduate students. (Auth.)

  5. Spin-polarized magnetic tunnelling magnetoresistive effects in various junctions

    Science.gov (United States)

    Miyazaki, T.; Tezuka, N.; Kumagai, S.; Ando, Y.; Kubota, H.; Murai, J.; Watabe, T.; Yokota, M.

    1998-03-01

    Recent progress concerning spin-polarized magnetic tunnelling effects for (i) trilayer standard ferromagnet (F)/insulator (I)/ferromagnet (F) junctions, (ii) spin-valve-type junctions, (iii) trilayer or multilayer ferromagnet/granular/ferromagnet junctions and (iv) F/I/F junction with a `wedge-geometry' insulator is reviewed. Special emphasis is placed on the dependence of the tunnel magnetoresistance ratio on temperature and also the intensity of the applied voltage. It was found that the resistance for the saturation magnetization state, 0022-3727/31/6/009/img1, and the tunnelling magnetoresistance ratio, TMR, of an 0022-3727/31/6/009/img2 junction decreased rapidly with increasing temperature, whereas those of a 0022-3727/31/6/009/img3 junction were insensitive to temperature. Concerning the bias voltage dependence of 0022-3727/31/6/009/img1 and TMR, the same tendency with temperature was observed for 0022-3727/31/6/009/img2 and 0022-3727/31/6/009/img3 junctions. Spin-valve-type junction exchange biased by a FeMn layer exhibits a relatively large TMR ratio up to about 400 K.

  6. Fusion with highly spin polarized HD and D2

    International Nuclear Information System (INIS)

    Honig, A.; Letzring, S.; Skupsky, S.

    1993-01-01

    Our experimental efforts over the past 5 years have been aimed at cazrying out ICF shots with spin-polarized 0 fuel. We successfully prepared polarized 0 in HD, and solved the problems of loading target shells with our carefully prepared isotopic -rnixt.l.l?-es, polarizing them so that the 0 polarization remains metastably frozen-in for about half a day, and carrying out the various cold transfer requirements at Syracuse, where the target is prepared, and at Rochester, where the cold target is inserted fusion chamber. Upon shooting the accurately positioned unpolarized high density cold target, no neutron yield was observed. Inspection inside the OMEGA tank after the shot indicated the absence of neutron yield was dus to mal-timing or insufficient retraction rate of OMEGA'S fast shroud mechanism, resulting in interception of at least 20 of the 24 laser beams by the faulty shroud. In spits of this, all alements of the complex experiment we originally undertook have been successfully demonstrated, and the cold retrieval concepts and methods we developed are being utilized on the ICF upgrades at Rochester and at Livermore. In addition to the solution of the interface problems, we obtained novel results on polymer shell characteristics at low temperatures, and continuation of these experiments is c = ently supported by KLUP. Extensive additional mappings were ca=ied out of nuclear spin relaxation rates of H and D in solid HD in the temperature-magnetic field rangs of 0.01 to 4.2K and 0 - 13 Tesla. New phenomena were discovered, such as association of impurity clustering with very low temperature motion, and inequality of the growth-rate and decay-rate of the magnetization

  7. Fusion with highly spin polarized HD and D2

    International Nuclear Information System (INIS)

    Honig, A.; Letzring, S.; Skupsky, S.

    1993-01-01

    The experimental efforts over the past 5 years have been aimed at carrying out ICF shots with spin-polarized D fuel. The authors successfully prepared polarized D in HD, and solved the problems of loading target shells with their carefully prepared isotopic mixtures, polarizing them so that the D polarization remains metastably frozen-in for about half a day, and carrying out the various cold transfer requirements at Syracuse, where the target is prepared, and at Rochester, where the cold target is inserted into the OMEGA fusion chamber. A principal concern during this past year was overcoming difficulties encountered in maintaining the integrity of the fragile cold target during the multitude of cold-transfers required for the experiment. These difficulties arose from insufficient rigidity of the cold transfer systems, which were constrained to be of small diameter by the narrow central access bore of the dilution refrigerator, and were exacerbated by the multitude of required target shell manipulations between different environments, each with different coupling geometry, including target shell permeation, polarization, storage, transport, retrieval and insertion into OMEGA. The authors did solve all of these problems, and were able to position a cold, high density but unpolarized target with required precision in OMEGA. Upon shooting the accurately positioned unpolarized high density cold target, no neutron yield was observed. Inspection inside the OMEGA tank after the shot indicated the absence of neutron yield was due to mal-timing or insufficient retraction rate of OMEGA's fast shroud mechanism, resulting in interception of at least 20 of the 24 laser beams by the faulty shroud. In spite of this, all elements of the complex experiment the authors originally undertook have been successfully demonstrated, and the cold retrieval concepts and methods they developed are being utilized on the ICF upgrades at Rochester and at Livermore

  8. Spin polarization, orbital occupation and band gap opening in vanadium dioxide: The effect of screened Hartree-Fock exchange

    KAUST Repository

    Wang, Hao

    2014-07-01

    The metal-insulator transition of VO2 so far has evaded an accurate description by density functional theory. The screened hybrid functional of Heyd, Scuseria and Ernzerhof leads to reasonable solutions for both the low-temperature monoclinic and high-temperature rutile phases only if spin polarization is excluded from the calculations. We explore whether a satisfactory agreement with experiment can be achieved by tuning the fraction of Hartree Fock exchange (α) in the density functional. It is found that two branches of locally stable solutions exist for the rutile phase for 12.5%≤α≤20%. One is metallic and has the correct stability as compared to the monoclinic phase, the other is insulating with lower energy than the metallic branch. We discuss these observations based on the V 3d orbital occupations and conclude that α=10% is the best possible choice for spin-polarized VO2 calculations. © 2014 Elsevier B.V. All rights reserved.

  9. From epitaxial growth of ferrite thin films to spin-polarized tunnelling

    International Nuclear Information System (INIS)

    Moussy, Jean-Baptiste

    2013-01-01

    This paper presents a review of the research which is focused on ferrite thin films for spintronics. First, I will describe the potential of ferrite layers for the generation of spin-polarized currents. In the second step, the structural and chemical properties of epitaxial thin films and ferrite-based tunnel junctions will be presented. Particular attention will be given to ferrite systems grown by oxygen-assisted molecular beam epitaxy. The analysis of the structure and chemistry close to the interfaces, a key-point for understanding the spin-polarized tunnelling measurements, will be detailed. In the third part, the magnetic and magneto-transport properties of magnetite (Fe 3 O 4 ) thin films as a function of structural defects such as the antiphase boundaries will be explained. The spin-polarization measurements (spin-resolved photoemission, tunnel magnetoresistance) on this oxide predicted to be half-metallic will be discussed. Fourth, the potential of magnetic tunnel barriers, such as CoFe 2 O 4 , NiFe 2 O 4 or MnFe 2 O 4 , whose insulating behaviour and the high Curie temperatures make it exciting candidates for spin filtering at room temperature will be described. Spin-polarized tunnelling experiments, involving either Meservey–Tedrow or tunnel magnetoresistance measurements, will reveal significant spin-polarizations of the tunnelling current at low temperatures but also at room temperatures. Finally, I will mention a few perspectives with ferrite-based heterostructures. (topical review)

  10. Injection and detection of a spin-polarized current in a light-emitting diode

    Science.gov (United States)

    Fiederling, R.; Keim, M.; Reuscher, G.; Ossau, W.; Schmidt, G.; Waag, A.; Molenkamp, L. W.

    1999-12-01

    The field of magnetoelectronics has been growing in practical importance in recent years. For example, devices that harness electronic spin-such as giant-magnetoresistive sensors and magnetoresistive memory cells-are now appearing on the market. In contrast, magnetoelectronic devices based on spin-polarized transport in semiconductors are at a much earlier stage of development, largely because of the lack of an efficient means of injecting spin-polarized charge. Much work has focused on the use of ferromagnetic metallic contacts, but it has proved exceedingly difficult to demonstrate polarized spin injection. More recently, two groups have reported successful spin injection from an NiFe contact, but the observed effects of the spin-polarized transport were quite small (resistance changes of less than 1%). Here we describe a different approach, in which the magnetic semiconductor BexMnyZn1-x-ySe is used as a spin aligner. We achieve injection efficiencies of 90% spin-polarized current into a non-magnetic semiconductor device. The device used in this case is a GaAs/AlGaAs light-emitting diode, and spin polarization is confirmed by the circular polarization state of the emitted light.

  11. Spin polarization of tunneling current in barriers with spin-orbit coupling.

    Science.gov (United States)

    Fujita, T; Jalil, M B A; Tan, S G

    2008-03-19

    We present a general method for evaluating the maximum transmitted spin polarization and optimal spin axis for an arbitrary spin-orbit coupling (SOC) barrier system, in which the spins lie in the azimuthal plane and finite spin polarization is achieved by wavevector filtering of electrons. Besides momentum filtering, another prerequisite for finite spin polarization is asymmetric occupation or transmission probabilities of the eigenstates of the SOC Hamiltonian. This is achieved most efficiently by resonant tunneling through multiple SOC barriers. We apply our analysis to common SOC mechanisms in semiconductors: pure bulk Dresselhaus SOC, heterostructures with mixed Dresselhaus and Rashba SOC and strain-induced SOC. In particular, we find that the interplay between Dresselhaus and Rashba SOC effects can yield several advantageous features for spin filter and spin injector functions, such as increased robustness to wavevector spread of electrons.

  12. In situ scanning tunneling microscope tip treatment device for spin polarization imaging

    Science.gov (United States)

    Li, An-Ping [Oak Ridge, TN; Jianxing, Ma [Oak Ridge, TN; Shen, Jian [Knoxville, TN

    2008-04-22

    A tip treatment device for use in an ultrahigh vacuum in situ scanning tunneling microscope (STM). The device provides spin polarization functionality to new or existing variable temperature STM systems. The tip treatment device readily converts a conventional STM to a spin-polarized tip, and thereby converts a standard STM system into a spin-polarized STM system. The tip treatment device also has functions of tip cleaning and tip flashing a STM tip to high temperature (>2000.degree. C.) in an extremely localized fashion. Tip coating functions can also be carried out, providing the tip sharp end with monolayers of coating materials including magnetic films. The device is also fully compatible with ultrahigh vacuum sample transfer setups.

  13. Spin polarized tunnelling investigation of nanometre Co clusters by means of a Ni bulk tip

    International Nuclear Information System (INIS)

    Rastei, M V; Bucher, J P

    2006-01-01

    A massive Ni tip is used in spin polarized scanning tunnelling microscopy (SP STM) to explore the magnetization state of nanometre Co clusters, self-organized on the Au(111) surface. Constant current STM images taken at 4.6 K show a bimodal distribution of the cluster heights, accounting for the spin polarization of the STM junction. The spin polarization of the tunnel junction as a function of the bias voltage is found to depend on the local density of states of the sample examined. Changing the vacuum barrier parameters by bringing the tip closer to the surface leads to a reduction in the tunnelling magnetoresistance that may be attributed to spin flip effects. (letter to the editor)

  14. Spin polarization of tunneling current in barriers with spin-orbit coupling

    International Nuclear Information System (INIS)

    Fujita, T; Jalil, M B A; Tan, S G

    2008-01-01

    We present a general method for evaluating the maximum transmitted spin polarization and optimal spin axis for an arbitrary spin-orbit coupling (SOC) barrier system, in which the spins lie in the azimuthal plane and finite spin polarization is achieved by wavevector filtering of electrons. Besides momentum filtering, another prerequisite for finite spin polarization is asymmetric occupation or transmission probabilities of the eigenstates of the SOC Hamiltonian. This is achieved most efficiently by resonant tunneling through multiple SOC barriers. We apply our analysis to common SOC mechanisms in semiconductors: pure bulk Dresselhaus SOC, heterostructures with mixed Dresselhaus and Rashba SOC and strain-induced SOC. In particular, we find that the interplay between Dresselhaus and Rashba SOC effects can yield several advantageous features for spin filter and spin injector functions, such as increased robustness to wavevector spread of electrons

  15. Nuclear spin polarized H and D by means of spin-exchange optical pumping

    Science.gov (United States)

    Stenger, Jörn; Grosshauser, Carsten; Kilian, Wolfgang; Nagengast, Wolfgang; Ranzenberger, Bernd; Rith, Klaus; Schmidt, Frank

    1998-01-01

    Optically pumped spin-exchange sources for polarized hydrogen and deuterium atoms have been demonstrated to yield high atomic flow and high electron spin polarization. For maximum nuclear polarization the source has to be operated in spin temperature equilibrium, which has already been demonstrated for hydrogen. In spin temperature equilibrium the nuclear spin polarization PI equals the electron spin polarization PS for hydrogen and is even larger than PS for deuterium. We discuss the general properties of spin temperature equilibrium for a sample of deuterium atoms. One result are the equations PI=4PS/(3+PS2) and Pzz=PSṡPI, where Pzz is the nuclear tensor polarization. Furthermore we demonstrate that the deuterium atoms from our source are in spin temperature equilibrium within the experimental accuracy.

  16. Defect-enhanced Rashba spin-polarized currents in carbon nanotubes

    Science.gov (United States)

    Santos, Hernán; Chico, Leonor; Alvarellos, J. E.; Latgé, A.

    2017-10-01

    The production of spin-polarized currents in pristine carbon nanotubes with Rashba spin-orbit interactions has been shown to be very sensitive to the symmetry of the tubes and the geometry of the setup. Here we analyze the role of defects on the spin quantum conductances of metallic carbon nanotubes due to an external electric field. We show that localized defects, such as adsorbed hydrogen atoms or pentagon-heptagon pairs, increase the Rashba spin-polarized current. Moreover, this enhancement takes place for energies closer to the Fermi energy as compared to the response of pristine tubes. Such increments can be even larger when several equally spaced defects are introduced into the system. We explore different arrangements of defects, showing that for certain geometries there are flips of the spin-polarized current and even transport suppression. Our results indicate that spin valve devices at the nanoscale may be achieved via defect engineering in carbon nanotubes.

  17. Spin polarization versus color–flavor locking in high-density quark matter

    DEFF Research Database (Denmark)

    Tsue, Yasuhiko; da Providência, João; Providência, Constança

    2015-01-01

    It is shown that spin polarization with respect to each flavor in three-flavor quark matter occurs instead of color–flavor locking at high baryon density by using the Nambu–Jona-Lasinio model with four-point tensor-type interaction. Also, it is indicated that the order of phase transition between...... the color–flavor-locked phase and the spin-polarized phase is the first order by means of second-order perturbation theory.......It is shown that spin polarization with respect to each flavor in three-flavor quark matter occurs instead of color–flavor locking at high baryon density by using the Nambu–Jona-Lasinio model with four-point tensor-type interaction. Also, it is indicated that the order of phase transition between...

  18. Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States.

    Science.gov (United States)

    Bentmann, H; Maaß, H; Krasovskii, E E; Peixoto, T R F; Seibel, C; Leandersson, M; Balasubramanian, T; Reinert, F

    2017-09-08

    A comprehensive understanding of spin-polarized photoemission is crucial for accessing the electronic structure of spin-orbit coupled materials. Yet, the impact of the final state in the photoemission process on the photoelectron spin has been difficult to assess in these systems. We present experiments for the spin-orbit split states in a Bi-Ag surface alloy showing that the alteration of the final state with energy may cause a complete reversal of the photoelectron spin polarization. We explain the effect on the basis of ab initio one-step photoemission theory and describe how it originates from linear dichroism in the angular distribution of photoelectrons. Our analysis shows that the modulated photoelectron spin polarization reflects the intrinsic spin density of the surface state being sampled differently depending on the final state, and it indicates linear dichroism as a natural probe of spin-orbit coupling at surfaces.

  19. Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor

    Science.gov (United States)

    Choi, Seokhwan; Choi, Hyoung Joon; Ok, Jong Mok; Lee, Yeonghoon; Jang, Won-Jun; Lee, Alex Taekyung; Kuk, Young; Lee, SungBin; Heinrich, Andreas J.; Cheong, Sang-Wook; Bang, Yunkyu; Johnston, Steven; Kim, Jun Sung; Lee, Jhinhwan

    2017-12-01

    We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr2VO3FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C4 (2 ×2 ) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C4 (2 ×2 ) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C4 state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors.

  20. Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor.

    Science.gov (United States)

    Choi, Seokhwan; Choi, Hyoung Joon; Ok, Jong Mok; Lee, Yeonghoon; Jang, Won-Jun; Lee, Alex Taekyung; Kuk, Young; Lee, SungBin; Heinrich, Andreas J; Cheong, Sang-Wook; Bang, Yunkyu; Johnston, Steven; Kim, Jun Sung; Lee, Jhinhwan

    2017-12-01

    We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr_{2}VO_{3}FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C_{4} (2×2) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C_{4} (2×2) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C_{4} state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors.

  1. Hardness and softness reactivity kernels within the spin-polarized density-functional theory

    International Nuclear Information System (INIS)

    Chamorro, Eduardo; De Proft, Frank; Geerlings, Paul

    2005-01-01

    Generalized hardness and softness reactivity kernels are defined within a spin-polarized density-functional theory (SP-DFT) conceptual framework. These quantities constitute the basis for the global, local (i.e., r-position dependent), and nonlocal (i.e., r and r ' -position dependents) indices devoted to the treatment of both charge-transfer and spin-polarization processes in such a reactivity framework. The exact relationships between these descriptors within a SP-DFT framework are derived and the implications for chemical reactivity in such context are outlined

  2. Spontaneous spin-polarization and phase transition in the relativistic approach

    International Nuclear Information System (INIS)

    Maruyama, Tomoyuki; Tatsumi, Toshitaka

    2001-01-01

    We study the spin-polarization mechanism in the highly dense nuclear matter with the relativistic mean-field approach. In the relativistic Hartree-Fock framework we find that there are two kinds of spin-spin interaction channels, which are the axial-vector and tensor exchange ones. If each interaction is strong and different sign, the system loses the spherical symmetry and holds the spin-polarization in the high-density region. When the axial-vector interaction is negative enough, the system holds ferromagnetism. (author)

  3. Interplay between magnetism and conductivity derived from spin-polarized donor radicals.

    Science.gov (United States)

    Sugawara, Tadashi; Komatsu, Hideji; Suzuki, Kentaro

    2011-06-01

    Tutorial review: to achieve molecule-based spintronic devices, an organic conducting magnet that exhibits both conductivity and magnetism in a cooperative manner must be constructed. As a building block for such new materials, a spin-polarized donor radical, which serves as a molecular "spin-filter" in its singly oxidized state, was designed and synthesized. The resistivity of ion radical salts of selenium-substituted, tetrathiafulvalene-based spin-polarized donor radicals decreased substantially in the presence of a magnetic field, thus indicating cooperative conductivity and magnetism.

  4. Electronic Structures of Magnetic Iron and Cobalt Thin Films on TUNGSTEN(001): a Spin-Polarized Inverse Photoemission Study

    Science.gov (United States)

    Cai, Qing

    Electronic structure is a central question in metallic magnetism as well as in magnetic materials research. The electronic properties in a two-dimensional system such as thin films of a few atomic layers is an important issue in surface science. The epitaxial thin film preparation and morphology are of special technological interests. In this thesis, these questions are addressed. Spin-polarized inverse photoemission spectroscopy is used to study the unoccupied electron band states in magnetic thin film magnets of Fe and Co epitaxially grown on W(001) surface. The clean W(001) surface was studied by angle -resolved inverse photoemission spectroscopy and the bulk band dispersion was determined. Ultrathin Fe overlayers on W(001) show a square lateral crystal structure similar to the bcc-Fe(001) surface. The electronic structure develops into a structure that is close to that of bulk Fe at about four atomic layers. In the normal-incidence spin polarized inverse photoemission spectra, direct transitions to the majority and minority final states near the H^'_ {25} point are identified in good agreement with the theoretical calculations. One Fe monolayer, or multilayers less than four, showed behavior corresponding to a gradually reduced Curie temperature. When the film thickness is reduced, the spin-resolved spectral behavior show that the majority spin signal peak moves from near the Fermi energy to about 1.3 eV while the minority peak stays at about the same position near 1.3 eV. The results are used to examine the spatial correlation of the spin fluctuations in the system in comparison with a theoretical spectral calculation, and favors the disordered-local-moment picture in the contemporary theory of itinerant magnetism. The Co overlayer shows an overlayer structure that consists of equivalent, mutually rotated domains of distorted hexagonal lateral structure. For one atomic layer of Co in that structure, which has a nominal lateral atomic density twice that of the

  5. Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

    DEFF Research Database (Denmark)

    Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.

    2003-01-01

    Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified...

  6. Towards 100% spin-polarized charge-injection : The half-metallic NiMnSb/CdS interface

    NARCIS (Netherlands)

    de Wijs, G.A.; de Groot, R A

    2001-01-01

    Spin-electronics requires an electron source with a spin-polarization as high as possible. For this, half-metallic materials seem ideally suited as they exhibit 100% spin polarization. Because of its high Curie temperature and compatibility with existing semiconductor technology, NiMnSb is a most

  7. Laser detection of spin-polarized hydrogen from HCl and HBr photodissociation: comparison of H- and halogen-atom polarizations.

    Science.gov (United States)

    Sofikitis, Dimitris; Rubio-Lago, Luis; Bougas, Lykourgos; Alexander, Andrew J; Rakitzis, T Peter

    2008-10-14

    Thermal HCl and HBr molecules were photodissociated using circularly polarized 193 nm light, and the speed-dependent spin polarization of the H-atom photofragments was measured using polarized fluorescence at 121.6 nm. Both polarization components, described by the a(0)(1)(perpendicular) and Re[a(1)(1)(parallel, perpendicular)] parameters which arise from incoherent and coherent dissociation mechanisms, are measured. The values of the a(0)(1)(perpendicular) parameter, for both HCl and HBr photodissociation, are within experimental error of the predictions of both ab initio calculations and of previous measurements of the polarization of the halide cofragments. The experimental and ab initio theoretical values of the Re[a(1)(1)(parallel, perpendicular)] parameter show some disagreement, suggesting that further theoretical investigations are required. Overall, good agreement occurs despite the fact that the current experiments photodissociate molecules at 295 K, whereas previous measurements were conducted at rotational temperatures of about 15 K.

  8. Spin polarized auger electron spectroscopy (SPAES): An element specific local magnetization probe of magnetic materials

    Science.gov (United States)

    Anilturk, Onder S.

    Spin Polarized Auger Electron Spectroscopy (SPAES) is found to have application for investigating fundamental properties as well as element specific local magnetization information on magnetic materials. By using the uniqueness of the UTA-SEMPA tool, one can obtain the surface magnetic domain microstructure and also perform SPAES studies by probing a single domain at the surface. In the current study, knowing the probed domain, spin polarization of electrons from super Coster-Kronig MVV Auger emissions on 3%Si-Fe sheets have been investigated. It is observed that on both sides of 180° domains, separated by a domain wall with an out-of-plane component of magnetization, the spin polarized Auger spectra exhibit similar distributions with high polarization structures, which are consistent with the published data. The element specificity of the system is applied to Gd-Co composite system. Details of 4d core hole initiated Auger transitions showed that the 5d states have enhanced spin polarization, confirming the coupling of moments in the composite system via 5d states of Gd. It is also unambiguously observed that Co magnetic moments are indeed aligned antiparallel to the Gd ones via 4f-5d positive exchange and 3d-5d hybridization.

  9. Probing spin-polarized tunneling at high bias and temperature with a magnetic tunnel transistor

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Min, B.C.; Sanderink, Johannes G.M.; Lodder, J.C.; Jansen, R.

    2005-01-01

    The magnetic tunnel transistor (MTT) is a three terminal hybrid device that consists of a tunnel emitter, a ferromagnetic (FM) base, and a semiconductor collector. In the MTT with a FM emitter and a single FM base, spin-polarized hot electrons are injected into the base by tunneling. After

  10. Tunneling Spectroscopy Study of Spin-Polarized Quasiparticle Injection Effects in Cuparate/Manganite Heterostructures

    Science.gov (United States)

    Wei, J. Y. T.; Yeh, N. C.; Vasquez, R. P.

    1998-01-01

    Scanning tunneling spectroscopy was performed at 4.2K on epitaxial thin-film heterostructures comprising YBa2Cu3O7 and La0.7Ca0.3MnO3, to study the microscopic effects of spin-polarized quasiparticle injection from the half-metallic ferromagnetic manganite on the high-Tc cuprate superconductor.

  11. Spin polarization in top pair production in association with two photons at NLO+PS

    CERN Document Server

    Luisoni, Gionata

    2017-01-01

    This talk focuses on the impact of top-quark spin polarization effects in Higgs boson production in association with a top-quark pair, where the Higgs boson decays to two photons. Predictions for the signal are compared with direct top-quark pair production in association with two photons at NLO+PS.

  12. Spin-polarized versus chiral condensate in quark matter at finite temperature and density

    DEFF Research Database (Denmark)

    Matsuoka, Hiroaki; Tsue, Yasuhiko; da Providencia, Joao

    2016-01-01

    It is shown that the spin-polarized condensate appears in quark matter at high baryon density and low temperature due to the tensor-type four-point interaction in the Nambu-Jona-Lasiniotype model as a low-energy effective theory of quantum chromodynamics. It is indicated within this low...

  13. Tunnel spin polarization versus energy for clean and doped Al2O3 barriers

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Lodder, J.C.; Jansen, R.

    2007-01-01

    The variation of the tunnel spin-polarization (TSP) with energy is determined using a magnetic tunnel transistor, allowing quantification of the energy dependent TSP separately for both ferromagnet/insulator interfaces and direct correlation with the tunnel magnetoresistance (TMR) measured in the

  14. Tunnel Spin Polarization Versus Energy for Clean and Doped Al2O3 Barriers

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Lodder, J.C.; Jansen, R.

    2007-01-01

    The variation of the tunnel spin-polarization (TSP) with energy is determined using a magnetic tunnel transistor, allowing quantification of the energy dependent TSP separately for both ferromagnet/insulator interfaces and direct correlation with the tunnel magnetoresistance (TMR) measured in the

  15. Spin-polarized transport in a two-dimensional electron gas with interdigital-ferromagnetic contacts

    DEFF Research Database (Denmark)

    Hu, C.-M.; Nitta, Junsaku; Jensen, Ane

    2001-01-01

    Ferromagnetic contacts on a high-mobility, two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin-orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect specific spi...

  16. Spin-filter scanning tunneling microscopy : a novel technique for the analysis of spin polarization on magnetic surfaces and spintronic devices

    NARCIS (Netherlands)

    Vera Marun, I.J.

    2010-01-01

    This thesis deals with the development of a versatile technique to measure spin polarization with atomic resolution. A microscopy technique that can measure electronic spin polarization is relevant for characterization of magnetic nanostructures and spintronic devices. Scanning tunneling microscopy

  17. Analytical polarization calculations beyond SLIM

    International Nuclear Information System (INIS)

    Barber, D.P.

    1989-01-01

    A comparison is made between the theories of Bell and Leinaas and of Derbenev and Kondratenko for the spin polarization in electron storage rings. A calculation of polarization in HERA using the program SMILE of Mane is presented

  18. EDITORIAL: New materials with high spin polarization: half-metallic Heusler compounds

    Science.gov (United States)

    Felser, Claudia; Hillebrands, Burkard

    2007-03-01

    thin film Appl. Phys. Lett. 88 262503 [6] Thomas A, Meyners D, Ebke D, Liu N-N, Sacher M D, Schmalhorst J, Reiss G, Ebert H, and Hütten A 2006 Inverted spin polarization of Heusler alloys for spintronic devices Appl. Phys. Lett. 89 012502 [7] Hillebrands B and Felser C 2006 Editorial: High-spin polarization of Heusler alloys J. Phys. D: Appl. Phys. 39 issue 5 http://stacks.iop.org/0022-3727/39/i=5 [8] Galanakis I, Mavropoulos Ph and Dederichs P H 2006 Electronic structure and Slater-Pauling behaviour in half-metallic Heusler alloys calculated from first principles J. Phys. D: Appl. Phys. 39 765 J. Phys. D: Appl. Phys. 39 765 [9] Kandpal H C, Felser C and Seshadri R 2006 Covalent bonding and the nature of band gaps in some half-Heusler compounds J. Phys. D: Appl. Phys. 39 776 [10] Kallmayer M, Elmers H J, Balke B, Wurmehl S, Emmerling F, Fecher G H and Felser C 2006 Magnetic properties of Co2Mn1-xFexSi Heusler alloys J. Phys. D: Appl. Phys. 39 786 [11] Attema J J, de Wijs G A and de Groot R A 2006 The continuing drama of the half-metal/semiconductor interface J. Phys. D: Appl. Phys. 39 793 [12] Leziac M, Mavropoulos Ph, Bihlmayer G and Blügel S 2006 Scanning tunnelling microscopy of surfaces of half-metals: an ab-initio study on NiMnSb(001) J. Phys. D: Appl. Phys. 39 797 [13] Wurmehl S, Fecher G H, Kroth K, Kronast F, Dürr H A, Takeda Y, Saitoh Y, Kobayashi K, Lin H-J, Schönhense G and Felser C 2006 Electronic structure and spectroscopy of the quaternary Heusler alloy Co2Cr1-xFexAl J. Phys. D: Appl. Phys. 39 803 [14] Inomata K, Okamura S, Miyazaki A, Kikuchi M, Tezuka N, Wojcik M and Jedryka E 2006 Structural and magnetic properties and tunnel magnetoresistance for Co2(Cr,Fe)Al and Co2FeSi full-Heusler alloys J. Phys. D: Appl. Phys. 39 816 [15] Yamamoto M, Marukame T, Ishikawa T, Matsuda K, Uemura T and Arita M 2006 Fabrication of fully epitaxial magnetic tunnel junctions using cobalt-based full-Heusler alloy thin film and their tunnel magnetoresistance

  19. Spin-polarized deuterium : stabilization in magnetic traps

    NARCIS (Netherlands)

    Koelman, J.M.V.A.; Stoof, H.T.C.; Verhaar, B.J.; Walraven, J.T.M.

    1987-01-01

    We report on a calculation of the spin-exchange two-body rate constants associated with the population dynamics of the hyperfine levels of atomic deuterium as a function of magnetic field in the Boltzmann zero temperature limit. We find that a gas of low field seeking deuterium atoms trapped in a

  20. Anomalous Hall effect and current spin polarization in Co2Fe X Heusler compounds (X =Al , Ga , In , Si , Ge , and Sn ): A systematic ab initio study

    Science.gov (United States)

    Huang, Hung-Lung; Tung, Jen-Chuan; Guo, Guang-Yu

    2015-04-01

    Co-based Heusler compounds are ferromagnetic with a high Curie temperature and a large magnetization density, and thus are promising for spintronic applications. In this paper, we perform a systematic ab initio study of two principal spin-related phenomena, namely, anomalous Hall effect and current spin polarization, in Co2-based Heusler compounds Co2Fe X (X =Al , Ga , In , Si , Ge , Sn ) in the cubic L2 1 structure within the density functional theory with the generalized gradient approximation (GGA). The accurate all-electron full-potential linearized augmented plane-wave method is used. First, we find that the spin polarization of the longitudinal current (PL) in Co2Fe X (X =Al , Ga , In , Al0.5Si0.5 , and Sn ) is ˜100 % even though that of the electronic states at the Fermi level (PD) is not. Further, the other compounds also have a high current spin polarization with PL>85 %. This indicates that all the Co2Fe X compounds considered are promising for spin-transport devices. Interestingly, PD is negative in Co2Fe X (X =Si , Ge , and Sn ), differing in sign from the PL as well as that from the transport experiments. Second, the calculated anomalous Hall conductivities (AHCs) are moderate, being within 200 S/cm, and agree well with the available experiments on a highly L2 1 ordered Co2FeSi specimen although they differ significantly from the reported experiments on other compounds where the B2 antisite disorders were present. Surprisingly, the AHC in Co2FeSi decreases and then changes sign when Si is replaced by Ge and finally by Sn. Third, the calculated total magnetic moments agree well with the corresponding experimental ones in all the studied compounds except Co2FeSi where a difference of 0.3 μB/f .u . exists. We also perform the GGA plus on-site Coulomb interaction U calculations in the GGA + U scheme. We find that including the U affects the calculated total magnetic moment, spin polarization and AHC significantly, and in most cases, unfortunately

  1. Effect of spin polarization on the structural properties and bond ...

    Indian Academy of Sciences (India)

    The population of Fe–B bond increases from 0.175 (FM) to 0.2 (NM) in FeB. On the other hand, the calculated bond overlap populations in Fe2B kept unchanged and the value is 0.15 electrons in the two cases. 3.3 Bond hardness. Hardness is a measure of the resistance of materials against permanent deformations.

  2. Spin-polarized spin-orbit-split quantum-well states in a metal film

    Energy Technology Data Exchange (ETDEWEB)

    Varykhalov, Andrei; Sanchez-Barriga, Jaime; Gudat, Wolfgang; Eberhardt, Wolfgang; Rader, Oliver [BESSY Berlin (Germany); Shikin, Alexander M. [St. Petersburg State University (Russian Federation)

    2008-07-01

    Elements with high atomic number Z lead to a large spin-orbit coupling. Such materials can be used to create spin-polarized electronic states without the presence of a ferromagnet or an external magnetic field if the solid exhibits an inversion asymmetry. We create large spin-orbit splittings using a tungsten crystal as substrate and break the structural inversion symmetry through deposition of a gold quantum film. Using spin- and angle-resolved photoelectron spectroscopy, it is demonstrated that quantum-well states forming in the gold film are spin-orbit split and spin polarized up to a thickness of at least 10 atomic layers. This is a considerable progress as compared to the current literature which reports spin-orbit split states at metal surfaces which are either pure or covered by at most a monoatomic layer of adsorbates.

  3. Spin-polarized free electron beam interaction with radiation and superradiant spin-flip radiative emission

    Directory of Open Access Journals (Sweden)

    A. Gover

    2006-06-01

    Full Text Available The problems of spin-polarized free-electron beam interaction with electromagnetic wave at electron-spin resonance conditions in a magnetic field and of superradiant spin-flip radiative emission are analyzed in the framework of a comprehensive classical model. The spontaneous emission of spin-flip radiation from electron beams is very weak. We show that the detectivity of electron spin resonant spin-flip and combined spin-flip/cyclotron-resonance-emission radiation can be substantially enhanced by operating with ultrashort spin-polarized electron beam bunches under conditions of superradiant (coherent emission. The proposed radiative spin-state modulation and the spin-flip radiative emission schemes can be used for control and noninvasive diagnostics of polarized electron/positron beams. Such schemes are of relevance in important scattering experiments off nucleons in nuclear physics and off magnetic targets in condensed matter physics.

  4. Control of the spin polarization of photoelectrons/photoions using short laser pulses

    International Nuclear Information System (INIS)

    Nakajima, Takashi

    2004-01-01

    We present a generic pump-probe scheme to control spin polarization of photoelectrons/photoions by short laser pulses. By coherently exciting fine structure manifolds of a multi-valence-electron system by the pump laser, a superposition of fine structure states is created. Since each fine structure state can be further decomposed into a superposition of various spin states of valence electrons, each spin component evolves differently in time. This means that varying the time delay between the pump and probe lasers leads to the control of spin states. Specific theoretical results are presented for two-valence-electron atoms, in particular for Mg, which demonstrate that not only the degree of spin polarization but also its sign can be manipulated through time delay. Since the underline physics is rather general and transparent, the presented idea may be potentially applied to nanostructures such as quantum wells and quantum dots

  5. Intense source of spin-polarized electrons using laser-induced optical pumping

    International Nuclear Information System (INIS)

    Gray, L.G.; Giberson, K.W.; Cheng, C.; Keiffer, R.S.; Dunning, F.B.; Walters, G.K.

    1983-01-01

    A source of spin-polarized electrons based on a laser-pumped flowing helium afterglow is described. He(2 3 S) atoms contained in the afterglow are optically pumped using circularly polarized 1.08-μm (2 3 S→2 3 P) radiation provided by a NaF (F 2+ )( color-center laser. Spin angular momentum conservation in subsequent chemi-ionization reactions with CO 2 produces polarized electrons that are extracted from the afterglow. At low currents, < or approx. =1 μA, polarizations of approx.70%--80% are achieved. At higher currents the polarization decreases, falling to approx.40% at 50 μA. The spin polarization can be simply reversed (P→-P) and the source is suitable for use in the majority of low-energy spin-dependent scattering experiments proposed to date

  6. Coupled spin and charge collective excitations in a spin polarized electron gas

    International Nuclear Information System (INIS)

    Marinescu, D.C.; Quinn, J.J.; Yi, K.S.

    1997-01-01

    The charge and longitudinal spin responses induced in a spin polarized quantum well by a weak electromagnetic field are investigated within the framework of the linear response theory. The authors evaluate the excitation frequencies for the intra- and inter-subband transitions of the collective charge and longitudinal spin density oscillations including many-body corrections beyond the random phase approximation through the spin dependent local field factors, G σ ± (q,ω). An equation-of-motion method was used to obtain these corrections in the limit of long wavelengths, and the results are given in terms of the equilibrium pair correlation function. The finite degree of spin polarization is shown to introduce coupling between the charge and spin density modes, in contrast with the result for an unpolarized system

  7. Two-photon spin-polarization spectroscopy in silicon-doped GaAs.

    Science.gov (United States)

    Miah, M Idrish

    2009-05-14

    We generate spin-polarized electrons in bulk GaAs using circularly polarized two-photon pumping with excess photon energy (DeltaE) and detect them by probing the spin-dependent transmission of the sample. The spin polarization of conduction band electrons is measured and is found to be strongly dependent on DeltaE. The initial polarization, pumped with DeltaE=100 meV, at liquid helium temperature is estimated to be approximately 49.5%, which is very close to the theoretical value (50%) permitted by the optical selection rules governing transitions from heavy-hole and light-hole states to conduction band states in a bulk sample. However, the polarization pumped with larger DeltaE decreases rapidly because of the exciting carriers from the split-off band.

  8. Spin-wave propagation and spin-polarized electron transport in single-crystal iron films

    Science.gov (United States)

    Gladii, O.; Halley, D.; Henry, Y.; Bailleul, M.

    2017-11-01

    The techniques of propagating spin-wave spectroscopy and current-induced spin-wave Doppler shift are applied to a 20-nm-thick Fe/MgO(001) film. The magnetic parameters extracted from the position of the spin-wave resonance peaks are very close to those tabulated for bulk iron. From the zero-current propagating wave forms, a group velocity of 4 km/s and an attenuation length of about 6 μ m are extracted for 1.6-μ m -wavelength spin wave at 18 GHz. From the measured current-induced spin-wave Doppler shift, we extract a surprisingly high degree of spin polarization of the current of 83 % , which constitutes the main finding of this work. This set of results makes single-crystalline iron a promising candidate for building devices utilizing high-frequency spin waves and spin-polarized currents.

  9. Illuminating "spin-polarized" Bloch wave-function projection from degenerate bands in decomposable centrosymmetric lattices

    Science.gov (United States)

    Li, Pengke; Appelbaum, Ian

    2018-03-01

    The combination of space inversion and time-reversal symmetries results in doubly degenerate Bloch states with opposite spin. Many lattices with these symmetries can be constructed by combining a noncentrosymmetric potential (lacking this degeneracy) with its inverted copy. Using simple models, we unravel the evolution of local spin splitting during this process of inversion symmetry restoration, in the presence of spin-orbit interaction and sublattice coupling. Importantly, through an analysis of quantum mechanical commutativity, we examine the difficulty of identifying states that are simultaneously spatially segregated and spin polarized. We also explain how surface-sensitive experimental probes (such as angle-resolved photoemission spectroscopy, or ARPES) of "hidden spin polarization" in layered materials are susceptible to unrelated spin splitting intrinsically induced by broken inversion symmetry at the surface.

  10. Neutral Silicon-Vacancy Center in Diamond: Spin Polarization and Lifetimes

    Science.gov (United States)

    Green, B. L.; Mottishaw, S.; Breeze, B. G.; Edmonds, A. M.; D'Haenens-Johansson, U. F. S.; Doherty, M. W.; Williams, S. D.; Twitchen, D. J.; Newton, M. E.

    2017-09-01

    We demonstrate optical spin polarization of the neutrally charged silicon-vacancy defect in diamond (SiV0 ), an S =1 defect which emits with a zero-phonon line at 946 nm. The spin polarization is found to be most efficient under resonant excitation, but nonzero at below-resonant energies. We measure an ensemble spin coherence time T2>100 μ s at low-temperature, and a spin relaxation limit of T1>25 s . Optical spin-state initialization around 946 nm allows independent initialization of SiV0 and NV- within the same optically addressed volume, and SiV0 emits within the telecoms down-conversion band to 1550 nm: when combined with its high Debye-Waller factor, our initial results suggest that SiV0 is a promising candidate for a long-range quantum communication technology.

  11. Micromagnetism in (001) magnetite by spin-polarized low-energy electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Figuera, Juan de la, E-mail: juan.delafiguera@iqfr.csic.es [Instituto de Química-Física “Rocasolano”, CSIC, Madrid 28006 (Spain); Vergara, Lucía [Instituto de Química-Física “Rocasolano”, CSIC, Madrid 28006 (Spain); N' Diaye, Alpha T. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Quesada, Adrian [Instituto de Cerámica y Vidrio, CSIC, Calle Kelsen 5, 28049, Madrid (Spain); Schmid, Andreas K. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    2013-07-15

    Spin-polarized low-energy electron microscopy was used to image a magnetite crystal with (001) surface orientation. Sets of spin-dependent images of magnetic domain patterns observed in this surface were used to map the direction of the magnetization vector with high spatial and angular resolution. We find that domains are magnetized along the surface <110> directions, and domain wall structures include 90° and 180° walls. A type of unusually curved domain walls are interpreted as Néel-capped surface terminations of 180° Bloch walls. - Highlights: ► The (001) surface of magnetite is imaged by spin-polarized low-energy electron microscopy. ► The magnetic domain microstructure is resolved. ► Magnetic easy axes in this surface are found to be along <110> directions. ► Magnetic domain wall structures include wide Néel-caps.

  12. Improved Superlattices for Spin-Polarized Electron Sources

    Energy Technology Data Exchange (ETDEWEB)

    Mamaev, Yu.A.; Gerchikov, L.G.; Yashin, Yu.P.; Kuz-michev, V.; Vasiliev, D.; /St. Petersburg Polytechnic Inst.; Maruymama, T.; Clendenin, J.E.; /SLAC; Ustinov, V.M.; Zhukov, A.E.; /Ioffe Phys. Tech. Inst.

    2006-12-08

    Photoemission of polarized electrons from heterostructures based on InAlGaAs/GaAs superlattices with minimum conduction-band offsets is investigated. The comparison of the excitation energy dependence of the photoemission polarization degree with the calculated spectra makes it possible to determine the polarization losses at different stages of the photoemission. A maximum polarization of P = 91% and a quantum efficiency of QE = 0.5% are close to the best results obtained for photocathodes that are based on strained semiconductor superlattices.

  13. Recent advances in atomic-scale spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Smith, Arthur R; Yang, Rong; Yang, Haiqiang; Dick, Alexey; Neugebauer, Joerg; Lambrecht, Walter R L

    2005-02-01

    The Mn3N2 (010) surface has been studied using spin-polarized scanning tunneling microscopy at the atomic scale. The principle objective of this work is to elucidate the properties and potential of this technique to measure atomic-scale magnetic structures. The experimental approach involves the use of a combined molecular beam epitaxy/scanning tunneling microscopy system that allows the study of atomically clean magnetic surfaces. Several key findings have been obtained. First, both magnetic and non-magnetic atomic-scale information has been obtained in a single spin-polarized image. Magnetic modulation of the height profile having an antiferromagnetic super-period of c = 12.14 A (6 atomic rows) together with a non-magnetic superstructure having a period of c/2 = 6.07 A (3 atomic rows) was observed. Methods of separation of magnetic and non-magnetic profiles are presented. Second, bias voltage-dependent spin-polarized images show a reversal of the magnetic modulation at a particular voltage. This reversal is clearly due to a change in the sign of the magnetic term in the tunnel current. Since this term depends on both the tip's as well as the sample's magnetic local density of states, the reversal can be caused by either the sample or the tip. Third, the shape of the line profile was found to vary with the bias voltage, which is related to the energy-dependent spin contribution from the 2 chemically inequivalent Mn sites on the surface. Overall, the results shown here expand the application of the method of spin-polarized scanning tunneling microscopy to measure atomic-scale magnetic structures. (c) 2005 Wiley-Liss, Inc.

  14. Berry phase and shot noise for spin-polarized and entangled electrons

    International Nuclear Information System (INIS)

    Wang Pei; Tang Weihua; Lu Dinghui; Jiang Lixia; Zhao Xuean

    2007-01-01

    Shot noise for entangled and spin-polarized states in a four-probe geometric setup has been studied by adding two rotating magnetic fields in an incoming channel. Our results show that the noise power oscillates as the magnetic fields vary. The singlet, entangled triplet and polarized states can be distinguished by adjusting the magnetic fields. The Berry phase can be derived by measuring the shot noise power

  15. Application of the Ursell-Mayer method in the theory of spin-polarized atomic hydrogen

    International Nuclear Information System (INIS)

    Kilic, S.; Radelja, T.

    1981-01-01

    Employing the Ursell-Mayer method and Ljolje semi-free gas model analytic relations describing ground state properties (energy, pressure, compressibility, sound velocity, radial distribution function and one-particle density matrix) of spin-polarized atomic hydrogen were derived. The expressions are valid up to density 2 10 26 atoms/m 3 . It was found out that at density of 2 10 26 atoms/m 3 the condensation of particle in momentum space is 88% (at absolute zero). (orig.)

  16. Spin polarization in quantum dots by radiation field with circular polarization

    CERN Document Server

    Bulgakov, E N

    2001-01-01

    For circular quantum dot (QD) with account of the Razhba spin-orbit interaction (SOI) an exact energy spectrum is obtained. For the small SOI constant the Eigen functions of the QD are found. It is shown that application of radiation field with circular polarization lifts the Kramers degeneracy of the Eigen states of the QD. Effective spin polarization of transmitted electrons through the QD by radiation field with circular polarization is demonstrated

  17. Observation of interface dependent spin polarized photocurrents in InAs/GaSb superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yuan, E-mail: liyuan12@semi.ac.cn; Liu, Yu; Zhu, Laipan; Qin, Xudong; Wu, Qing; Huang, Wei; Chen, Yonghai, E-mail: yhchen@semi.ac.cn [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, 100083 Beijing (China); Niu, Zhichuan; Xiang, Wei; Hao, Hongyue [The State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, 100083 Beijing (China)

    2015-05-11

    In this letter, we investigated the spin polarized photocurrents excited by mid-infrared radiation and near-infrared radiation, respectively, in InAs/GaSb type II superlattices with different kinds of interfaces. By periodically varying the polarization state of the radiation, we analyzed Rashba-type and Dresselhaus-type spin polarized photocurrents, which present different features depending on the interface types and excitation conditions. Under mid-infrared excitation, the ratio of Rashba-type and Dresselhaus-type spin polarized photocurrents of the superlattice with InSb-like interface is obviously larger than that of the superlattice with GaAs-like interface, the ratio of the superlattice with alternate interface is in the middle. Whereas under near-infrared excitation, the ratios of the three superlattices are nearly the same. Further researches reveal the synactic effects of interface dependent strain and asymmetric interface potential on the spin splitting. Besides, the polarized Raman spectroscopies of these structures were also analyzed.

  18. Observation of interface dependent spin polarized photocurrents in InAs/GaSb superlattice

    International Nuclear Information System (INIS)

    Li, Yuan; Liu, Yu; Zhu, Laipan; Qin, Xudong; Wu, Qing; Huang, Wei; Chen, Yonghai; Niu, Zhichuan; Xiang, Wei; Hao, Hongyue

    2015-01-01

    In this letter, we investigated the spin polarized photocurrents excited by mid-infrared radiation and near-infrared radiation, respectively, in InAs/GaSb type II superlattices with different kinds of interfaces. By periodically varying the polarization state of the radiation, we analyzed Rashba-type and Dresselhaus-type spin polarized photocurrents, which present different features depending on the interface types and excitation conditions. Under mid-infrared excitation, the ratio of Rashba-type and Dresselhaus-type spin polarized photocurrents of the superlattice with InSb-like interface is obviously larger than that of the superlattice with GaAs-like interface, the ratio of the superlattice with alternate interface is in the middle. Whereas under near-infrared excitation, the ratios of the three superlattices are nearly the same. Further researches reveal the synactic effects of interface dependent strain and asymmetric interface potential on the spin splitting. Besides, the polarized Raman spectroscopies of these structures were also analyzed

  19. Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging.

    Science.gov (United States)

    Hauptmann, Nadine; Gerritsen, Jan W; Wegner, Daniel; Khajetoorians, Alexander A

    2017-09-13

    Storing and accessing information in atomic-scale magnets requires magnetic imaging techniques with single-atom resolution. Here, we show simultaneous detection of the spin-polarization and exchange force with or without the flow of current with a new method, which combines scanning tunneling microscopy and noncontact atomic force microscopy. To demonstrate the application of this new method, we characterize the prototypical nanoskyrmion lattice formed on a monolayer of Fe/Ir(111). We resolve the square magnetic lattice by employing magnetic exchange force microscopy, demonstrating its applicability to noncollinear magnetic structures for the first time. Utilizing distance-dependent force and current spectroscopy, we quantify the exchange forces in comparison to the spin-polarization. For strongly spin-polarized tips, we distinguish different signs of the exchange force that we suggest arises from a change in exchange mechanisms between the probe and a skyrmion. This new approach may enable both nonperturbative readout combined with writing by current-driven reversal of atomic-scale magnets.

  20. Investigation of Current Induced Spin Polarization in III-V Semiconductor Epilayers

    Science.gov (United States)

    Luengo-Kovac, Marta

    In the development of a semiconductor spintronics device, a thorough understanding of spin dynamics in semiconductors is necessary. In particular, electrical control of electron spins is advantageous for its compatibility with present day electronics. In this thesis, we will discuss the electrical modification of the electron g-factor, which characterizes the strength of the interaction between a spin and a magnetic field, as well as investigate electrically generated spin polarizations as a function of various material parameters. We report on the modification of the electron g-factor by an in-plane electric field in an InGaAs epilayer. We performed external magnetic field scans of the Kerr rotation of the InGaAs film in order to measure the g-factor independently of the spin-orbit fields. The g-factor increases from -0.4473(0.0001) at 0 V/cm to -0.4419( 0.0001) at 50 V/cm applied along the [110] crystal axis. A comparison of temperature and voltage dependent photoluminescence measurements indicate that minimal channel heating occurs at these voltages. Possible explanations for this g-factor modification are discussed, including an increase in the electron temperature that is independent of the lattice temperature and the modification of the donor-bound electron wave function by the electric field. The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InGaAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the spin polarization mechanism is extrinsic. Temperature-dependent measurements of the spin dephasing rates and mobilities were used to characterize the relative strengths of the intrinsic D

  1. Electron-spin polarization of photoions produced through photoionization from the laser-excited triplet state of Sr

    International Nuclear Information System (INIS)

    Yonekura, Nobuaki; Nakajima, Takashi; Matsuo, Yukari; Kobayashi, Tohru; Fukuyama, Yoshimitsu

    2004-01-01

    We report the detailed experimental study on the production of electron-spin-polarized Sr + ions through one-photon resonant two-photon ionization via laser-excited 5s5p 3 P 1 (M J =+1) of Sr atoms produced by laser-ablation. We have experimentally confirmed that the use of laser-ablation for the production of Sr atoms prior to photoionization does not affect the electron-spin polarization. We have found that the degree of electron-spin polarization is 64±9%, which is in good agreement with our recent theoretical prediction. As we discuss in detail, we infer, from a simple analysis, that photoelectrons, being the counterpart of electron-spin-polarized Sr + ions, have approximately the same degree of electron-spin polarization. Our experimental results demonstrate that the combined use of laser-ablation technique and pulsed lasers for photoionization would be a compact and effective way to realize a pulsed source for spin-polarized ions and electrons for the studies of various spin-dependent dynamics in chemical physics

  2. Magnetization switching of a metallic nanomagnet via current-induced surface spin-polarization of an underlying topological insulator

    International Nuclear Information System (INIS)

    Roy, Urmimala; Dey, Rik; Pramanik, Tanmoy; Ghosh, Bahniman; Register, Leonard F.; Banerjee, Sanjay K.

    2015-01-01

    We consider a thermally stable, metallic nanoscale ferromagnet (FM) subject to spin-polarized current injection and exchange coupling from the spin-helically locked surface states of a topological insulator (TI) to evaluate possible non-volatile memory applications. We consider parallel transport in the TI and the metallic FM, and focus on the efficiency of magnetization switching as a function of transport between the TI and the FM. Transport is modeled as diffusive in the TI beneath the FM, consistent with the mobility in the TI at room temperature, and in the FM, which essentially serves as a constant potential region albeit spin-dependent except in the low conductivity, diffusive limit. Thus, it can be captured by drift-diffusion simulation, which allows for ready interpretation of the results. We calculate switching time and energy consumed per write operation using self-consistent transport, spin-transfer-torque (STT), and magnetization dynamics calculations. Calculated switching energies and times compare favorably to conventional spin-torque memory schemes for substantial interlayer conductivity. Nevertheless, we find that shunting of current from the TI to a metallic nanomagnet can substantially limit efficiency. Exacerbating the problem, STT from the TI effectively increases the TI resistivity. We show that for optimum performance, the sheet resistivity of the FM layer should be comparable to or larger than that of the TI surface layer. Thus, the effective conductivity of the FM layer becomes a critical design consideration for TI-based non-volatile memory

  3. Measurement of transverse emittance at the source of spin-polarized electrons at the S-DALINAC

    Energy Technology Data Exchange (ETDEWEB)

    Eckardt, Christian; Barday, Roman; Bonnes, Uwe; Eichhorn, Ralf; Enders, Joachim; Hessler, Christoph; Patalakha, Oleksandr; Platz, Markus; Poltoratska, Yuliya; Rick, Wolfgang [Institut fuer Kernphysik, TU Darmstadt (Germany); Ackermann, Wolfgang; Mueller, Wolfgang F.O.; Steiner, Bastian; Weiland, Thomas [Institut fuer Theorie Elektromagnetischer Felder, TU Darmstadt (Germany)

    2008-07-01

    A new injector concept for 100 keV spin-polarized electrons (SPIN) at the S-DALINAC has been developed. The transverse emittance was measured for beam characterization. The emittance is a quantity concerning the quality of the beam, describing the phase space area. Determination of the emittance requires measurement of the beam profile and knowledge of the focal length of a beam focussing device. A wire scanner unit consisting of two 50 {mu}m diameter tungsten wires is used for the beam-profile measurement. Data analysis is performed by fitting a gaussian model distribution to estimate the 1{sigma} beam radius. Each determined beam width is correlated to the corresponding focal length of a magnetic lens, and a parabola fit is applied to calculate the parameters of the {sigma}-matrix. The square root of the determinant of the {sigma}-matrix defines the emittance. The results of the calculation are presented and the emittance is compared to theoretical estimates.

  4. Study of the nuclear structure far from stability: Coulomb excitation of neutron-rich Rb isotopes around N=60; Production of nuclear spin polarized beams using the tilted foils technique

    International Nuclear Information System (INIS)

    Sotty, C.

    2013-01-01

    The underlying structure in the region A ∼ 100, N ∼ 60 has been under intensive and extensive investigation, mainly by β-decay and γ-ray spectroscopy from fission processes. Around N ∼ 60, by adding just few neutrons, protons a rapid shape change occurs from spherical-like to well deformed g.s. shape. Shape coexistence has been observed in the Sr and Zr nuclei, and is expected to take place in the whole region. The mechanisms involved in the appearance of the deformation is not well understood. The interplay between down-sloping and up-sloping neutron Nilsson orbital is evoked as one of the main reasons for the sudden shape change. However, a clear identification of the active proton and neutron orbitals was still on-going. For that purpose, the neutron rich 93;95;97;99 Rb isotopes have been studied by Coulomb excitation at CERN (ISOLDE) using the REX-ISOLDE post-accelerator and the MINIBALL setup. The completely unknown structures of 97;99 Rb have been populated and observed. Prompt γ-ray coincidences of low-lying states have been observed and time-correlated in order to build level schemes. The associated transition strengths have been extracted with the GOSIA code. The observed matrix elements of the electromagnetic operator constituted new inputs of further theoretical calculations giving new insight on the involved orbitals. The sensitivity of such experiment can be increased using nuclear spin polarized radioactive ion beam. For that purpose the Tilted Foils Technique (TFT) of polarization has been investigated at CERN. This technique consists to spin polarize the ion beam, passing through thin foils tilted at an oblique angle with respect to the beam direction. The initially obtained atomic polarization is transferred to the nucleus by hyperfine interaction. This technique does not depend on the chemical nature of the element. Short lived nuclei can be polarized in-flight without any need to be stopped in a catcher. It opens up the possibility to

  5. A cryostat to hold frozen-spin polarized HD targets in CLAS: HDice-II

    International Nuclear Information System (INIS)

    The design, fabrication, operation, and performance of a 3/4 He dilution refrigerator and superconducting magnet system for holding a frozen-spin polarized hydrogen deuteride target in the Jefferson Laboratory CLAS detector during photon beam running is reported. The device operates both vertically (for target loading) and horizontally (for target bombardment). The device proves capable of maintaining a base temperature of 50 mK and a holding field of 1 T for extended periods. These characteristics enabled multi-month polarization lifetimes for frozen spin HD targets having proton polarization of up to 50% and deuteron up to 27%.

  6. A cryostat to hold frozen-spin polarized HD targets in CLAS: HDice-II

    Energy Technology Data Exchange (ETDEWEB)

    Lowry, M.M., E-mail: mlowry@jlab.org [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Bass, C.D. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); D' Angelo, A. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Universita' di Roma ‘Tor Vergata’, and INFN Sezione di Roma ‘Tor Vergata’, Via della Ricerca Scientifica, 1, I-00133 Roma (Italy); Deur, A.; Dezern, G. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Hanretty, C. [University of Virginia, 1400 University Avenue, Charlottesville, VA 22903 (United States); Ho, D. [Carnegie-Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States); Kageya, T.; Kashy, D. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Khandaker, M. [Norfolk State University, 700 Park Avenue, Norfolk, VA 23504 (United States); Laine, V. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Université Blaise Pascal, 34 Avenue Carnot, 63000 Clermont-Ferrand (France); O' Connell, T. [University of Connecticut, 115 N Eagleville Road, Storrs-Mansfield, CT 06269 (United States); Pastor, O. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Peng, P. [University of Virginia, 1400 University Avenue, Charlottesville, VA 22903 (United States); Sandorfi, A.M. [Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606 (United States); Sokhan, D. [Institut de Physique Nucleaire, Bat 100 – M053, Orsay 91406 (France); and others

    2016-04-11

    The design, fabrication, operation, and performance of a {sup 3/4}He dilution refrigerator and superconducting magnet system for holding a frozen-spin polarized hydrogen deuteride target in the Jefferson Laboratory CLAS detector during photon beam running is reported. The device operates both vertically (for target loading) and horizontally (for target bombardment). The device proves capable of maintaining a base temperature of 50 mK and a holding field of 1 T for extended periods. These characteristics enabled multi-month polarization lifetimes for frozen spin HD targets having proton polarization of up to 50% and deuteron up to 27%.

  7. Low energy spin polarized radioactive beams as a probe of thin films and interfaces

    CERN Document Server

    Kiefl, R F; Amaudruz, P A; Arseneau, D; Baartman, R; Beals, T R; Behr, J; Brewer, J; Daviel, S; Hatakeyama, A; Hitti, B; Kreitzman, S R; Levy, C D P; Miller, R; Olivo, M; Poutissou, R; Morris, G D; Dunsiger, S R; Heffner, R; Chow, K H; Hirayama, Y; Izumi, H; Bommas, C; Dumont, E; Greene, L H

    2003-01-01

    A spectrometer for beta-detected nuclear magnetic resonance (beta-NMR) has been commissioned at the ISAC facility at TRIUMF. A beam of low energy highly spin polarized sup 8 Li sup + can be decelerated and implanted into ultra-thin structures 6-400 nm thick. beta-NMR provides local information on the electronic and magnetic properties of materials which is similar to conventional NMR but can be used as a sensitive probe of ultra-thin films, interfaces and other nanostructures. We report here on the status of the spectrometer and preliminary results on a simple metal film.

  8. Light-free magnetic resonance force microscopy for studies of electron spin polarized systems

    International Nuclear Information System (INIS)

    Pelekhov, Denis V.; Selcu, Camelia; Banerjee, Palash; Chung Fong, Kin; Chris Hammel, P.; Bhaskaran, Harish; Schwab, Keith

    2005-01-01

    Magnetic resonance force microscopy is a scanned probe technique capable of three-dimensional magnetic resonance imaging. Its excellent sensitivity opens the possibility for magnetic resonance studies of spin accumulation resulting from the injection of spin polarized currents into a para-magnetic collector. The method is based on mechanical detection of magnetic resonance which requires low noise detection of cantilever displacement; so far, this has been accomplished using optical interferometry. This is undesirable for experiments on doped silicon, where the presence of light is known to enhance spin relaxation rates. We report a non-optical displacement detection scheme based on sensitive microwave capacitive readout

  9. Observation of nuclear spin waves in spin-polarized atomic hydrogen gas

    Energy Technology Data Exchange (ETDEWEB)

    Johson, B.R.; Denker, J.S.; Bigelow, N.; Levy, L.P.; Freed, J.H.; Lee, D.M.

    1984-04-23

    We have observed narrow, distinct resonances in the NMR spectrum of dilute spin-polarized atomic hydrogen gas (nroughly-equal10/sup 16/ atoms/cm/sup 3/). The dependence of the observed spectra on temperature, density, polarization, and magnetic field gradient is consistent with theoretical predictions for spin-wave excitations damped by diffusion. We have measured the parameter ..mu.., which is a measure of the importance of exchange effects in spin transport processes, and the diffusion coefficient D/sub 0/, both of which are in reasonable agreement with theory.

  10. Photoemission of Bi_{2}Se_{3} with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?

    Directory of Open Access Journals (Sweden)

    J. Sánchez-Barriga

    2014-03-01

    Full Text Available Topological insulators are characterized by Dirac-cone surface states with electron spins locked perpendicular to their linear momenta. Recent theoretical and experimental work implied that this specific spin texture should enable control of photoelectron spins by circularly polarized light. However, these reports questioned the so far accepted interpretation of spin-resolved photoelectron spectroscopy. We solve this puzzle and show that vacuum ultraviolet photons (50–70 eV with linear or circular polarization indeed probe the initial-state spin texture of Bi_{2}Se_{3} while circularly polarized 6-eV low-energy photons flip the electron spins out of plane and reverse their spin polarization, with its sign determined by the light helicity. Our photoemission calculations, taking into account the interplay between the varying probing depth, dipole-selection rules, and spin-dependent scattering effects involving initial and final states, explain these findings and reveal proper conditions for light-induced spin manipulation. Our results pave the way for future applications of topological insulators in optospintronic devices.

  11. Simultaneous production of spin-polarized ions/electrons based on two-photon ionization of laser-ablated metallic atoms

    International Nuclear Information System (INIS)

    Nakajima, Takashi; Yonekura, Nobuaki; Matsuo, Yukari; Kobayashi, Tohru; Fukuyama, Yoshimitsu

    2003-01-01

    We demonstrate the simultaneous production of spin-polarized ions/electrons using two-color, two-photon ionization of laser-ablated metallic atoms. Specifically, we have applied the developed technique to laser-ablated Sr atoms, and found that the electron-spin polarization of Sr + ions, and accordingly, the spin polarization of photoelectrons is 64%±9%, which is in good agreement with the theoretical prediction we have recently reported [T. Nakajima and N. Yonekura, J. Chem. Phys. 117, 2112 (2002)]. Our experimental results open up a simple way toward the construction of a spin-polarized dual ion/electron source

  12. Effect of Orbital Hybridization on Spin-Polarized Tunneling across Co/C60 Interfaces.

    Science.gov (United States)

    Wang, Kai; Strambini, Elia; Sanderink, Johnny G M; Bolhuis, Thijs; van der Wiel, Wilfred G; de Jong, Michel P

    2016-10-26

    The interaction between ferromagnetic surfaces and organic semiconductors leads to the formation of hybrid interfacial states. As a consequence, the local magnetic moment is altered, a hybrid interfacial density of states (DOS) is formed, and spin-dependent shifts of energy levels occur. Here, we show that this hybridization affects spin transport across the interface significantly. We report spin-dependent electronic transport measurements for tunnel junctions comprising C 60 molecular thin films grown on top of face-centered-cubic (fcc) epitaxial Co electrodes, an AlO x tunnel barrier, and an Al counter electrode. Since only one ferromagnetic electrode (Co) is present, spin-polarized transport is due to tunneling anisotropic magnetoresistance (TAMR). An in-plane TAMR ratio of approximately 0.7% has been measured at 5 K under application of a magnetic field of 800 mT. The magnetic switching behavior shows some remarkable features, which are attributed to the rotation of interfacial magnetic moments. This behavior can be ascribed to the magnetic coupling between the Co thin films and the newly formed Co/C 60 hybridized interfacial states. Using the Tedrow-Meservey technique, the tunnel spin polarization of the Co/C 60 interface was found to be 43%.

  13. Spin-polarized radioactive isotope beam produced by tilted-foil technique

    International Nuclear Information System (INIS)

    Hirayama, Yoshikazu; Mihara, Mototsugu; Watanabe, Yutaka; Jeong, Sun-Chan; Miyatake, Hiroari; Momota, Sadao; Hashimoto, Takashi; Imai, Nobuaki; Matsuta, Kensaku; Ishiyama, Hironobu; Ichikawa, Shin-ichi; Ishii, Tetsuro; Izumikawa, Takuji; Katayama, Ichiro; Kawakami, Hirokane; Kawamura, Hirokazu; Nishinaka, Ichiro; Nishio, Katsuhisa; Makii, Hiroyuki; Mitsuoka, Shin-ichi

    2013-01-01

    Highlights: • Detail study for tilted foil technique. • New equation for estimating nuclear polarization dependence on the beam energy. • Production of nuclear polarization for heaviest nucleus 123 In in ground state. -- Abstract: The tilted-foil method for producing spin-polarized radioactive isotope beams has been studied using the re-accelerated radioactive 8 Li and 123 In beams produced at Tokai Radioactive Ion Accelerator Complex (TRIAC) facility. We successfully produced polarization in a 8 Li beam of 7.3(5)% using thin polystyrene foils (4.2 μg/cm 2 ). The systematic study of the nuclear polarization as a function of the number of foils and beam energy has been performed, confirming the features of the tilted-foil technique experimentally. After the study, a spin-polarized radioactive 123 In beam, which is the heaviest ever polarized in its ground state by this method, has been successfully generated by the tilted-foil method, for the nuclear spectroscopy around the doubly magic nucleus 132 Sn

  14. Construction and characterization of a spin polarized helium ion beam for surface electronic structure studies

    International Nuclear Information System (INIS)

    Harrison, A.R.

    1982-01-01

    Ion neutralization and metastable de-excitation spectroscopy, INS and MDS, allow detailed analysis of the surface electronic configuration of metals. The orthodox application of these spectroscopies may be enhanced by electronic spin polarization of the probe beams. For this reason, a spin polarized helium ion beam has been constructed. The electronic spin of helium metastables created within an rf discharge may be spacially aligned by optically pumping the atoms. Subsequent collisions between metastables produce helium ions which retain the orientation of the electronic spin. Extracted ion polarization, although not directly measurable, may be estimated from extracted electron polarization, metastable polarization, pumping radiation absorption and current modulation measurements. Ions extracted from the optically pumped discharge exhibit an estimated polarization of about ten per cent at a beam current of a few tenths of a microampere. Extraction of helium ions from the discharge requires that the ions have a high kinetic energy. However, to avoid undesirable kinetic electron ejection from the target surface, the ions must be decelerated. Examination of various deceleration configurations, in paticular exponential and linear deceleration fields, and experimental observation indicate that a linear decelerating field produces the best low energy beam to the target surface

  15. Tunable spin-polarized edge transport in inverted quantum-well junctions

    Science.gov (United States)

    Nanclares, Dimy; Lima, Leandro R. F.; Lewenkopf, Caio H.; da Silva, Luis G. G. V. Dias

    2017-10-01

    Inverted HgTe/CdTe quantum wells have been used as a platform for the realization of two-dimensional topological insulators, bulk insulator materials with spin-helical metallic edge states protected by time-reversal symmetry. This paper investigates the spectrum and the charge transport in HgTe/CdTe quantum well junctions both in the topological regime and in the absence of time-reversal symmetry. We model the system using the Bernevig-Hughes-Zhang effective Hamiltonian and compute the transport properties using recursive Green's functions with a finite differences' method. Specifically, we have studied the material's spatially resolved conductance in a setup with a gated central region, forming monopolar (n -n'-n ) and heteropolar (n -p -n , n -TI-n ) double junctions, which have been recently realized in experiments. We find regimes in which the edge states carry spin-polarized currents in the central region even in the presence of a small magnetic field, which breaks time-reversal symmetry. More interestingly, the conductance displays spin-dependent, Fabry-Perót-like oscillations as a function of the central gate voltage producing tunable, fully spin-polarized currents through the device.

  16. Magnetic adatoms in two and four terminal graphene nanoribbons: A comparison between their spin polarized transport

    Science.gov (United States)

    Ganguly, Sudin; Basu, Saurabh

    2018-04-01

    We study the charge and spin transport in two and four terminal graphene nanoribbons (GNR) decorated with random distribution of magnetic adatoms. The inclusion of the magnetic adatoms generates only the z-component of the spin polarized conductance via an exchange bias in the absence of Rashba spin-orbit interaction (SOI), while in presence of Rashba SOI, one is able to create all the three (x, y and z) components. This has important consequences for possible spintronic applications. The charge conductance shows interesting behaviour near the zero of the Fermi energy. Where in presence of magnetic adatoms the familiar plateau at 2e2 / h vanishes, thereby transforming a quantum spin Hall insulating phase to an ordinary insulator. The local charge current and the local spin current provide an intuitive idea on the conductance features of the system. We found that, the local charge current is independent of Rashba SOI, while the three components of the local spin currents are sensitive to Rashba SOI. Moreover the fluctuations of the spin polarized conductance are found to be useful quantities as they show specific trends, that is, they enhance with increasing adatom densities. A two terminal GNR device seems to be better suited for possible spintronic applications.

  17. Stability of superfluid phases in the 2D spin-polarized attractive Hubbard model

    Science.gov (United States)

    Kujawa-Cichy, A.; Micnas, R.

    2011-08-01

    We study the evolution from the weak coupling (BCS-like limit) to the strong coupling limit of tightly bound local pairs (LPs) with increasing attraction, in the presence of the Zeeman magnetic field (h) for d=2, within the spin-polarized attractive Hubbard model. The broken symmetry Hartree approximation as well as the strong coupling expansion are used. We also apply the Kosterlitz-Thouless (KT) scenario to determine the phase coherence temperatures. For spin-independent hopping integrals (t↑=t↓), we find no stable homogeneous polarized superfluid (SCM) state in the ground state for the strong attraction and obtain that for a two-component Fermi system on a 2D lattice with population imbalance, phase separation (PS) is favoured for a fixed particle concentration, even on the LP (BEC) side. We also examine the influence of spin-dependent hopping integrals (mass imbalance) on the stability of the SCM phase. We find a topological quantum phase transition (Lifshitz type) from the unpolarized superfluid phase (SC0) to SCM and tricritical points in the h-|U| and t↑/t↓-|U| ground-state phase diagrams. We also construct the finite temperature phase diagrams for both t↑=t↓ and t↑≠t↓ and analyze the possibility of occurrence of a spin-polarized KT superfluid.

  18. Spin-polarized semiconductors: tuning the electronic structure of graphene by introducing a regular pattern of sp3 carbons on the graphene plane.

    Science.gov (United States)

    Jing, Long; Huang, Ping; Zhu, Huarui; Gao, Xueyun

    2013-01-28

    First-principles calculations (generalized gradient approximation, density functional therory (DFT) with dispersion corrections, and DFT plus local atomic potential) are carried out on the stability and electronic structures of superlattice configurations of nitrophenyl diazonium functionalized graphene with different coverage. In the calculations, the stabilities of these structures are strengthened significantly since van der Waals interactions between nitrophenyl groups are taken into account. Furthermore, spin-polarized and wider-bandgap electronic structures are obtained when the nitrophenyl groups break the sublattice symmetry of the graphene. The unpaired quasi-localized p electrons are responsible for this itinerant magnetism. The results provide a novel approach to tune graphene's electronic structures as well as to form ferromagnetic semiconductive graphene. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Relativistic spin-polarized KKR theory for superconducting heterostructures: Oscillating order parameter in the Au layer of Nb/Au/Fe trilayers

    Science.gov (United States)

    Csire, Gábor; Deák, András; Nyári, Bendegúz; Ebert, Hubert; Annett, James F.; Újfalussy, Balázs

    2018-01-01

    The fully relativistic spin-polarized multiple-scattering theory is developed for inhomogeneous superconductors, including superconducting/normal-metal/ferromagnet heterostructures. The method allows the solution of the first-principles Dirac-Bogoliubov-de Gennes equations combined with a semiphenomenological parametrization of the exchange-correlation functional. Simple conditions are derived for the case when the right-hand-side and left-hand-side solutions must be treated separately when setting up the corresponding Green's function. As an application of the theory, we calculate the order parameters of Nb/Fe and Nb/Au/Fe systems. We find Fulde-Ferrell-Larkin-Ovchinnikov-like oscillations in the iron layers, but more interestingly an oscillatory behavior is observed in the gold layers as well. The band-structure calculations suggest that this is the consequence of an interplay between the quantum-well states and ferromagnetism.

  20. Improved Electron Yield and Spin-Polarization from III-V Photocathodes via Bias Enhanced Carrier Drift: Final Report

    International Nuclear Information System (INIS)

    Mulhollan, Gregory A.

    2006-01-01

    In this DOE STTR program, Saxet Surface Science, with the Stanford Linear Accelerator Center as partner, designed, built and tested photocathode structures such that optimal drift-enhanced spin-polarization from GaAs based photoemitters was achieved with minimal bias supply requirements. The forward bias surface grid composition was optimized for maximum polarization and yield, together with other construction parameters including doping profile. This program has culminated in a cathode bias structure affording increased electron spin polarization when applied to III-V based photocathodes. The optimized bias structure has been incorporated into a cathode mounting and biasing design for use in a polarized electron gun.

  1. Electron spin injection from a regrown Fe layer in a spin-polarized vertical-cavity surface-emitting laser

    Science.gov (United States)

    Holub, M.; Bhattacharya, P.; Shin, J.; Saha, D.

    2007-04-01

    An electroluminescence circular polarization of 23% and threshold current reduction of 11% are obtained in an electrically pumped spin-polarized vertical-cavity surface-emitting laser. Electron spin injection is accomplished utilizing a regrown Fe/ n-AlGaAs Schottky tunnel barrier deposited around the base of the laser mesas. Negligible circular polarizations and threshold current reductions are measured for nonmagnetic and Fe-based control VCSELs, which provides convincing evidence of spin injection, transport, and detection in our spin-polarized laser.

  2. Reduced interface spin polarization by antiferromagnetically coupled Mn segregated to the C o2MnSi /GaAs (001) interface

    Science.gov (United States)

    Rath, Ashutosh; Sivakumar, Chockalingam; Sun, C.; Patel, Sahil J.; Jeong, Jong Seok; Feng, J.; Stecklein, G.; Crowell, Paul A.; Palmstrøm, Chris J.; Butler, William H.; Voyles, Paul M.

    2018-01-01

    We have investigated the interfacial structure and its correlation with the calculated spin polarization in C o2MnSi /GaAs(001) lateral spin valves. C o2MnSi (CMS) films were grown on As-terminated c(4 ×4 ) GaAs(100) by molecular beam epitaxy using different first atomic layers: MnSi, Co, and Mn. Atomically resolved Z -contrast scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) were used to develop atomic structural models of the CMS/GaAs interfaces that were used as inputs for first-principles calculations to understand the magnetic and electronic properties of the interface. First-principles structures were relaxed and then validated by comparing experimental and simulated high-resolution STEM images. STEM-EELS results show that all three films have similar six atomic layer thick, Mn- and As-rich multilayer interfaces. However, the Co-initiated interface contains a M n2As -like layer, which is antiferromagnetic, and which is not present in the other two interfaces. Density functional theory calculations show a higher degree of interface spin polarization in the Mn- and MnSi-initiated cases, compared to the Co-initiated case, although none of the interfaces are half-metallic. The loss of half-metallicity is attributed, at least in part, to the segregation of Mn at the interface, which leads to the formation of interface states. The implications for the performance of lateral spin valves based on these interfaces are discussed briefly.

  3. Spin-polarized x-ray emission of 3d transition-metal ions : A comparison via K alpha and K beta detection

    NARCIS (Netherlands)

    Wang, Xin; deGroot, F.M.F.; Cramer, SP

    1997-01-01

    This paper demonstrates that spin-polarized x-ray-excitation spectra can be obtained using K alpha emission as well as K beta lines. A spin-polarized analysis of K alpha x-ray emission and the excitation spectra by K alpha detection on a Ni compound is reported. A systematic analysis of the

  4. Dark states in spin-polarized transport through triple quantum dot molecules

    Science.gov (United States)

    Wrześniewski, K.; Weymann, I.

    2018-02-01

    We study the spin-polarized transport through a triple-quantum-dot molecule weakly coupled to ferromagnetic leads. The analysis is performed by means of the real-time diagrammatic technique, including up to the second order of perturbation expansion with respect to the tunnel coupling. The emphasis is put on the impact of dark states on spin-resolved transport characteristics. It is shown that the interplay of coherent population trapping and cotunneling processes results in a highly nontrivial behavior of the tunnel magnetoresistance, which can take negative values. Moreover, a super-Poissonian shot noise is found in transport regimes where the current is blocked by the formation of dark states, which can be additionally enhanced by spin dependence of tunneling processes, depending on the magnetic configuration of the device. The mechanisms leading to those effects are thoroughly discussed.

  5. Spin-polarized scanning-tunneling probe for helical Luttinger liquids.

    Science.gov (United States)

    Das, Sourin; Rao, Sumathi

    2011-06-10

    We propose a three-terminal spin-polarized STM setup for probing the helical nature of the Luttinger liquid edge state that appears in the quantum spin Hall system. We show that the three-terminal tunneling conductance depends on the angle (θ) between the magnetization direction of the tip and the local orientation of the electron spin on the edge while the two terminal conductance is independent of this angle. We demonstrate that chiral injection of an electron into the helical Luttinger liquid (when θ is zero or π) is associated with fractionalization of the spin of the injected electron in addition to the fractionalization of its charge. We also point out a spin current amplification effect induced by the spin fractionalization.

  6. Theoretical consideration of spin-polarized resonant tunneling in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Mu Haifeng; Zhu Zhengang; Zheng Qingrong; Jin Biao; Wang Zhengchuan; Su Gang

    2004-01-01

    A recent elegant experimental realization [S. Yuasa et al., Science 297 (2002) 234] of the spin-polarized resonant tunneling in magnetic tunnel junctions is interpreted in terms of a two-band model. It is shown that the tunnel magnetoresistance (TMR) decays oscillatorily with the thickness of the normal metal (NM) layer, being fairly in agreement with the experimental observation. The tunnel conductance is found to decay with slight oscillations with the increase of the NM layer thickness, which is also well consistent with the experiment. In addition, when the magnetizations of both ferromagnet electrodes are not collinearly aligned, TMR is found to exhibit sharp resonant peaks at some particular thickness of the NM layer. The peaked TMR obeys nicely a Gaussian distribution against the relative orientation of the magnetizations

  7. Spin polarized solid target as a prospective tool for radioactive ion beam physics

    Science.gov (United States)

    Urrego-Blanco, J. P.; van den Brandt, B.; Bunyatova, E. I.; Galindo-Uribarri, A.; Hautle, P.; Konter, J. A.

    2005-12-01

    Spin polarized probes are used in a wide range of experiments in nuclear physics including the determination of spin structure functions and tests of fundamental symmetries. At low energies, light stable polarized beams have been used for spectroscopic purposes. We propose to extend these types of experiments to nuclei far from stability by using radioactive ion beams (RIBs) and polarized targets. Towards this goal we intend to develop a solid polarized proton and/or deuterium target in the thickness range between 20 μm and 100 μm based on a scintillating (active) polymeric foil. Such a target would be a useful tool in the determination of excitation functions in resonant reactions, in studies of one-nucleon transfer reactions using RIBs as well as in probing the matter density of atomic nuclei. If scintillating, it could also help remove the background associated with the scattering of the radioactive beam.

  8. Spin polarized solid target as a prospective tool for radioactive ion beam physics

    Energy Technology Data Exchange (ETDEWEB)

    Urrego-Blanco, J.P. [Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States); Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6371 (United States); Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Brandt, B. van den [Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Bunyatova, E.I. [Joint Institute for Nuclear Research, Dubna, Head P.O. Box 79, 101000 Moscow (Russian Federation); Galindo-Uribarri, A. [Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6371 (United States)]. E-mail: uribarri@mail.phy.ornl.gov; Hautle, P. [Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Konter, J.A. [Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland)

    2005-12-15

    Spin polarized probes are used in a wide range of experiments in nuclear physics including the determination of spin structure functions and tests of fundamental symmetries. At low energies, light stable polarized beams have been used for spectroscopic purposes. We propose to extend these types of experiments to nuclei far from stability by using radioactive ion beams (RIBs) and polarized targets. Towards this goal we intend to develop a solid polarized proton and/or deuterium target in the thickness range between 20 {mu}m and 100 {mu}m based on a scintillating (active) polymeric foil. Such a target would be a useful tool in the determination of excitation functions in resonant reactions, in studies of one-nucleon transfer reactions using RIBs as well as in probing the matter density of atomic nuclei. If scintillating, it could also help remove the background associated with the scattering of the radioactive beam.

  9. Observation of radiative spin-polarization at 60.6 GeV

    CERN Document Server

    Assmann, R W; Hildreth, M D; Matheson, J; Mugnai, G; Placidi, Massimo; Roncarolo, F; Torrence, E; Sonnemann, F; Uythoven, J; Wenninger, J; Blondel, A

    1999-01-01

    Radiative spin-polarization has been used extensively at LEP to accurately measure the beam energy around the Z resonance. As the LEP physics has moved on to the W boson the calibration based on polarization must be extended towards higher beam energies. This is difficult as the depolarizing effects of spin resonances grow rapidly with beam energy. At LEP it has been possible for the first time to measure transverse beam polarization at 60.6 GeV. To allow a build-up of polarization the tunes and the energy were chosen accurately. A low phase advance optics was used and careful orbit correction was carried out using dynamic beam based alignment data. Harmonic spin matching was applied both in a deterministic and a novel semi- empirical way. (11 refs).

  10. Coexistence of antiferromagnetism and spin polarization in double perovskite SrLaVMoO6

    International Nuclear Information System (INIS)

    Asano, H; Gotoh, H; Matsushima, H; Takeda, Y; Zhong, J; Rajanikanth, A; Hono, K

    2010-01-01

    The magnetic and transport properties of SrLaVMoO 6 bulk samples with an ordered double perovskite structure have been investigated. Magnetization measurements have indicated that the SrLaVMoO 6 compound exhibits a cusp at 125 K, which is attributable to an antiferromagnetic transition. Electrical resistivity ρ for the compound showed metallic temperature dependence from 10 to 300 K, and a spin polarization P value was measured to be 0.50 using the point-contact Andreev reflection (PCAR) technique. It has been found from X-ray photoemission spectroscopy (XPS) study that SrLaVMoO 6 closely resembles the half-metallic Sr 2 FeMoO 6 in the electronic state of the Mo.

  11. Nuclear spin polarized alkali beams (Na, Li): Optical pumping with electro-optically modulated laser beam

    International Nuclear Information System (INIS)

    Reich, H.; Jaensch, H.J.

    1990-01-01

    An improvement of the Heidelberg source for polarized heavy ions (PSI) is described. To produce a nuclear spin polarized atomic Na beam an electro-optically modulated laser beam has been used for optical pumping. An electro-optic modulator (EOM) was constructed with a bandwidth of 1.8 GHz. Without a spin separating Stern-Gerlach magnet it is now possible to prepare a Na atomic beam in one single hyperfine magnetic substate. Thus the beam figure of merit (polarization 2 x intensity of the beam) has been improved by a factor of 4 as compared to the previous setup. Experiences with the new system collected from several beam times are discussed. (orig.)

  12. Dirac cone with helical spin polarization in ultrathin α-Sn(001) films.

    Science.gov (United States)

    Ohtsubo, Yoshiyuki; Le Fèvre, Patrick; Bertran, François; Taleb-Ibrahimi, Amina

    2013-11-22

    Spin-split two-dimensional electronic states have been observed on ultrathin Sn(001) films grown on InSb(001) substrates. Angle-resolved photoelectron spectroscopy (ARPES) performed on these films revealed Dirac-cone-like linear dispersion around the Γ¯ point of the surface Brillouin zone, suggesting nearly massless electrons belonging to 2D surface states. The states disperse across a band gap between bulklike quantum well states in the films. Moreover, both circular dichroism of ARPES and spin-resolved ARPES studies show helical spin polarization of the Dirac-cone-like surface states, suggesting a topologically protected character as in a bulk topological insulator (TI). These results indicate that a quasi-3D TI phase can be realized in ultrathin films of zero-gap semiconductors.

  13. Lateral-electric-field-induced spin polarization in a suspended GaAs quantum point contact

    Science.gov (United States)

    Pokhabov, D. A.; Pogosov, A. G.; Zhdanov, E. Yu.; Shevyrin, A. A.; Bakarov, A. K.; Shklyaev, A. A.

    2018-02-01

    The conductance of a GaAs-based suspended quantum point contact (QPC) equipped with lateral side gates has been experimentally studied in the absence of the external magnetic field. The half-integer conductance plateau ( 0.5 ×2 e2/h ) has been observed when an asymmetric voltage between the side gates is applied. The appearance of this plateau has been attributed to the spin degeneracy lifting caused by the spin-orbit coupling associated with the lateral electric field in the asymmetrically biased QPC. We have experimentally demonstrated that, despite the relatively small g-factor in GaAs, the observation of the spin polarization in the GaAs-based QPC became possible after the suspension due to the enhancement of the electron-electron interaction and the effect of the electric field guiding. These features are caused by a partial confinement of the electric field lines within a suspended semiconductor layer with a high dielectric constant.

  14. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation.

    Science.gov (United States)

    Ceeh, Hubert; Weber, Josef Andreas; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph

    2016-02-16

    We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV.

  15. Real-space observation of a right-rotating inhomogeneous cycloidal spin spiral by spin-polarized scanning tunneling microscopy in a triple axes vector magnet.

    Science.gov (United States)

    Meckler, S; Mikuszeit, N; Pressler, A; Vedmedenko, E Y; Pietzsch, O; Wiesendanger, R

    2009-10-09

    Using spin-polarized scanning tunneling microscopy performed in a triple axes vector magnet, we show that the magnetic structure of the Fe double layer on W(110) is an inhomogeneous right-rotating cycloidal spin spiral. The magnitude of the Dzyaloshinskii-Moriya vector is extracted from the experimental data using micromagnetic calculations. The result is confirmed by comparison of the measured saturation field along the easy axis to the respective value as obtained from Monte Carlo simulations. We find that the Dzyaloshinskii-Moriya interaction is too weak to destabilize the single domain state. However, it can define the sense of rotation and the cycloidal spiral type once the single domain state is destabilized by dipolar interaction.

  16. Strain effects on the spin polarized electron gas in ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures

    KAUST Repository

    Nazir, Safdar

    2013-04-11

    The spin polarized two dimensional electron gas in the correlated ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures is investigated by ab-initio calculations using density functional theory. Structural relaxation shows a strong buckling at and near the TiO2 terminated n-type interface (IFs) due to significant TiO6 octahedral distortions. We find in all cases, metallic states in a very narrow region of the SrTiO3, in agreement with experimental results. We demonstrate that the interface magnetism strongly reacts to the magnitude of the lattice strain. The orbital occupations and, hence, the charge carrier density change systematically as a function of the lattice mismatch between the component materials.

  17. Shape coexistence in the N=19 neutron-rich nucleus 31Mg explored by β–γ spectroscopy of spin-polarized 31Na

    Directory of Open Access Journals (Sweden)

    H. Nishibata

    2017-04-01

    Full Text Available The structure of excited states in the neutron-rich nucleus 31Mg, which is in the region of the “island of inversion” associated with the neutron magic number N=20, is studied by β–γ spectroscopy of spin-polarized 31Na. Among the 31Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with Kπ=1/2+ and 1/2− are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD plus generator coordinate method (GCM. It is found that various nuclear structures coexist in the low excitation energy region in 31Mg.

  18. How to decide? Different methods of calculating gene expression from short oligonucleotide array data will give different results

    Directory of Open Access Journals (Sweden)

    Voesenek Laurentius ACJ

    2006-03-01

    Full Text Available Abstract Background Short oligonucleotide arrays for transcript profiling have been available for several years. Generally, raw data from these arrays are analysed with the aid of the Microarray Analysis Suite or GeneChip Operating Software (MAS or GCOS from Affymetrix. Recently, more methods to analyse the raw data have become available. Ideally all these methods should come up with more or less the same results. We set out to evaluate the different methods and include work on our own data set, in order to test which method gives the most reliable results. Results Calculating gene expression with 6 different algorithms (MAS5, dChip PMMM, dChip PM, RMA, GC-RMA and PDNN using the same (Arabidopsis data, results in different calculated gene expression levels. Consequently, depending on the method used, different genes will be identified as differentially regulated. Surprisingly, there was only 27 to 36% overlap between the different methods. Furthermore, 47.5% of the genes/probe sets showed good correlation between the mismatch and perfect match intensities. Conclusion After comparing six algorithms, RMA gave the most reproducible results and showed the highest correlation coefficients with Real Time RT-PCR data on genes identified as differentially expressed by all methods. However, we were not able to verify, by Real Time RT-PCR, the microarray results for most genes that were solely calculated by RMA. Furthermore, we conclude that subtraction of the mismatch intensity from the perfect match intensity results most likely in a significant underestimation for at least 47.5% of the expression values. Not one algorithm produced significant expression values for genes present in quantities below 1 pmol. If the only purpose of the microarray experiment is to find new candidate genes, and too many genes are found, then mutual exclusion of the genes predicted by contrasting methods can be used to narrow down the list of new candidate genes by 64 to 73%.

  19. Orientation and thickness dependence of magnetization at the interfacesof highly spin-polarized manganite thin films

    Energy Technology Data Exchange (ETDEWEB)

    Chopdekar, Rajesh V.; Arenholz, Elke; Suzuki, Y.

    2008-08-18

    We have probed the nature of magnetism at the surface of (001), (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films. The spin polarization of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films is not intrinsically suppressed at all surfaces and interfaces but is highly sensitive to both the epitaxial strain state as well as the substrate orientation. Through the use of soft x-ray spectroscopy, the magnetic properties of (001), (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interfaces have been investigated and compared to bulk magnetometry and resistivity measurements. The magnetization of (110) and (111)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interfaces are more bulk-like as a function of thickness whereas the magnetization at the (001)-oriented La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} interface is suppressed significantly below a layer thickness of 20 nm. Such findings are correlated with the biaxial strain state of the La{sub 0.7}Sr{sub 0.3}MnO{sub 3} films; for a given film thickness it is the tetragonal distortion of (001) La{sub 0.7}Sr{sub 0.3}MnO{sub 3} that severely impacts the magnetization, whereas the trigonal distortion for (111)-oriented films and monoclinic distortion for (110)-oriented films have less of an impact. These observations provide evidence that surface magnetization and thus spin polarization depends strongly on the crystal surface orientation as well as epitaxial strain.

  20. Theory of current-induced spin polarization in an electron gas

    Science.gov (United States)

    Gorini, Cosimo; Maleki Sheikhabadi, Amin; Shen, Ka; Tokatly, Ilya V.; Vignale, Giovanni; Raimondi, Roberto

    2017-05-01

    We derive the Bloch equations for the spin dynamics of a two-dimensional electron gas in the presence of spin-orbit coupling. For the latter we consider both the intrinsic mechanisms of structure inversion asymmetry (Rashba) and bulk inversion asymmetry (Dresselhaus), and the extrinsic ones arising from the scattering from impurities. The derivation is based on the SU(2) gauge-field formulation of the Rashba-Dresselhaus spin-orbit coupling. Our main result is the identification of a spin-generation torque arising from Elliot-Yafet scattering, which opposes a similar term arising from Dyakonov-Perel relaxation. Such a torque, which to the best of our knowledge has gone unnoticed so far, is of basic nature, i.e., should be effective whenever Elliott-Yafet processes are present in a system with intrinsic spin-orbit coupling, irrespective of further specific details. The spin-generation torque contributes to the current-induced spin polarization (CISP), also known as inverse spin-galvanic or Edelstein effect. As a result, the behavior of the CISP turns out to be more complex than one would surmise from consideration of the internal Rashba-Dresselhaus fields alone. In particular, the symmetry of the current-induced spin polarization does not necessarily coincide with that of the internal Rashba-Dresselhaus field, and an out-of-plane component of the CISP is generally predicted, as observed in recent experiments. We also discuss the extension to the three-dimensional electron gas, which may be relevant for the interpretation of experiments in thin films.

  1. Fermi wave vector for the partially spin-polarized composite-fermion Fermi sea

    Science.gov (United States)

    Balram, Ajit C.; Jain, J. K.

    2017-12-01

    The fully spin-polarized composite-fermion (CF) Fermi sea at the half-filled lowest Landau level has a Fermi wave vector kF*=√{4 π ρe } , where ρe is the density of electrons or composite fermions, supporting the notion that the interaction between composite fermions can be treated perturbatively. Away from ν =1 /2 , the area is seen to be consistent with kF*=√{4 π ρe } for ν 1 /2 , where ρh is the density of holes in the lowest Landau level. This result is consistent with particle-hole symmetry in the lowest Landau level. We investigate in this article the Fermi wave vector of the spin-singlet CF Fermi sea (CFFS) at ν =1 /2 , for which particle-hole symmetry is not a consideration. Using the microscopic CF theory, we find that for the spin-singlet CFFS the Fermi wave vectors for up- and down-spin CFFSs at ν =1 /2 are consistent with kF*↑,↓=√{4 π ρe↑,↓ } , where ρe↑=ρe↓=ρe/2 , which implies that the residual interactions between composite fermions do not cause a nonperturbative correction for spin-singlet CFFS either. Our results suggest the natural conjecture that for arbitrary spin polarization the CF Fermi wave vectors are given by kF*↑=√{4 π ρe↑ } and kF*↓=√{4 π ρe↓ } .

  2. Direct injection of spin-polarized carriers across YBa2Cu3O7−δ ...

    Indian Academy of Sciences (India)

    In summary, we have shown that the direct injection of spin-polarized carriers from LCMO into YBCO suppresses the critical current of the YBCO layer due to the breaking of the time reversal symmetry of the Cooper pairs. Further, our experiments show that when the ferromagnetic LCMO layer is in direct contact with YBCO, ...

  3. Spin-polarized structural, elastic, electronic and magnetic properties of half-metallic ferromagnetism in V-doped ZnSe

    Energy Technology Data Exchange (ETDEWEB)

    Monir, M. El Amine.; Baltache, H. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Ahmed, Waleed K. [ERU, Faculty of Engineering, United Arab Emirates University, Al Ain (United Arab Emirates); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Omran, S. Bin [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Seddik, T. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria)

    2015-01-15

    Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn{sub 1−x}V{sub x}Se (for x=0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGA+U approximation (where U is the Hubbard correlation terms) is employed to treat the “d” electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGA+U schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) due to Se(4p)–V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 µ{sub B} and the minor atomic magnetic moment on Zn and Se are generated. - Highlights: • Half metallicity origins by doping V in ZnSe. • PBE-GGA+U approximation is employed to treat the “d” electrons properly. • s(p)-d Exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) are due to Se(4p)-V(3d) hybridization.

  4. Calculations of Non-equilibrium Effects in Nano-conductors

    DEFF Research Database (Denmark)

    Christensen, Rasmus Bjerregaard

    : An adatom on a Ag(111)surface and a C60 molecule on a Cu(111) surface. The calculated photon yield is found to agree with experiments for photons with energies below the applied bias (hω tunneling spectroscopy (IETS) serves as a powerful tool for non-destructive characterization...... and armchair chirality, and related the IETS signal to the phononic band structure. For the spin-polarized zigzag GNRs the role of the spin-polarization is investigated, revealing IETSas an indirect measurement of spin-polarization. Further, the role of impurities is explored, revealing the possibility...

  5. Spin-polarized scanning tunneling microscopy and spectroscopy study of chromium on a Cr(001) surface.

    Science.gov (United States)

    Lagoute, J; Kawahara, S L; Chacon, C; Repain, V; Girard, Y; Rousset, S

    2011-02-02

    Several tens of chromium layers were deposited at 250 °C on a Cr(001) surface and investigated by spin-polarized scanning tunneling microscopy (SP-STM), Auger electron spectroscopy (AES) and scanning tunneling spectroscopy (STS). Chromium is found to grow with a mound-like morphology resulting from the stacking of several monolayers which do not uniformly cover the whole surface of the substrate. The terminal plane consists of an irregular array of Cr islands with lateral sizes smaller than 20 × 20 nm(2). Combined AES and STS measurements reveal the presence of a significant amount of segregants prior to and after deposition. A detailed investigation of the surface shows that it consists of two types of patches. Thanks to STS measurements, the two types of area have been identified as being either chromium pure or segregant rich. SP-STM experiments have evidenced that the antiferromagnetic layer coupling remains in the chromium mounds after deposition and is not significantly affected by the presence of the segregants.

  6. Spin-polarized scanning tunneling microscopy with quantitative insights into magnetic probes.

    Science.gov (United States)

    Phark, Soo-Hyon; Sander, Dirk

    2017-01-01

    Spin-polarized scanning tunneling microscopy and spectroscopy (spin-STM/S) have been successfully applied to magnetic characterizations of individual nanostructures. Spin-STM/S is often performed in magnetic fields of up to some Tesla, which may strongly influence the tip state. In spite of the pivotal role of the tip in spin-STM/S, the contribution of the tip to the differential conductance d I /d V signal in an external field has rarely been investigated in detail. In this review, an advanced analysis of spin-STM/S data measured on magnetic nanoislands, which relies on a quantitative magnetic characterization of tips, is discussed. Taking advantage of the uniaxial out-of-plane magnetic anisotropy of Co bilayer nanoisland on Cu(111), in-field spin-STM on this system has enabled a quantitative determination, and thereby, a categorization of the magnetic states of the tips. The resulting in-depth and conclusive analysis of magnetic characterization of the tip opens new venues for a clear-cut sub-nanometer scale spin ordering and spin-dependent electronic structure of the non-collinear magnetic state in bilayer high Fe nanoislands on Cu(111).

  7. Spin-polarized supercurrents for spintronics: a review of current progress.

    Science.gov (United States)

    Eschrig, Matthias

    2015-10-01

    During the past 15 years a new field has emerged, which combines superconductivity and spintronics, with the goal to pave a way for new types of devices for applications combining the virtues of both by offering the possibility of long-range spin-polarized supercurrents. Such supercurrents constitute a fruitful basis for the study of fundamental physics as they combine macroscopic quantum coherence with microscopic exchange interactions, spin selectivity, and spin transport. This report follows recent developments in the controlled creation of long-range equal-spin triplet supercurrents in ferromagnets and its contribution to spintronics. The mutual proximity-induced modification of order in superconductor-ferromagnet hybrid structures introduces in a natural way such evasive phenomena as triplet superconductivity, odd-frequency pairing, Fulde-Ferrell-Larkin-Ovchinnikov pairing, long-range equal-spin supercurrents, [Formula: see text]-Josephson junctions, as well as long-range magnetic proximity effects. All these effects were rather exotic before 2000, when improvements in nanofabrication and materials control allowed for a new quality of hybrid structures. Guided by pioneering theoretical studies, experimental progress evolved rapidly, and since 2010 triplet supercurrents are routinely produced and observed. We have entered a new stage of studying new phases of matter previously out of our reach, and of merging the hitherto disparate fields of superconductivity and spintronics to a new research direction: super-spintronics.

  8. Perfect switching of the spin polarization in a ferromagnetic gapless graphene/superconducting gapped graphene junction

    International Nuclear Information System (INIS)

    Soodchomshom, Bumned; Tang, I-Ming; Hoonsawat, Rassmidara

    2010-01-01

    With the fabrication of gapped graphene, interest in the tunneling spectroscopy in graphene-based FG/SG junctions in which one side consists of a gapless ferro-magnetic graphene (FG) and the other side, of a gapped superconducting graphene (SG) has arisen. The carriers in the gapless (gapped) graphene are 2D relativistic particles having an energy spectrum given by E=√(h 2 v F 2 k 2 +(mv F 2 ) 2 ) (where mv F 2 is the gap and v F is the Fermi velocity). The spin currents in this FG/SG junction are obtained within the framework of the extended Blonder-Tinkham-Klapwijk (BTK) formalism. The effects of the superconducting energy gap in SG, of the gap mv F 2 which opened in the superconducting graphene, of the exchange field in FG, of the spin-dependent specular Andreev reflection, of the effective Fermi energy (E FF ) of FG and of the bias voltage across the junction (V) are simulated. It is seen that by adjusting E FF or V, the spin polarization (defined as SP(%) = 100% x (G ↑ - G ↓ )/(G ↑ + G ↓ )) can be switched from a pure spin up (SP = +100%) state to pure spin down (SP = -100%) state.

  9. Electrically tunable dynamic nuclear spin polarization in GaAs quantum dots at zero magnetic field

    Science.gov (United States)

    Manca, M.; Wang, G.; Kuroda, T.; Shree, S.; Balocchi, A.; Renucci, P.; Marie, X.; Durnev, M. V.; Glazov, M. M.; Sakoda, K.; Mano, T.; Amand, T.; Urbaszek, B.

    2018-04-01

    In III-V semiconductor nano-structures, the electron and nuclear spin dynamics are strongly coupled. Both spin systems can be controlled optically. The nuclear spin dynamics are widely studied, but little is known about the initialization mechanisms. Here, we investigate optical pumping of carrier and nuclear spins in charge tunable GaAs dots grown on 111A substrates. We demonstrate dynamic nuclear polarization (DNP) at zero magnetic field in a single quantum dot for the positively charged exciton X+ state transition. We tune the DNP in both amplitude and sign by variation of an applied bias voltage Vg. Variation of ΔVg on the order of 100 mV changes the Overhauser splitting (nuclear spin polarization) from -30 μeV (-22%) to +10 μeV (+7%) although the X+ photoluminescence polarization does not change sign over this voltage range. This indicates that absorption in the structure and energy relaxation towards the X+ ground state might provide favourable scenarios for efficient electron-nuclear spin flip-flops, generating DNP during the first tens of ps of the X+ lifetime which is on the order of hundreds of ps. Voltage control of DNP is further confirmed in Hanle experiments.

  10. Effect of the anisotropy of the electron g-factor in spin polarization

    International Nuclear Information System (INIS)

    Miah, M. Idrish; Gray, E. MacA.

    2010-01-01

    Spin polarization in the presence of an external magnetic field and electric bias in quantum confined semiconductor structures has been studied by time- and polarization-resolved spectrometry. From measurements with angular variations of the magnetic field from the Voigt configuration (VC) it was found that both the frequency (Ω) and decay rate (β) of the oscillatory component of the polarization increase with variation of the angle from the VC. Their dependences are discussed based on the electron spin dephasing related to the spread of the electron g-factor (g e ) (i.e. unequal values of the longitudinal (g e|| ) and transverse (g e -perpendicular) components of g e ) and the exchange interaction between the electron and hole spins. It is demonstrated that the increase in Ω upon deviation of the magnetic field from the VC relates to the anisotropy of g e (g e|| and g e -perpendicular) resulting from the quantum confinement effect. However, the angular dependence on β is related to the residual exchange interaction between the electron spin and rapidly relaxing hole spin.

  11. a Spinning Polarizer and Spinning Analyzer Method for Visualizing the Isochromates in Conoscopic Interferometers

    Science.gov (United States)

    Olorunsola, Oluwatobi; Dada, Oluwaseye; Wang, Pengqian

    2013-09-01

    We have developed a spinning polarizer and spinning analyzer (SPSA) method to visualize the whole isochromatic fringes in conoscopic interferometers for the study of optically anisotropic materials. This simple method completely eliminates the broad and dark isogyre fringes appearing in a conventional conoscopic interferometer where a linear polarizer and a linear analyzer (LPLA) are used. Our method allows the direct visualization of the isochromates on the viewing screen by eyes in real time, without the need of additional optics or detectors other than those used in a conventional conoscopic interferometer, and no additional computation is required. This method works at any polarization state of the input light, and at any wavelength permitted by the polarizers. In the case of polychromatic illumination our method reveals the isochromates of all colors indiscriminatively, in comparison to the method of circular polarizer and circular analyzer (CPCA), which is considerably subject to spectrum modulation due to the dispersion in the retardation of the quarter-wave plates. The proposed method is demonstrated in a lithium niobate (LiNbO3) crystal driven by an external electric field.

  12. Spin-polarized transport through single-molecule magnet Mn6 complexes

    KAUST Repository

    Cremades, Eduard

    2013-01-01

    The coherent transport properties of a device, constructed by sandwiching a Mn6 single-molecule magnet between two gold surfaces, are studied theoretically by using the non-equilibrium Green\\'s function approach combined with density functional theory. Two spin states of such Mn6 complexes are explored, namely the ferromagnetically coupled configuration of the six MnIII cations, leading to the S = 12 ground state, and the low S = 4 spin state. For voltages up to 1 volt the S = 12 ground state shows a current one order of magnitude larger than that of the S = 4 state. Furthermore this is almost completely spin-polarized, since the Mn6 frontier molecular orbitals for S = 12 belong to the same spin manifold. As such the high-anisotropy Mn6 molecule appears as a promising candidate for implementing, at the single molecular level, both spin-switches and low-temperature spin-valves. © 2013 The Royal Society of Chemistry.

  13. Laser-driven source of spin-polarized atomic hydrogen and deuterium

    International Nuclear Information System (INIS)

    Poelker, M.

    1995-01-01

    A laser-driven source of spin-polarized hydrogen (H) and deuterium (D) that relies on the technique of optical pumping spin exchange has been constructed. In this source, H or D atoms and potassium atoms flow continuously through a drifilm-coated spin-exchange cell where potassium atoms are optically pumped with circularly-polarized laser light in a high magnetic field. The H or D atoms become polarized through spin-exchange collisions with polarized potassium atoms. High electron polarization (∼80%) has been measured for H and D atoms at flow rates ∼2x10 17 atoms/s. Lower polarization values are measured for flow rates exceeding 1x10 18 atoms/s. In this paper, we describe the performance of the laser-driven source as a function of H and D atomic flow rate, magnetic field strength, alkali density and pump-laser power. Polarization measurements as a function of flow rate and magnetic field suggest that, despite a high magnetic field, atoms within the optical-pumping spin-exchange apparatus evolve to spin-temperature equilibrium which results in direct polarization of the H and D nuclei. (orig.)

  14. Effect of the anisotropy of the electron g-factor in spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M. Idrish, E-mail: m.miah@griffith.edu.au [Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong, Chittagong 4331 (Bangladesh); Gray, E. MacA. [Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia)

    2010-02-15

    Spin polarization in the presence of an external magnetic field and electric bias in quantum confined semiconductor structures has been studied by time- and polarization-resolved spectrometry. From measurements with angular variations of the magnetic field from the Voigt configuration (VC) it was found that both the frequency ({Omega}) and decay rate ({beta}) of the oscillatory component of the polarization increase with variation of the angle from the VC. Their dependences are discussed based on the electron spin dephasing related to the spread of the electron g-factor (g{sub e}) (i.e. unequal values of the longitudinal (g{sub e||}) and transverse (g{sub e}-perpendicular) components of g{sub e}) and the exchange interaction between the electron and hole spins. It is demonstrated that the increase in {Omega} upon deviation of the magnetic field from the VC relates to the anisotropy of g{sub e} (g{sub e||} and g{sub e}-perpendicular) resulting from the quantum confinement effect. However, the angular dependence on {beta} is related to the residual exchange interaction between the electron spin and rapidly relaxing hole spin.

  15. Domain Wall Dynamics Driven by a Localized Injection of a Spin-Polarized Current

    Science.gov (United States)

    Finocchio, Giovanni; Maugeri, Natale; Torres, Luis; Azzerboni, Bruno

    2010-06-01

    This paper introduces an oscillator scheme based on the oscillations of magnetic domain walls due to spin-polarized currents, where the current is injected perpendicular to the sample plane in a localized part of a nanowire. Depending on the geometrical and physical characteristic of the system, we identify two different dynamical regimes (auto-oscillations) when an out-of-plane external field is applied. The first regime is characterized by nucleation of domain walls (DWs) below the current injection site and the propagation of those up to the end of the nanowire, we also found an oscillation frequency larger than 5GHz with a linear dependence on the applied current density. This simple system can be used as a tuneable steady-state domain wall oscillator. In the second dynamical regime, we observe the nucleation of two DWs which propagate back and forth in the nanowire with a sub-GHz oscillation frequency. The micromagnetic spectral mapping technique shows the spatial distribution of the output power is localized symmetrically in the nanowire. We suggest that this configuration can be used as micromagnetic transformer to decouple electrically two different circuits.

  16. Joule heating and spin-transfer torque investigated on the atomic scale using a spin-polarized scanning tunneling microscope.

    Science.gov (United States)

    Krause, S; Herzog, G; Schlenhoff, A; Sonntag, A; Wiesendanger, R

    2011-10-28

    The influence of a high spin-polarized tunnel current onto the switching behavior of a superparamagnetic nanoisland on a nonmagnetic substrate is investigated by means of spin-polarized scanning tunneling microscopy. A detailed lifetime analysis allows for a quantification of the effective temperature rise of the nanoisland and the modification of the activation energy barrier for magnetization reversal, thereby using the nanoisland as a local thermometer and spin-transfer torque analyzer. Both the Joule heating and spin-transfer torque are found to scale linearly with the tunnel current. The results are compared to experiments performed on lithographically fabricated magneto-tunnel junctions, revealing a very high spin-transfer torque switching efficiency in our experiments.

  17. Dresselhaus spin-orbit coupling induced spin-polarization and resonance-split in n-well semiconductor superlattices

    International Nuclear Information System (INIS)

    Ye Chengzhi; Xue Rui; Nie, Y.-H.; Liang, J.-Q.

    2009-01-01

    Using the transfer matrix method, we investigate the electron transmission over multiple-well semiconductor superlattices with Dresselhaus spin-orbit coupling in the potential-well regions. The superlattice structure enhances the effect of spin polarization in the transmission spectrum. The minibands of multiple-well superlattices for electrons with different spin can be completely separated at the low incident energy, leading to the 100% spin polarization in a broad energy windows, which may be an effective scheme for realizing spin filtering. Moreover, for the transmission over n-quantum-well, it is observed that the resonance peaks in the minibands split into n-folds or (n-1)-folds depending on the well-width and barrier-thickness, which is different from the case of tunneling through n-barrier structure

  18. Thermally induced pure and spin polarized currents in a zigzag silicene nanoribbon based FM/normal/AFM junction

    Science.gov (United States)

    Ghanbari, Atousa; Esmaeilzadeh, Mahdi; Pournaghavi, Nezhat

    2018-01-01

    We study thermally induced spin resolved current in a zigzag silicene nanoribbon when the left and right leads are respectively affected by ferromagnetic (FM) and anti-ferromagnetic (AFM) exchange fields (FM/normal/AFM junction). We show that pure spin current is generated due to the leads temperature difference and the junction can work as a spin Seebeck diode. The pure spin current can be easily controlled by a perpendicular electric field and the junction, in this case, can work as a spin current switch. In addition, we study the effect of a single vacancy and show that the vacancy can slightly destroy the pure spin current property which leads to induce a weak spin polarized current. In the presence of both vacancy and electric field, current with high and tunable spin polarization can be achieved.

  19. Period-doubling bifurcation cascade observed in a ferromagnetic nanoparticle under the action of a spin-polarized current

    Energy Technology Data Exchange (ETDEWEB)

    Horley, Paul P., E-mail: paul.horley@cimav.edu.mx [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Kushnir, Mykola Ya. [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine); Morales-Meza, Mishel [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Sukhov, Alexander [Institut für Physik, Martin-Luther Universität Halle-Wittenberg, 06120 Halle (Saale) (Germany); Rusyn, Volodymyr [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine)

    2016-04-01

    We report on complex magnetization dynamics in a forced spin valve oscillator subjected to a varying magnetic field and a constant spin-polarized current. The transition from periodic to chaotic magnetic motion was illustrated with bifurcation diagrams and Hausdorff dimension – the methods developed for dissipative self-organizing systems. It was shown that bifurcation cascades can be obtained either by tuning the injected spin-polarized current or by changing the magnitude of applied magnetic field. The order–chaos transition in magnetization dynamics can be also directly observed from the hysteresis curves. The resulting complex oscillations are useful for development of spin-valve devices operating in harmonic and chaotic modes.

  20. Spin-polarized quasi-one-dimensional state with finite band gap on the Bi/InSb(001) surface

    Science.gov (United States)

    Kishi, J.; Ohtsubo, Y.; Nakamura, T.; Yaji, K.; Harasawa, A.; Komori, F.; Shin, S.; Rault, J. E.; Le Fèvre, P.; Bertran, F.; Taleb-Ibrahimi, A.; Nurmamat, M.; Yamane, H.; Ideta, S.; Tanaka, K.; Kimura, S.

    2017-11-01

    One-dimensional (1D) electronic states were discovered on the 1D surface atomic structure of Bi fabricated on semiconductor InSb(001) substrates by angle-resolved photoelectron spectroscopy (ARPES). The 1D state showed steep, Dirac-cone-like dispersion along the 1D atomic structure with a finite direct band gap opening as large as 150 meV. Moreover, spin-resolved ARPES revealed the spin polarization of the 1D unoccupied states as well as that of the occupied states, the orientation of which inverted depending on the wave-vector direction parallel to the 1D array on the surface. These results reveal that a spin-polarized quasi-1D carrier was realized on the surface of 1D Bi with highly efficient backscattering suppression, showing promise for use in future spintronics and energy-saving devices.

  1. Influence of intrinsic spin-flip processes on spin-polarized transport through quantum dots in the cotunneling regime

    International Nuclear Information System (INIS)

    Weymann, I.; Barnas, J.

    2006-01-01

    The influence of intrinsic spin relaxation on spin-polarized cotunneling through quantum dots coupled to ferromagnetic leads is analyzed theoretically. It is shown that the zero bias anomaly, which occurs due to the interplay of single-barrier and double-barrier cotunneling processes, becomes suppressed by spin relaxation processes on the dot. Diode-like features of the transport characteristics in the cotunneling regime have been found in asymmetrical systems. These features are also suppressed by the spin relaxation processes

  2. Monte Carlo studies of thermalization of electron-hole pairs in spin-polarized degenerate electron gas in monolayer graphene

    Science.gov (United States)

    Borowik, Piotr; Thobel, Jean-Luc; Adamowicz, Leszek

    2018-02-01

    Monte Carlo method is applied to the study of relaxation of excited electron-hole (e-h) pairs in graphene. The presence of background of spin-polarized electrons, with high density imposing degeneracy conditions, is assumed. To such system, a number of e-h pairs with spin polarization parallel or antiparallel to the background is injected. Two stages of relaxation: thermalization and cooling are clearly distinguished when average particles energy and its standard deviation σ _E are examined. At the very beginning of thermalization phase, holes loose energy to electrons, and after this process is substantially completed, particle distributions reorganize to take a Fermi-Dirac shape. To describe the evolution of and σ _E during thermalization, we define characteristic times τ _ {th} and values at the end of thermalization E_ {th} and σ _ {th}. The dependence of these parameters on various conditions, such as temperature and background density, is presented. It is shown that among the considered parameters, only the standard deviation of electrons energy allows to distinguish between different cases of relative spin polarizations of background and excited electrons.

  3. Insight into electronic, mechanical and transport properties of quaternary CoVTiAl: Spin-polarized DFT + U approach

    Energy Technology Data Exchange (ETDEWEB)

    Yousuf, Saleem, E-mail: nengroosaleem17@gmail.com; Gupta, D.C., E-mail: sosfizix@gmail.com

    2017-07-15

    Highlights: • 100% spin-polarized material important for the application in spintronics. • It is ferromagnetic and ductile in nature. • Shows semiconducting behavior with a band gap of 1.06 eV. • Possibly efficient high temperature thermoelectric material. - Abstract: We present a preliminary investigation of band structure and thermoelectric properties of new quaternary CoVTiAl Heusler alloy. Structural, magnetic property and 100% spin polarization of equiatomic CoVTiAl predicts ferromagnetic stable ground state. Band profile outlines the indirect semiconducting behavior in spin down channel with band gap of 1.06 eV, and the magnetic moment of 3 µ{sub B} in accordance with Slater-Pauling rule. To evaluate the accuracy of different approximations in predicting thermoelectric properties, the comparison with available experimental data is made which shows fair agreement for the transport coefficients. The high temperature (800 K) positive Seebeck coefficient of 73.71 µV/K describes the p-type character of the material with high efficiency due to highly influential semiconducting behavior around the Fermi level. Considering the combination of 100% spin-polarization, high Seebeck coefficient and large figure of merit, ferromagnetic semiconducting CoVTiAl may prove as a potential candidate for high temperature thermoelectrics and an ideal spin source material for spintronic applications.

  4. Fabrication of highly spin-polarized Co2FeAl0.5Si0.5 thin-films

    Directory of Open Access Journals (Sweden)

    M. Vahidi

    2014-04-01

    Full Text Available Ferromagnetic Heusler Co2FeAl0.5Si0.5 epitaxial thin-films have been fabricated in the L21 structure with saturation magnetizations over 1200 emu/cm3. Andreev reflection measurements show that the spin polarization is as high as 80% in samples sputtered on unheated MgO (100 substrates and annealed at high temperatures. However, the spin polarization is considerably smaller in samples deposited on heated substrates.

  5. NMR investigations of surfaces and interfaces using spin-polarized xenon

    Energy Technology Data Exchange (ETDEWEB)

    Gaede, Holly Caroline [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1995-07-01

    129Xe NMR is potentially useful for the investigation of material surfaces, but has been limited to high surface area samples in which sufficient xenon can be loaded to achieve acceptable signal to noise ratios. In Chapter 2 conventional 129Xe NMR is used to study a high surface area polymer, a catalyst, and a confined liquid crystal to determine the topology of these systems. Further information about the spatial proximity of different sites of the catalyst and liquid crystal systems is determined through two dimensional exchange NMR in Chapter 3. Lower surface area systems may be investigated with spin-polarized xenon, which may be achieved through optical pumping and spin exchange. Optically polarized xenon can be up to 105times more sensitive than thermally polarized xenon. In Chapter 4 highly polarized xenon is used to examine the surface of poly(acrylonitrile) and the formation of xenon clathrate hydrates. An attractive use of polarized xenon is as a magnetization source in cross polarization experiments. Cross polarization from adsorbed polarized xenon may allow detection of surface nuclei with drastic enhancements. A non-selective low field thermal mixing technique is used to enhance the 13C signal of CO2 of xenon occluded in solid CO2 by a factor of 200. High-field cross polarization from xenon to proton on the surface of high surface area polymers has enabled signal enhancements of ~1,000. These studies, together with investigations of the efficiency of the cross polarization process from polarized xenon, are discussed in Chapter 5. Another use of polarized xenon is as an imaging contrast agent in systems that are not compatible with traditional contrast agents. The resolution attainable with this method is determined through images of structured phantoms in Chapter 6.

  6. Production of highly spin-polarized atomic hydrogen and deuterium by spin-exchange

    International Nuclear Information System (INIS)

    Redsun, S.G.

    1990-01-01

    The first part of this work is a study of the production of highly spin-polarized atomic hydrogen and deuterium by spin-exchange optical pumping. A tunable ring dye laser is used to polarize rubidium atoms by optical pumping. The cell containing the rubidium vapor is coated with paraffin in order to reduce spin relaxation due to wall collisions. Hydrogen gas is dissociated in an inductive discharge and flows continuously through the cell, in which the hydrogen atoms are polarized by spin-exchange collisions with the polarized rubidium atoms. The hydrogen polarization is determined by a combination of fluorescence monitoring and magnetic resonance spectroscopy. Atomic hydrogen polarization as high as 2 z > H = 0.72(6) has been observed, which is the highest degree of polarization yet produced by this method. However, the polarization may be limited to this value due to the depolarization of the rubidium by radiation trapping. The spin-relaxation rate of atomic hydrogen on a paraffin-coated cell is also measured for the first time, and corresponds to about 3,800 wall bounces before electron-spin randomization. The second part of this work is a theoretical analysis of the problem of radiation trapping in a dense optically pumped alkali vapor. A Monte Carlo routine is used to simulate the trajectories of multiply scattered photons. The average spin angular momentum transfer from the photons to the vapor is used to determine the equilibrium polarization of the vapor as a function of the alkali density and the frequency of the pumping light

  7. Development, construction and characterization of a variable repetitive spin-polarized electron gun with an inverted-geometry insulator

    International Nuclear Information System (INIS)

    Espig, Martin

    2016-02-01

    Within the scope of this thesis a pulsed source of spin polarized electrons Photo-CATCH was designed, constructed, characterized and has been put into operation. This source is based on the photoemission of spin-polarized electrons from GaAs-photocathodes. Both the design of the electron gun, consisting of an ultra-high vacuum chamber and an electrode with Pierce geometry, as well as the properties of the electron beam have been simulated with CST Studio. Results were a maximum electric field of (0.064±0.001) MV/m/kV on the electrode surface and a beam emittance as a function of the radius of the laser spot on the photocathode of element of n,x =(1.7478(4).10 -4 .(r)/(μm)+2.8(18).10 -5 ) mm mrad at a beam current of 100 μA. Currently Photo-CATCH provides electron beams with an energy of 60 keV, which can be expanded up to 100 keV by upgrading the high-voltage power supply. The electron gun has an inverted-geometry insulator to ensure a compact design of the ultra-high vacuum chamber and a maximum person- and machine-safety from sparkovers. Since the properties of the laser light directly affect the properties of the generated electron beam a pulsed semiconductor laser system has been specially developed and built for Photo-CATCH. This is characterized by a high variability of its operating parameters, in particular its wavelength and repetition rate, in order to fulfill the broad variety of requirements of various nuclear physics experiments. By selecting the wavelength of the used laser diode highly polarized or high-current electron beams can be generated from GaAs-photocathodes. The time profile of the laser has direct influence to the longitudinal profile of the electron bunch. Through the radiofrequency modulation of the pumping current of the impedance-matched semiconductor laser system, consisting of a DC power source and an electrical pulse generator with 881 ps broad pump pulses, Lorentz shaped laser pulses with a minimum FWHM of (43.8±1.2) ps at a

  8. Dimensionality effects on spin-polarized quantum beats in ferromagnetic hosts with a pair of side-coupled impurities

    Energy Technology Data Exchange (ETDEWEB)

    Guessi, L.H.; Leandro, S.C.; Seridonio, A.C.; Siqueira, E.C. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Ilha Solteira, SP (Brazil). Dept. de Fisico Quimica; Souza, F.M.; Vernek, E. [Universidade Federal de Uberlandia (UFU), MG (Brazil). Inst. de Fisica; Yoshida, M. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Rio Claro, SP (Brazil); Figueira, M.S. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Fisica

    2012-07-01

    Full text: In this work, we report a theoretical description of the differential conductance in the low bias regime, for a normal scanning tunneling microscope (STM) probe in the presence of ferromagnetic (FM) hosts with impurities. The hosts are treated as a spin-polarized electron gas hybridized to a pair of side-coupled impurities. Two setups of different dimensionalities are considered, a quantum wire (QW) and a metallic surface (MS). In order to deal with the non-interacting and the Coulomb blockade regimes of these systems, the analysis is done in the framework of the two-impurity Anderson model (TIAM) in combination with the equation of motion (EOM) approach for the Hamiltonian Green functions (GFs). The Fano effect appears in such setups, due to the quantum interference between the transport channels composed by the spin-polarized conduction bands and the electron tunneling into (or out of) the impurities. Thus the conductance of the STM reveals as a function of the probe position, a Fano interference strong dependent on the host dimensionality. It leads to the emergence of spin-polarized quantum beats in the Friedel oscillations for the conductance signal, which are uniform in the QW system in opposite to those found in the MS case, characterized by a long-range damped behavior. We remark that, the energy levels of the impurities and the Coulomb repulsion, modulate these beats. As a result, they establish a scenario where the interplay between the Coulomb blockade and the ferromagnetism of a metallic environment, can be useful for future quantum computation devices. (author)

  9. Experimental verification of the rotational type of chiral spin spiral structures by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Haze, Masahiro; Yoshida, Yasuo; Hasegawa, Yukio

    2017-10-16

    We report on experimental verification of the rotational type of chiral spin spirals in Mn thin films on a W(110) substrate using spin-polarized scanning tunneling microscopy (SP-STM) with a double-axis superconducting vector magnet. From SP-STM images using Fe-coated W tips magnetized to the out-of-plane and [001] directions, we found that both Mn mono- and double-layers exhibit cycloidal rotation whose spins rotate in the planes normal to the propagating directions. Our results agree with the theoretical prediction based on the symmetry of the system, supporting that the magnetic structures are driven by the interfacial Dzyaloshinskii-Moriya interaction.

  10. Spin-polarized scanning tunneling spectroscopy of self-organized nanoscale Co islands on Au(111) surfaces.

    Science.gov (United States)

    Schouteden, K; Muzychenko, D A; Van Haesendonck, C

    2008-07-01

    Magnetic monolayer and bilayer Co islands of only a few nanometer in size were grown by atomic deposition on atomically flat Au(111) films. The islands were studied in situ by scanning tunneling microscopy (STM) and spectroscopy at low temperatures. Spin-resolved tunneling spectroscopy, using an STM tip with a magnetic coating, revealed that the Co islands exhibit a net magnetization perpendicular to the substrate surface due to the presence of spin-polarized d-states. A random distribution of islands with either upward or downward pointing magnetization was observed, without any specific correlation of magnetization orientation with island size or island height.

  11. First-principles study of spin-polarized electronic band structures in ferromagnetic Zn1-xTMxS (TM = Fe, Co and Ni)

    KAUST Repository

    Saeed, Yasir

    2010-10-01

    We report a first-principles study of structural, electronic and magnetic properties of crystalline alloys Zn1-xTMxS (TM = Fe, Co and Ni) at x = 0.25. Structural properties are computed from the total ground state energy convergence and it is found that the cohesive energies of Zn 1-xTMxS are greater than that of zincblende ZnS. We also study the spin-polarized electronic band structures, total and partial density of states and the effect of TM 3d states. Our results exhibit that Zn 0.75Fe0.25S, Zn0.75Co0.25S and Zn0.75Ni0.25S are half-metallic ferromagnetic with a magnetic moment of 4μB, 3μB and 2μB, respectively. Furthermore, we calculate the TM 3d spin-exchange-splitting energies Δx (d), Δx (x-d), exchange constants N0α and N0β, crystal field splitting (ΔEcrystEt2g-Eeg), and find that p-d hybridization reduces the local magnetic moment of TM from its free space charge value. Moreover, robustness of Zn1-xTMxS with respect to the variation of lattice constants is also discussed. © 2010 Elsevier B.V. All rights reserved.

  12. Robustness Metrics: How Are They Calculated, When Should They Be Used and Why Do They Give Different Results?

    Science.gov (United States)

    McPhail, C.; Maier, H. R.; Kwakkel, J. H.; Giuliani, M.; Castelletti, A.; Westra, S.

    2018-02-01

    Robustness is being used increasingly for decision analysis in relation to deep uncertainty and many metrics have been proposed for its quantification. Recent studies have shown that the application of different robustness metrics can result in different rankings of decision alternatives, but there has been little discussion of what potential causes for this might be. To shed some light on this issue, we present a unifying framework for the calculation of robustness metrics, which assists with understanding how robustness metrics work, when they should be used, and why they sometimes disagree. The framework categorizes the suitability of metrics to a decision-maker based on (1) the decision-context (i.e., the suitability of using absolute performance or regret), (2) the decision-maker's preferred level of risk aversion, and (3) the decision-maker's preference toward maximizing performance, minimizing variance, or some higher-order moment. This article also introduces a conceptual framework describing when relative robustness values of decision alternatives obtained using different metrics are likely to agree and disagree. This is used as a measure of how "stable" the ranking of decision alternatives is when determined using different robustness metrics. The framework is tested on three case studies, including water supply augmentation in Adelaide, Australia, the operation of a multipurpose regulated lake in Italy, and flood protection for a hypothetical river based on a reach of the river Rhine in the Netherlands. The proposed conceptual framework is confirmed by the case study results, providing insight into the reasons for disagreements between rankings obtained using different robustness metrics.

  13. Simple and efficient method of spin-polarizing a metastable helium beam by diode laser optical pumping

    International Nuclear Information System (INIS)

    Granitza, B.; Salvietti, M.; Torello, E.; Mattera, L.; Sasso, A.

    1995-01-01

    Diode laser optical pumping to produce a highly spin-polarized metastable He beam to be used in a spin-polarized metastable atom deexcitation spectroscopy experiment on magnetized surfaces is described. Efficient pumping of the beam is performed by means of an SDL-6702 distributed Bragg reflector diode laser which yields 50 mW of output power in a single longitudinal mode at 1083 nm, the resonance wavelength for the 2 3 S→2 3 P 0,1,2 (D 0 , D 1 , and D 2 ) transitions of He*. The light is circularly polarized by a quarter-wave plate, allowing easy change of the sense of atomic polarization. The laser frequency can be locked to the atomic transition for several hours by phase-sensitive detection of the saturated absorption signal in a He discharge cell. Any of the three transitions of the triplet system can be pumped with the laser but the maximum level of atomic polarization of 98.5% is found pumping the D 2 line. copyright 1995 American Institute of Physics

  14. Oliver E. Buckley Prize Talk: Spin polarized tunneling and tunnel magnetoresistance -- Learning from the past and moving forward

    Science.gov (United States)

    Moodera, Jagadeesh

    2009-03-01

    Electron tunneling phenomenon has contributed enormously to our understanding of various branches of physics over the years. The technique of spin polarized tunneling (SPT), sensing the spin polarization of tunneling electrons using a superconducting spin detector, discovered by Meservey and Tedrow in the early seventies has been successfully utilized over the years to understand many aspects of magnetism and superconductivity. Electrical spin injection/detection in a semiconductor is strongly believed to succeed through such an approach. The successful observation of a large change in tunnel current in magnetic tunnel junctions (MTJ) in the mid nineties has brought extreme activity in this field -- both from fundamental study as well as extensive application in mind (as sensors, nonvolatile memory devices, logic elements etc). From the early history of this field that led to the discovery of room temperature TMR effect to the observation of many novel phenomena to the exciting recent work on spin filtering, spin transport in semiconductors to toggling of the superconducting state with spin current will be highlighted and reviewed. Work done in collaboration with Drs. Meservey and Tedrow, PhD students, postdoctorals, as well as high school students and undergraduates. NSF, ONR, DARPA and KIST-MIT project funds supported the research over the years.

  15. New-type spin polarized electron source and its applications; Atarashii spin henkyoku denshi sengen to sono oyo

    Energy Technology Data Exchange (ETDEWEB)

    Saka, T.; Kato, T. [Daido Steel Co. Ltd., Nagoya (Japan); Nakanishi, T.; Okumi, S. [Nagoya University, Nagoya (Japan); Horinaka, H. [Osaka Prefectural University, Osaka (Japan). College of Engineering

    1998-08-20

    This paper reveals that using distorted thin GaAs film can realize high polarization in spin polarized electron ray, and introduces properties of the developed ray source. The paper also touches on the application thereof to property physics. Realization of the high spin polarization is based on use of the `optical polarization method`. With this method, electrons in specific spin state are excited into a conduction band by utilizing the selection law used when valency electrons of zincblende type crystal such as GaAs absorb circular polarization. These electrons are taken out into vacuum and used as polarized electron beams. In order to realize uniformly distorted GaAs film, a method was discussed, with which the thin GaAs films are grown on substrates with different lattice constants, and the films are distorted by means of lattice mismatch. GaAs(1-x)Px was used for the substrates. GaAs(1-x)Px has the lattice constant decrease as the P`s mixed crystal ratio `x` increases. If a thin GaAs film is grown on this substrate, it is possible to obtain GaAs which is subjected to compression stress in the direction parallel with the growing surface, and tensile stress in the vertical direction. 13 refs., 5 figs., 1 tab.

  16. Spin-polarized transport in manganite-based magnetic nano structures

    International Nuclear Information System (INIS)

    Granada, Mara

    2007-01-01

    Giant magnetoresistance (G M R) and tunnel magnetoresistance are spin polarized transport phenomena which are observed in magnetic multilayers.They consist in a large variation of the electrical resistivity of the system depending on whether the magnetizations of the magnetic layers are aligned parallel or anti-parallel to each other. In order to be able to align the magnetic layers by means of an external magnetic field, they must not be strongly ferromagnetically coupled.The extrinsic magnetoresistance effects in magnetic multilayers, either G M R in the case of a metallic spacer, or T M R in the case of an insulating spacer, are observed at low magnetic fields, which makes these phenomena interesting for technological applications.We studied the possibility of using the ferromagnetic manganite La 0 ,75Sr 0 ,25MnO 3 (L S M O) in magneto resistive devices, with different materials as a spacer layer.As the main result of this work, we report G M R and T M R measurements in L S M O/LaNiO 3 /L S M O and L S M O/CaMnO 3 /L S M O tri layers, respectively, observed for the first time in these systems.This work included the deposition of films and multilayers by sputtering, the structural characterization of the samples and the study of their magnetic and electric transport properties.Our main interest was the study of G M R in L S M O/LaNiO 3 /L S M O tri layers.It was necessary to firstly characterize the magnetic coupling of L S M O layers through the L N O spacer. After that, we performed electric transport measurements with the current in the plane of the samples.We measured a G M R contribution of ∼ 0,55 % at T = 83 K.We designed a procedure for patterning the samples by e-beam lithography for electric transport measurements with the current perpendicular to the plane. We also performed the study of L S M O/CaMnO 3 /L S M O tri layers with an insulating spacer.We studied the magnetic coupling, as in the previous case.Then we fabricated a tunnel junction for

  17. Anisotropic magnetoresistance and spin polarization of La0.7Sr0.3MnO3/SrTiO3 superlattices

    International Nuclear Information System (INIS)

    Wang, L.M.; Guo, C.-C.

    2005-01-01

    The crystalline structure, anisotropic magnetoresistance (AMR), and magnetization of La 0.7 Sr 0.3 MnO 3 /SrTiO 3 (LSMO/STO) superlattices grown by a rf sputtering system are systematically analyzed to study the spin polarization of manganite at interfaces. The presence of positive low-temperature AMR in LSMO/STO superlattices implies that two bands of majority and minority character contribute to the transport properties, leading to a reduced spin polarization. Furthermore, the magnetization of superlattices follows the T 3/2 law and decays more quickly as the thickness ratio d STO /d LSMO increases, corresponding to a reduced exchange coupling. The results clearly show that the spin polarization is strongly correlated with the influence of interface-induced strain on the structure

  18. Fabrication of highly spin-polarized Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} thin-films

    Energy Technology Data Exchange (ETDEWEB)

    Vahidi, M.; Zhang, S. K.; Yu, L.; Huang, M.; Newman, N., E-mail: Nathan.Newman@asu.edu [School of Materials, Arizona State University, Tempe, Arizona 85287-8706 (United States); Gifford, J. A.; Chen, T. Y. [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Krishnamurthy, S.; Yu, Z. G. [SRI International, 301-64, Menlo Park, California 94025 (United States); Youngbull, C. [The Biodesign Institute, Arizona State University, Tempe, Arizona 85287 (United States)

    2014-04-01

    Ferromagnetic Heusler Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} epitaxial thin-films have been fabricated in the L2{sub 1} structure with saturation magnetizations over 1200 emu/cm{sup 3}. Andreev reflection measurements show that the spin polarization is as high as 80% in samples sputtered on unheated MgO (100) substrates and annealed at high temperatures. However, the spin polarization is considerably smaller in samples deposited on heated substrates.

  19. Development of a LabVIEW-based surface with innovative controls for the control system of the spin-polarized electron test source Photo-CATCH

    Energy Technology Data Exchange (ETDEWEB)

    Roesch, Heidi Ayse; Enders, Joachim; Espig, Martin; Fritzsche, Yuliya; Wagner, Markus [TU Darmstadt, Institut fuer Kernphysik (Germany)

    2016-07-01

    Operations of the spin-polarized electron source of the S-DALINAC will be supported by a photo-cathode activation, test and cleaning system, Photo-CATCH. Besides cathode-performance studies, this teststand produces spin-polarized electron bunches from a GaAs photo-cathode that are then transported, manipulated, and characterized by devices in a low-energy beam line. To set and monitor the various components of the beamline, a control system was developed, based on the EPICS framework. As interfaces, LabVIEW was used in combination with a gamepad as a controlling device.

  20. The tunneling magnetoresistance and spin-polarized optoelectronic properties of graphyne-based molecular magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Yang, Zhi; Ouyang, Bin; Lan, Guoqing; Xu, Li-Chun; Liu, Ruiping; Liu, Xuguang

    2017-01-01

    Using density functional theory and the non-equilibrium Green’s function method, we investigate the spin-dependent transport and optoelectronic properties of the graphyne-based molecular magnetic tunnel junctions (MMTJs). We find that these MMTJs exhibit an outstanding tunneling magnetoresistance (TMR) effect. The TMR value is as high as 10 6 %. When the magnetization directions of two electrodes are antiparallel under positive or negative bias voltages, two kinds of pure spin currents can be obtained in the systems. Furthermore, under the irradiation of infrared, visible or ultraviolet light, spin-polarized photocurrents can be generated in the MMTJs, but the corresponding microscopic mechanisms are different. More importantly, if the magnetization directions of two electrodes are antiparallel, the photocurrents with different spins are spatially separated, appearing at different electrodes. This phenomenon provides a new way to simultaneously generate two spin currents. (paper)

  1. Spin-polarized charge transport in HgTe/CdTe quantum well topological insulator under a ferromagnetic metal strip

    Science.gov (United States)

    Wu, Zhenhua; Luo, Kun; Yu, Jiahan; Wu, Xiaobo; Lin, Liangzhong

    2018-02-01

    Electron tunneling through a single magnetic barrier in a HgTe topological insulator has been theoretically investigated. We find that the perpendicular magnetic field would not lead to spin-flip of the edge states due to the conservation of the angular moment. By tuning the magnetic field and the Fermi energy, the edge channels can be transited from switch-on states to switch-off states and the current from unpolarized states can be filtered to fully spin polarized states. These features offer us an efficient way to control charge/spin transport in a HgTe/CdTe quantum well, and pave a way to construct the nanoelectronic devices utilizing the topological edge states.

  2. Effects of Be acceptors on the spin polarization of carriers in p-i-n resonant tunneling diodes

    Energy Technology Data Exchange (ETDEWEB)

    Awan, I. T.; Galvão Gobato, Y. [Departamento de Física, Universidade Federal de São Carlos (UFSCAR) 13560-905, São Carlos, SP (Brazil); Galeti, H. V. A. [Departamento de Engenharia Elétrica, Universidade Federal de São Carlos 13560-905, São Carlos, SP (Brazil); Brasil, M. J. S. P. [Institute of Physics Gleb Wataghin, UNICAMP, Campinas (Brazil); Taylor, D.; Henini, M. [School of Physics and Astronomy, Nottingham Nanotechnology and Nanoscience Centre, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2014-08-07

    In this paper, we have investigated the effect of Be acceptors on the electroluminescence and the spin polarization in GaAs/AlAs p-i-n resonant tunneling diodes. The quantum well emission comprise two main lines separated by ∼20 meV attributed to excitonic and Be-related transitions, which intensities show remarkably abrupt variations at critical voltages, particularly at the electron resonant peak where it shows a high-frequency bistability. The circular-polarization degree of the quantum-well electroluminescence also shows strong and abrupt variations at the critical bias voltages and it attains relatively large values (of ∼−75% at 15 T). These effects may be explored to design novel devices for spintronic applications such as a high-frequency spin-oscillators.

  3. Self-energy-part resummed quark and gluon propagators in a spin-polarized quark matter and generalized Boltzmann equations

    International Nuclear Information System (INIS)

    Niegawa, A.

    2003-01-01

    We construct perturbative frameworks for studying nonequilibrium spin-polarized quark matter. We employ the closed-time-path formalism and use the gradient approximation in derivative expansion. After constructing self-energy-part resummed quark and gluon propagators, we formulate two kinds of mutually equivalent perturbative frameworks: The first one is formulated on the basis of the initial-particle distribution function, and the second one is formulated on the basis of a 'physical' particle distribution function. In the course of the construction of the second framework, the generalized Boltzmann equations and their relatives directly come out, which describe the evolution of the system. The frameworks are relevant to the study of a magnetic character of quark matter, e.g., possible quark stars

  4. Giving feedback.

    Science.gov (United States)

    Thomas, Jane DeLima; Arnold, Robert M

    2011-02-01

    Giving feedback is a core element of medical education, one that is gaining attention but with a thin evidence base to guide medical educators. This review provides a definition of feedback and its purpose, selectively reviews the literature regarding educators' and learners' attitudes toward feedback, and provides an algorithm for giving feedback. The authors discuss the parallels between giving feedback and breaking bad news, emphasizing the importance of titrating the amount of information given, attending to affect, and making a plan for next steps. Special considerations for giving feedback in palliative care are highlighted, including the effect of heightened emotion in the clinical encounter and the difficulties of giving feedback about communication skills.

  5. 2D Electron Gas with 100% Spin-Polarization in the (LaMnO3)2/(SrTiO3)2 Superlattice under Uniaxial Strain

    KAUST Repository

    Cossu, Fabrizio

    2014-07-28

    By first-principles calculations we investigate the structural, electronic, and magnetic properties of the (LaMnO3)2/(SrTiO3)2 superlattice. We find that a monoclinic C2h symmetry is energetically favorable and that the spins order ferromagnetically. Under both compressive and tensile uniaxial strain the electronic structure of the superlattice shows a half-metallic character. In particular, a fully spin-polarized two-dimensional electron gas, which traces back to the Ti 3dxy orbitals, is achieved under compressive uniaxial strain. The (LaMnO3)2/(SrTiO3)2 superlattice is analysed with respect to its structure, magnetism, and electronic properties. Our results demonstrate that uniaxial strain in an experimentally accessible range, both tensile and compressive, can be used to induce half-metallicity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Signatures of field induced spin polarization of neutron star matter in seismic vibrations of paramagnetic neutron star

    International Nuclear Information System (INIS)

    Bastrukov, S I; Yang, J; Podgainy, D V; Weber, F

    2003-01-01

    A macroscopic model of the dissipative magneto-elastic dynamics of viscous spin polarized nuclear matter is discussed in the context of seismic activity of a paramagnetic neutron star. The source of the magnetic field of such a star is attributed to Pauli paramagnetism of baryon matter promoted by a seed magnetic field frozen into the star in the process of gravitational collapse of a massive progenitor. Particular attention is given to the effect of shear viscosity of incompressible stellar material on the timing of non-radial torsional magneto-elastic pulsations of the star triggered by starquakes. By accentuating the fact that this kind of vibration is unique to the seismology of a paramagnetic neutron star we show that the high-frequency modes decay faster than the low-frequency modes. The obtained analytic expressions for the period and relaxation time of this mode, in which the magnetic susceptibility and viscosity enter as input parameters, are then quantified by numerical estimates for these parameters taken from early and current works on transport coefficients of dense matter. It is found that the effect of viscosity is crucial for the lifetime of magneto-torsion vibrations but it does not appreciably affect the periods of this seismic mode which fall in the realm of periods of pulsed emission of soft gamma-ray repeaters and anomalous x-ray pulsars - young super-magnetized neutron stars, radiating, according to the magnetar model, at the expense of the magnetic energy release. Finally, we present arguments that the long periodic pulsed emission of these stars in a quiescent regime of radiation can be interpreted as a manifestation of weakly damped seismic magneto-torsion vibrations exhibiting the field induced spin polarization of baryon matter

  7. Theory for Spin Selective Andreev Re ection in Vortex Core of Topological Superconductor: Majorana Zero Modes on Spherical Surface and Application to Spin Polarized Scanning Tunneling Microscope Probe

    Science.gov (United States)

    Zhang, Fu-Chun; Hu, Lun-Hui; Li, Chuang; Xu, Dong-Hui; Zhou, Yi

    Majorana zero modes (MZMs) have been predicted to exist in the topological insulator (TI)/superconductor (SC) heterostructure. Recent spin polarized scanning tunneling microscope(STM) experiment has observed spin-polarization dependence of the zero bias differential tunneling conductance at the center of vortex core. Here we consider a helical electron system described by a Rashba spin orbit coupling Hamiltonian on a spherical surface with a s-wave superconducting pairing due to proximity effect. We examine in-gap excitations of a pair of vortices with one at the north pole and the other at the south pole. While the MZM is not a spin eigenstate, the spin wavefunction of the MZM at the center of the vortex core, r = 0, is parallel to the magnetic field, and the local Andreev reflection of the MZM is spin selective, namely occurs only when the STM tip has the spin polarization parallel to the magnetic field, similar to the case in 1-dimensional nanowire. The total local differential tunneling conductance consists of the normal term proportional to the local density of states and an additional term arising from the Andreev reflection. We apply our theory to examine the recently reported spin-polarized STM experiments and show good agreement with the experiments

  8. Accurate first principles calculation of many-body interactions

    International Nuclear Information System (INIS)

    Tawa, G.J.; Moskowitz, J.W.; Schmidt, K.E.

    1991-01-01

    This paper reports on the electronic structure Schrodinger equation that is solved for the van der Waals complexes spin-polarized H 2 and H 3 , and the closed-shell systems He 2 and He 3 by Monte Carlo methods. Two types of calculations are performed, variational Monte Carlo, which gives an upper bound to the eigenvalue of the Schrodinger equation, and Green's function Monte Carlo, which can solve the Schrodinger equation exactly within statistical sampling errors. The simulations are carried out on an ETA-10 supercomputer, and already existing computer codes were extensively modified to ensure highly efficient coding. A major component of the computations was the development of highly optimized many-electron wave functions. The results from the variational Monte Carlo simulations are reported for both the two- and three-body interaction energies

  9. Giving presentations

    CERN Document Server

    Ellis, Mark

    1997-01-01

    This is part of a series of books, which gives training in key business communication skills. Emphasis is placed on building awareness of language appropriateness and fluency in typical business interactions. This new edition is in full colour.

  10. Regular and irregular dynamics of spin-polarized wavepackets in a mesoscopic quantum dot at the edge of topological insulator

    Energy Technology Data Exchange (ETDEWEB)

    Khomitsky, D. V., E-mail: khomitsky@phys.unn.ru; Chubanov, A. A.; Konakov, A. A. [Lobachevsky National Research State University of Nizhny Novgorod, Department of Physics (Russian Federation)

    2016-12-15

    The dynamics of Dirac–Weyl spin-polarized wavepackets driven by a periodic electric field is considered for the electrons in a mesoscopic quantum dot formed at the edge of the two-dimensional HgTe/CdTe topological insulator with Dirac–Weyl massless energy spectra, where the motion of carriers is less sensitive to disorder and impurity potentials. It is observed that the interplay of strongly coupled spin and charge degrees of freedom creates the regimes of irregular dynamics in both coordinate and spin channels. The border between the regular and irregular regimes determined by the strength and frequency of the driving field is found analytically within the quasiclassical approach by means of the Ince–Strutt diagram for the Mathieu equation, and is supported by full quantum-mechanical simulations of the driven dynamics. The investigation of quasienergy spectrum by Floquet approach reveals the presence of non-Poissonian level statistics, which indicates the possibility of chaotic quantum dynamics and corresponds to the areas of parameters for irregular regimes within the quasiclassical approach. We find that the influence of weak disorder leads to partial suppression of the dynamical chaos. Our findings are of interest both for progress in the fundamental field of quantum chaotic dynamics and for further experimental and technological applications of spindependent phenomena in nanostructures based on topological insulators.

  11. Signatures of field induced spin polarization of neutron star matter in seismic vibrations of paramagnetic neutron star

    CERN Document Server

    Bastrukov, S I; Podgainy, D V; Weber, F

    2003-01-01

    A macroscopic model of the dissipative magneto-elastic dynamics of viscous spin polarized nuclear matter is discussed in the context of seismic activity of a paramagnetic neutron star. The source of the magnetic field of such a star is attributed to Pauli paramagnetism of baryon matter promoted by a seed magnetic field frozen into the star in the process of gravitational collapse of a massive progenitor. Particular attention is given to the effect of shear viscosity of incompressible stellar material on the timing of non-radial torsional magneto-elastic pulsations of the star triggered by starquakes. By accentuating the fact that this kind of vibration is unique to the seismology of a paramagnetic neutron star we show that the high-frequency modes decay faster than the low-frequency modes. The obtained analytic expressions for the period and relaxation time of this mode, in which the magnetic susceptibility and viscosity enter as input parameters, are then quantified by numerical estimates for these parameter...

  12. Design and optimization of a modular setup for measurements of three-dimensional spin polarization with ultrafast pulsed sources

    Energy Technology Data Exchange (ETDEWEB)

    Pincelli, T., E-mail: pincelli@iom.cnr.it; Rossi, G. [Dipartimento di Fisica, Università degli studi di Milano, Via Celoria 16, 20133 Milano (Italy); Laboratorio TASC, IOM-CNR, S.S. 14 km 163.5, Basovizza, 34149 Trieste (Italy); Petrov, V. N. [Saint Petersburg State Polytechnical University, Politechnicheskaya Street 29, 195251 Saint Petersburg (Russian Federation); Brajnik, G.; Carrato, S. [Università degli Studi di Trieste, Piazzale Europa 1, 34127 Trieste (Italy); Ciprian, R.; Torelli, P.; Krizmancic, D.; Salvador, F.; De Luisa, A.; Panaccione, G. [Laboratorio TASC, IOM-CNR, S.S. 14 km 163.5, Basovizza, 34149 Trieste (Italy); Lollobrigida, V. [Dipartimento di Matematica e Fisica, Università Roma Tre, I-00146 Rome (Italy); Sergo, R.; Gubertini, A.; Cautero, G. [Sincrotrone Trieste S.C.p.A, Strada Statale 14-km 163.5 in AREA Science Park, Basovizza, 34149 Trieste (Italy)

    2016-03-15

    ULTRASPIN is an apparatus devoted to the measurement of the spin polarization (SP) of electrons ejected from solid surfaces in a UHV environment. It is designed to exploit ultrafast light sources (free electron laser or laser high harmonic generation) and to perform (photo)electron spin analysis by an arrangement of Mott scattering polarimeters that measure the full SP vector. The system consists of two interconnected UHV vessels: one for surface science sample cleaning treatments, e-beam deposition of ultrathin films, and low energy electron diffraction/AES characterization. The sample environment in the polarimeter allows for cryogenic cooling and in-operando application of electric and magnetic fields. The photoelectrons are collected by an electrostatic accelerator and transport lens that form a periaxial beam that is subsequently directed by a Y-shaped electrostatic deflector to either one of the two orthogonal Mott polarimeters. The apparatus has been designed to operate in the extreme conditions of ultraintense single-X-ray pulses as originated by free electron lasers (up to 1 kHz), but it allows also for the single electron counting mode suitable when using statistical sources such as synchrotron radiation, cw-laser, or e-gun beams (up to 150 kcps).

  13. Design and optimization of a modular setup for measurements of three-dimensional spin polarization with ultrafast pulsed sources

    Science.gov (United States)

    Pincelli, T.; Petrov, V. N.; Brajnik, G.; Ciprian, R.; Lollobrigida, V.; Torelli, P.; Krizmancic, D.; Salvador, F.; De Luisa, A.; Sergo, R.; Gubertini, A.; Cautero, G.; Carrato, S.; Rossi, G.; Panaccione, G.

    2016-03-01

    ULTRASPIN is an apparatus devoted to the measurement of the spin polarization (SP) of electrons ejected from solid surfaces in a UHV environment. It is designed to exploit ultrafast light sources (free electron laser or laser high harmonic generation) and to perform (photo)electron spin analysis by an arrangement of Mott scattering polarimeters that measure the full SP vector. The system consists of two interconnected UHV vessels: one for surface science sample cleaning treatments, e-beam deposition of ultrathin films, and low energy electron diffraction/AES characterization. The sample environment in the polarimeter allows for cryogenic cooling and in-operando application of electric and magnetic fields. The photoelectrons are collected by an electrostatic accelerator and transport lens that form a periaxial beam that is subsequently directed by a Y-shaped electrostatic deflector to either one of the two orthogonal Mott polarimeters. The apparatus has been designed to operate in the extreme conditions of ultraintense single-X-ray pulses as originated by free electron lasers (up to 1 kHz), but it allows also for the single electron counting mode suitable when using statistical sources such as synchrotron radiation, cw-laser, or e-gun beams (up to 150 kcps).

  14. Improved Electron Yield and Spin-Polarization from III-V Photocathodes Via Bias Enhanced Carrier Drift

    CERN Document Server

    Mulhollan, Gregory A; Brachmann, Axel; Clendenin, James E; Garwin, Edward; Kirby, Robert; Luh Dah An; Maruyama, Takashi; Prepost, Richard

    2005-01-01

    Spin-polarized electrons are commonly used in high energy physics. Future work will benefit from greater polarization. Polarizations approaching 90% have been achieved at the expense of yield. The primary paths to higher polarization are material design and electron transport. Our work addresses the latter. Photoexcited electrons may be preferentially emitted or suppressed by an electric field applied across the active region. We are tuning this forward bias for maximum polarization and yield, together with other parameters, e.g., doping profile Preliminary measurements have been carried out on bulk GaAs. As expected, the yield change far from the bandgap is quite large. The bias is applied to the bottom (non-activated) side of the cathode so that the accelerating potential as measured with respect to the ground potential chamber walls is unchanged for different front-to-back cathode bias values. For a bias which enhances emission, the yield nearly doubles. For a bias which diminishes emission, the yield is a...

  15. Magnetism in grain-boundary phase of a NdFeB sintered magnet studied by spin-polarized scanning electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kohashi, Teruo, E-mail: teruo.kohashi.fc@hitachi.com; Motai, Kumi [Central Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-0395 (Japan); Nishiuchi, Takeshi; Hirosawa, Satoshi [Magnetic Materials Research Laboratory, Hitachi Metals Ltd., Osaka 618-0013 (Japan)

    2014-06-09

    The magnetism in the grain-boundary phase of a NdFeB sintered magnet was measured by spin-polarized scanning electron microscopy (spin SEM). A sample magnet was fractured in the ultra-high-vacuum chamber to avoid oxidation, and its magnetizations in the exposed grain-boundary phase on the fracture surface were evaluated through the spin polarization of secondary electrons. Spin-SEM images were taken as the fracture surface was milled gradually by argon ions, and the magnetization in the grain-boundary phase was quantitatively obtained separately from that of the Nd{sub 2}Fe{sub 14}B phase. The obtained magnetization shows that the grain-boundary phase of this magnet has substantial magnetization, which was confirmed to be ferromagnetic.

  16. Spin-polarized electron gas in Co2MSi/SrTiO3(M= Ti, V, Cr, Mn, and Fe) heterostructures

    KAUST Repository

    Nazir, S.

    2016-06-08

    Spin-polarized density functional theory is used to study the TiO2 terminated interfaces between the magnetic Heusler alloys Co2Si (M = Ti, V, Cr, Mn, and Fe) and the non-polar band insulator SrTiO3. The structural relaxation at the interface turns out to depend systematically on the lattice mis- match. Charge transfer from the Heusler alloys (mainly the M 3d orbitals) to the Ti dxy orbitals of the TiO2 interface layer is found to gradually grow from M = Ti to Fe, resulting in an electron gas with increasing density of spin-polarized charge carriers. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  17. Mechanism of ({sup 14}N, {sup 12}B) reactions at intermediate energy leading to large spin-polarization of {sup 12}B

    Energy Technology Data Exchange (ETDEWEB)

    Mitsuoka, Shin-ichi [Osaka Univ., Ibaraki (Japan). Research Center for Nuclear Physics; Shimoda, Tadashi; Miyatake, Hiroari [and others

    1996-05-01

    To study mechanisms of the ({sup 14}N, {sup 12}B) reactions at intermediate energies, double differential cross section and nuclear spin-polarization of the {sup 12}B projectile-like fragments have been measured as a function of longitudinal momentum in the angular range of 0deg - 9deg. Large spin-polarization of the reaction products {sup 12}B has been observed in the {sup 9}Be({sup 14}N, {sup 12}B) reaction at 39.3 MeV/u. The momentum distributions at forward angles exhibit characteristic features which can not be understood by the current projectile fragmentation picture. It is shown that by assuming the existence of direct two-proton transfer process in addition to the fragmentation process, both the cross section and polarization of {sup 12}B fragments are successfully explained. The target and incident energy dependence of the momentum distribution are also explained reasonably. (author)

  18. Spin-dependent scattering and the spin polarization of a diffusive current in partly disordered L10 epitaxial FePd

    International Nuclear Information System (INIS)

    Seemann, K M; Hickey, M C; Baltz, V; Hickey, B J; Marrows, C H

    2010-01-01

    We report magnetic domain wall (DW) resistance in epitaxial films of FePd. When equal numbers of Fe and Pd atoms are present, this material forms an ordered structure with alternating crystal planes of Fe and Pd. We prepared films enriched with Pd to varying degrees, gradually degrading this structure. As might be expected, this increased the electrical resistivity of the films by introducing extra defects that can scatter electrons. However, unexpectedly, the additional resistance arising from the ∼10 nm thick DWs rose as a proportion of the overall resistivity, roughly doubling when halving the degree of chemical ordering-as determined from x-ray diffraction measurements-within the films. These data can be used to infer a rise in the spin polarization of the current flowing in the layers when extra Pd atoms are introduced. On the other hand, a separate measurement of spin polarization using a superconducting point contact technique that is insensitive to electron scattering revealed no changes as extra Pd was introduced. We conclude that Pd atoms scatter electrons of one spin far more strongly than the other, suggesting a possible means of producing highly spin-polarized currents for use in spintronic devices.

  19. Spin-polarized high-energy scattering of charged leptons on nucleons

    Energy Technology Data Exchange (ETDEWEB)

    Burkardt, Matthias; Nowak, Wolf-Dieter; MILLER, A.

    2009-01-01

    The proton is a composite object with spin one-half, understood to contain highly relativistic spin one-half quarks exchanging spin-one gluons, each possibly with significant orbital angular momenta. While their fundamental interactions are well described by Quantum ChromoDynamics (QCD), our standard theory of the strong interaction, nonperturbative calculations of the internal structure of the proton based directly on QCD are beginning to provide reliable results. Most of our present knowledge of the structure of the proton is based on experimental measurements interpreted within the rich framework of QCD. An area presently attracting intense interest, both experimental and theoretical, is the relationship between the spin of the proton and the spins and orbital angular momenta of its constituents. While remarkable progress has been made, especially in the last decade, the discovery and investigation of new concepts have revealed that much more remains to be learned. This progress i

  20. Spin-polarized high-energy scattering of charged leptons on nucleons

    Energy Technology Data Exchange (ETDEWEB)

    Burkardt, M. [New Mexico State Univ., Las Cruces, NM (United States). Dept. of Physics; Miller, C.A. [TRIUMF, Vancouver, BC (Canada); Nowak, W.D. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany)

    2009-08-15

    The proton is a composite object with spin one-half, understood to contain highly relativistic spin one-half quarks exchanging spin-one gluons, each possibly with significant orbital angular momenta. While their fundamental interactions are well described by Quantum ChromoDynamics (QCD), our standard theory of the strong interaction, nonperturbative calculations of the internal structure of the proton based directly on QCD are beginning to provide reliable results. Most of our present knowledge of the structure of the proton is based on experimental measurements interpreted within the rich framework of QCD. An area presently attracting intense interest, both experimental and theoretical, is the relationship between the spin of the proton and the spins and orbital angular momenta of its constituents. While remarkable progress has been made, especially in the last decade, the discovery and investigation of new concepts have revealed that much more remains to be learned. This progress is reviewed and an outlook for the future is offered. (orig.)

  1. Influence of doping admixture and anisotropic tension on behaviour of muon spin polarization in insulators

    International Nuclear Information System (INIS)

    Gorelkin, V.N.; Rubtsov, D.V.

    1997-01-01

    We investigate the model describing a muon tunneling between two equivalent positions in (magnetic) insulators. Crystals are assumed to have concentrations such that the muon tunneling states in a double well potential can be considered as real during the muon lifetime τ μ . In the simplest model there are only two such states: the ground state and the first excited state. Our aim is to calculate lifetimes τ 1 (T) and τ 0 (T) of these muon tunneling states resulting from interaction between the muon and phonons of the sample. In the case of a distorted double well potential, all matrix elements of H-circumflex (ph) int are finite. This leads to rescaling of the first and second orders of the perturbation theory compared with the results for the muon in 'pure' samples. We explain the vanishing of some part of the oscillation frequencies of the muon polarization vector in the framework of a muon-phonon interaction model: for example, it is necessary to take into account that τ 1 (T) decreases more rapidly than τ 0 (T) when the temperature increases. If the muon tunnels through a set of equivalent interstitial positions in a unit cell, the experimental picture of the polarization vector behaviour can change drastically under the action of various strain fields

  2. Co on Pt(111) studied by spin-polarized scanning tunneling microscopy and spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Meier, F.K.

    2006-07-01

    In this thesis the electronic properties of the bare Pt(111) surface, the structural, electronic, and magnetic properties of monolayer and double-layer high Co nanostructures as well as the spin-averaged electronic structure of single Co atoms on Pt(111) were studied by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The experiments on the bare Pt(111) surface and on single Co atoms have been performed in an STM facility operating at temperatures of down to 0.3 K and at magnetic fields of up to 14 T under ultra-high vacuum conditions. The facility has been taken into operation within the time period of this thesis and its specifications were tested by STS measurements. These characterization measurements show a very high stability of the tunneling junction and an energy resolution of about 100 {mu}eV, which is close to the thermal limit. The investigation of the electronic structure of the bare Pt(111) surface reveals the existence of an unoccupied surface state. By a comparison of the measured dispersion to first-principles electronic structure calculations the state is assigned to an sp-derived surface band at the lower boundary of the projected bulk band gap. The surface state exhibits a strong spin-orbit coupling induced spin splitting. The close vicinity to the bulk bands leads to a strong linear contribution to the dispersion and thus to a deviant appearance in the density of states in comparison to the surface states of the (111) surfaces of noble metals. A detailed study of Co monolayer and double-layer nanostructures on the Pt(111) surface shows that both kinds of nanostructures exhibit a highly inhomogeneous electronic structure which changes at the scale of only a few Aa due to a strong stacking dependence with respect to the Pt(111) substrate. With the help of first principles calculations the different spectroscopic appearance for Co atoms within the Co monolayer is assigned to a stacking dependent hybridization of Co states

  3. Tuning Fermi level of Cr{sub 2}CoZ (Z=Al and Si) inverse Heusler alloys via Fe-doping for maximum spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India); Saini, Hardev S. [Department of Physics, Panjab University, Chandigarh-160014 (India); Thakur, Jyoti [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India); Reshak, Ali H. [New Technologies—Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India)

    2014-12-15

    We report full potential treatment of electronic and magnetic properties of Cr{sub 2−x}Fe{sub x}CoZ (Z=Al, Si) Heusler alloys where x=0.0, 0.25, 0.5, 0.75 and 1.0, based on density functional theory (DFT). Both parent alloys (Cr{sub 2}CoAl and Cr{sub 2}CoSi) are not half-metallic frromagnets. The gradual replacement of one Cr sublattice with Fe induces the half-metallicity in these systems, resulting maximum spin polarization. The half-metallicity starts to appear in Cr{sub 2−x}Fe{sub x}CoAl and Cr{sub 2−x}Fe{sub x}CoSi with x=0.50 and x=0.25, respectively, and the values of minority-spin gap and half-metallic gap or spin-flip gap increase with further increase of x. These gaps are found to be maximum for x=1.0 for both cases. An excellent agreement between the structural properties of CoFeCrAl with available experimental study is obtained. The Fermi level tuning by Fe-doping makes these alloys highly spin polarized and thus these can be used as promising candidates for spin valves and magnetic tunnelling junction applications. - Highlights: • Tuning of E{sub F} in Cr{sub 2}CoZ (Z=Al, Si) has been demonstrated via Fe doping. • Effect of Fe doping on half-metallicity and magnetism have been discussed. • The new alloys have a potential of being used as spin polarized electrodes.

  4. Excitation of Self-Localized Spin-Wave Bullets by Spin-Polarized Current in In-Plane Magnetized Magnetic Nano-Contacts: A Micromagnetic Study

    Science.gov (United States)

    2007-10-08

    excitation of microwave spin waves.3,10,11 The analytical theory of spin-wave excitation in magnetic nanocontacts by spin-polarized current performed...linear theory ,3 the propagating spin- wave mode excited at the threshold is a cylindrical spin- wave with the wave vector kL=1.2/Rc and frequency L... Oersted magnetic field, and/or by any other small interaction, neglected in the micromagnetic model. To make the excitation of subcritical modes12,15

  5. Calculated Specific Volumes and Magnetic Moments of the 3d Transition Metal Monoxides

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt; Andersen, O. K.; Johansson, B.

    1980-01-01

    We have performed self-consistent, spin-polarized band structure calculations as a function of the lattice spacing for the 3d metal monoxides in order to obtain the equilibrium lattice constants. The calculated binding from the 3d electrons and the occurrence of antiferromagnetism account...

  6. Direct evidence of hidden local spin polarization in a centrosymmetric superconductor LaO0.55F0.45BiS2.

    Science.gov (United States)

    Wu, Shi-Long; Sumida, Kazuki; Miyamoto, Koji; Taguchi, Kazuaki; Yoshikawa, Tomoki; Kimura, Akio; Ueda, Yoshifumi; Arita, Masashi; Nagao, Masanori; Watauchi, Satoshi; Tanaka, Isao; Okuda, Taichi

    2017-12-04

    Conventional Rashba spin polarization is caused by the combination of strong spin-orbit interaction and spatial inversion asymmetry. However, Rashba-Dresselhaus-type spin-split states are predicted in the centrosymmetric LaOBiS 2 system by recent theory, which stem from the local inversion asymmetry of active BiS 2 layer. By performing high-resolution spin- and angle-resolved photoemission spectroscopy, we have investigated the electronic band structure and spin texture of superconductor LaO 0.55 F 0.45 BiS 2 . Here we present direct spectroscopic evidence for the local spin polarization of both the valence band and the conduction band. In particular, the coexistence of Rashba-like and Dresselhaus-like spin textures has been observed in the conduction band. The finding is of key importance for fabrication of proposed dual-gated spin-field effect transistor. Moreover, the spin-split band leads to a spin-momentum locking Fermi surface from which superconductivity emerges. Our demonstration not only expands the scope of spintronic materials but also enhances the understanding of spin-orbit interaction-related superconductivity.

  7. Energy spectrum, the spin polarization, and the optical selection rules of the Kronig-Penney superlattice model with spin-orbit coupling

    Science.gov (United States)

    Li, Rui

    2018-02-01

    The Kronig-Penney model, an exactly solvable one-dimensional model of crystal in solid physics, shows how the allowed and forbidden bands are formed in solids. In this paper, we study this model in the presence of both strong spin-orbit coupling and the Zeeman field. We analytically obtain four transcendental equations that represent an implicit relation between the energy and the Bloch wave vector. Solving these four transcendental equations, we obtain the spin-orbital bands exactly. In addition to the usual band gap opened at the boundary of the Brillouin zone, a much larger spin-orbital band gap is also opened at some special sites inside the Brillouin zone. The x component of the spin-polarization vector is an even function of the Bloch wave vector, while the z component of the spin-polarization vector is an odd function of the Bloch wave vector. At the band edges, the optical transition rates between adjacent bands are nonzero.

  8. Very efficient spin polarization analysis (VESPA): new exchange scattering-based setup for spin-resolved ARPES at APE-NFFA beamline at Elettra.

    Science.gov (United States)

    Bigi, Chiara; Das, Pranab K; Benedetti, Davide; Salvador, Federico; Krizmancic, Damjan; Sergo, Rudi; Martin, Andrea; Panaccione, Giancarlo; Rossi, Giorgio; Fujii, Jun; Vobornik, Ivana

    2017-07-01

    Complete photoemission experiments, enabling measurement of the full quantum set of the photoelectron final state, are in high demand for studying materials and nanostructures whose properties are determined by strong electron and spin correlations. Here the implementation of the new spin polarimeter VESPA (Very Efficient Spin Polarization Analysis) at the APE-NFFA beamline at Elettra is reported, which is based on the exchange coupling between the photoelectron spin and a ferromagnetic surface in a reflectometry setup. The system was designed to be integrated with a dedicated Scienta-Omicron DA30 electron energy analyzer allowing for two simultaneous reflectometry measurements, along perpendicular axes, that, after magnetization switching of the two targets, allow the three-dimensional vectorial reconstruction of the spin polarization to be performed while operating the DA30 in high-resolution mode. VESPA represents the very first installation for spin-resolved ARPES (SPARPES) at the Elettra synchrotron in Trieste, and is being heavily exploited by SPARPES users since autumn 2015.

  9. Spin-polarized 3He nuclear targets and metastable 4He atoms by optical pumping with a tunable, Nd:YAP laser

    International Nuclear Information System (INIS)

    Bohler, C.L.; Schearer, L.D.; Leduc, M.; Nacher, P.J.; Zachorowski, L.; Milner, R.G.; McKeown, R.D.; Woodward, C.E.

    1988-01-01

    Several Nd:YAP lasers were constructed which could be broadly tuned in the 1083-nm region which includes the helium 2 3 S-2 3 P transition, using a Lyot filter and thin, uncoated etalons within the laser cavity. 1 W of power could be extracted at 1083 nm through a 1% transmitting output coupler. This laser beam was used to optically pump metastable 4 He and 3 He 2 3 S helium atoms in a weak discharge cell, spin polarizing the metastable ensemble. In a 3 He cell the polarization is transferred to the nuclear spin system. A 3 He target cell at 0.3 Torr was polarized to 52% in a few minutes. We describe the application of this system to the design of polarized targets for experiments in nuclear physics

  10. Thomas-Fermi-von Weizsäcker theory for a harmonically trapped, two-dimensional, spin-polarized dipolar Fermi gas

    Science.gov (United States)

    van Zyl, B. P.; Zaremba, E.; Pisarski, P.

    2013-04-01

    We systematically develop a density functional description for the equilibrium properties of a two-dimensional, harmonically trapped, spin-polarized dipolar Fermi gas based on the Thomas-Fermi-von Weizsäcker approximation. We pay particular attention to the construction of the two-dimensional kinetic energy functional, where corrections beyond the local density approximation must be motivated with care. We also present an intuitive derivation of the interaction energy functional associated with the dipolar interactions and provide physical insight into why it can be represented as a local functional. Finally, a simple and highly efficient self-consistent numerical procedure is developed to determine the equilibrium density of the system for a range of dipole interaction strengths.

  11. Spin-polarization dependent carrier recombination dynamics and spin relaxation mechanism in asymmetrically doped (110) n-GaAs quantum wells

    Science.gov (United States)

    Teng, Lihua; Jiang, Tianran; Wang, Xia; Lai, Tianshu

    2018-05-01

    Carrier recombination and electron spin relaxation dynamics in asymmetric n-doped (110) GaAs/AlGaAs quantum wells are investigated with time-resolved pump-probe spectroscopy. The experiment results reveal that the measured carrier recombination time depends strongly on the polarization of pump pulse. With the same pump photon flux densities, the recombination time of spin-polarized carriers is always longer than that of the spin-balanced carriers except at low pump photon flux densities, this anomaly originates from the polarization-sensitive nonlinear absorption effect. Differing from the traditional views, in the low carrier density regime, the D'yakonov-Perel' (DP) mechanism can be more important than the Bir-Aronov-Pikus (BAP) mechanism, since the DP mechanism takes effect, the spin relaxation time in (110) GaAs QWs is shortened obviously via asymmetric doping.

  12. K-edge x-ray dichroism investigation of Fe1-xCoxSi: Experimental evidence for spin polarization crossover

    Science.gov (United States)

    Hearne, G. R.; Diguet, G.; Baudelet, F.; Itié, J.-P.; Manyala, N.

    2015-04-01

    Both Fe and Co K-edge x-ray magnetic circular dichroism (XMCD) have been employed as element-specific probes of the magnetic moments in the composition series of the disordered ferromagnet Fe1-xCoxSi (for x=0.2, 0.3, 0.4, 0.5). A definitive single peaked XMCD profile occurs for all compositions at both Fe and Co K-edges. The Fe 4p orbital moment, deduced from the integral of the XMCD signal, has a steep dependence on x at low doping levels and evolves to a different (weaker) dependence at x≥0.3, similar to the behavior of the magnetization in the Co composition range studied here. It is systematically higher, by at least a factor of two, than the corresponding Co orbital moment for most of the composition series. Fine structure beyond the K-edge absorption (limited range EXAFS) suggests that the local order (atomic environment) is very similar across the series, from the perspective of both the Fe and Co absorbing atom. The variation in the XMCD integral across the Co composition range has two regimes, that which occurs below x=0.3 and then evolves to different behavior at higher doping levels. This is more conspicuously present in the Fe contribution. This is rationalized as the evolution from a half-metallic ferromagnet at low Co doping to that of a strong ferromagnet at x>0.3 and as such, spin polarization crossover occurs. The Fermi level is tuned from the majority spin band for x<0.3 where a strongly polarized majority spin electron gas prevails, to a regime where minority spin carriers dominate at higher doping. The evolution of the Fe-derived spin polarized (3d) bands, indirectly probed here via the 4p states, is the primary determinant of the doping dependence of the magnetism in this alloy series.

  13. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    Science.gov (United States)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  14. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    International Nuclear Information System (INIS)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R.

    2014-01-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  15. Magnetic and electronic properties of strontium hexaferrite SrFe12O19 from first-principles calculations

    NARCIS (Netherlands)

    Fang, C.M.; Kools, F.; Metselaar, R.; With, G. de; Groot, R.A. de

    2003-01-01

    The magnetic and electronic structure of strontium hexaferrite SrFe12O19 has been investigated using density functional theory within the local spin density approximation. The calculations show that in this ferrite all the Fe3+ ions are fully spin polarized with S = 5/2. The electronic structure of

  16. Calculated surface-energy anomaly in the 3d metals

    DEFF Research Database (Denmark)

    Aldén, M.; Skriver, Hans Lomholt; Mirbt, S.

    1992-01-01

    Local-spin-density theory and a Green’s-function technique based on the linear muffin-tin orbitals method have been used to calculate the surface energy of the 3d metals. The theory explains the variation of the values derived from measurements of the surface tension of liquid metals including...... the pronounced anomaly occurring between vanadium and nickel in terms of a decrease in the d contribution caused by spin polarization....

  17. Observation of layered antiferromagnetism in self-assembled parallel NiSi nanowire arrays on Si(110) by spin-polarized scanning tunneling spectromicroscopy

    Science.gov (United States)

    Hong, Ie-Hong; Hsu, Hsin-Zan

    2018-03-01

    The layered antiferromagnetism of parallel nanowire (NW) arrays self-assembled on Si(110) have been observed at room temperature by direct imaging of both the topographies and magnetic domains using spin-polarized scanning tunneling microscopy/spectroscopy (SP-STM/STS). The topographic STM images reveal that the self-assembled unidirectional and parallel NiSi NWs grow into the Si(110) substrate along the [\\bar{1}10] direction (i.e. the endotaxial growth) and exhibit multiple-layer growth. The spatially-resolved SP-STS maps show that these parallel NiSi NWs of different heights produce two opposite magnetic domains, depending on the heights of either even or odd layers in the layer stack of the NiSi NWs. This layer-wise antiferromagnetic structure can be attributed to an antiferromagnetic interlayer exchange coupling between the adjacent layers in the multiple-layer NiSi NW with a B2 (CsCl-type) crystal structure. Such an endotaxial heterostructure of parallel magnetic NiSi NW arrays with a layered antiferromagnetic ordering in Si(110) provides a new and important perspective for the development of novel Si-based spintronic nanodevices.

  18. A modular designed ultra-high-vacuum spin-polarized scanning tunneling microscope with controllable magnetic fields for investigating epitaxial thin films.

    Science.gov (United States)

    Wang, Kangkang; Lin, Wenzhi; Chinchore, Abhijit V; Liu, Yinghao; Smith, Arthur R

    2011-05-01

    A room-temperature ultra-high-vacuum scanning tunneling microscope for in situ scanning freshly grown epitaxial films has been developed. The core unit of the microscope, which consists of critical components including scanner and approach motors, is modular designed. This enables easy adaptation of the same microscope units to new growth systems with different sample-transfer geometries. Furthermore the core unit is designed to be fully compatible with cryogenic temperatures and high magnetic field operations. A double-stage spring suspension system with eddy current damping has been implemented to achieve ≤5 pm z stability in a noisy environment and in the presence of an interconnected growth chamber. Both tips and samples can be quickly exchanged in situ; also a tunable external magnetic field can be introduced using a transferable permanent magnet shuttle. This allows spin-polarized tunneling with magnetically coated tips. The performance of this microscope is demonstrated by atomic-resolution imaging of surface reconstructions on wide band-gap GaN surfaces and spin-resolved experiments on antiferromagnetic Mn(3)N(2)(010) surfaces.

  19. Calculated magnetization of iron-cobalt disordered alloys

    International Nuclear Information System (INIS)

    Victora, R.H.; Falicov, L.M.

    1984-01-01

    The spin polarization of the disordered Fe-Co alloy was calculated using a tight-binding scheme, with single-site, full-orbital interactions treated self-consistently. Disorder is introduced by the use of the virtual-crystal approximation. Excellent agreement with the experimental spin polarization is obtained and the unusual shape of the Fe-Co curve on the Slater-Pauling plot is explained. The magnetization of the Co-rich alloys essentially depends on the number of available d holes, while the magnetization of the Fe-rich alloys is influenced by a relatively weak electron-electron interaction. The intersection of the two effects occurs at approximately 30 at. % Co and produces a maximum

  20. Spin-polarized electron tunneling in bcc FeCo/MgO/FeCo(001) magnetic tunnel junctions.

    Science.gov (United States)

    Bonell, F; Hauet, T; Andrieu, S; Bertran, F; Le Fèvre, P; Calmels, L; Tejeda, A; Montaigne, F; Warot-Fonrose, B; Belhadji, B; Nicolaou, A; Taleb-Ibrahimi, A

    2012-04-27

    In combining spin- and symmetry-resolved photoemission, magnetotransport measurements and ab initio calculations we detangled the electronic states involved in the electronic transport in Fe(1-x)Co(x)(001)/MgO/Fe(1-x)Co(x)(001) magnetic tunnel junctions. Contrary to previous theoretical predictions, we observe a large reduction in TMR (from 530 to 200% at 20 K) for Co content above 25 atomic% as well as anomalies in the conductance curves. We demonstrate that these unexpected behaviors originate from a minority spin state with Δ(1) symmetry that exists below the Fermi level for high Co concentration. Using angle-resolved photoemission, this state is shown to be a two-dimensional state that occurs at both Fe(1-x)Co(x)(001) free surface, and more importantly at the interface with MgO. The combination of this interface state with the peculiar density of empty states due to chemical disorder allows us to describe in details the complex conduction behavior in this system.

  1. Unravelling the magnetism, high spin polarization and thermoelectric efficiency of ZrFeSi half-Heusler

    Science.gov (United States)

    Yousuf, Saleem; Gupta, D. C.

    2018-04-01

    We report the systematic investigation of structural properties, occupancy of density of states, nature of bonding and thermoelectric efficiency of half-Heusler ZrFeSi. The band structure analysis predicts the hybridization of Zr-d and Fe-d metal atoms resulting in occupation of density of states above the Fermi level (EF) while Fe-p and Si-p occupy the lower energy states below the EF. Thermoelectric transport coefficients are predicted using the Boltzmann transport theory under constant relaxation approximation, where Seebeck coefficient (S), total thermal conductivity and figure of merit are calculated. The negative value of total S as -14.02 μV/K predicts the material as n-type with thermoelectric figure of merit (zT) of 0.5 at 800 K. The lattice thermal conductivity decreases with increasing temperature with room temperature value of 4.18 W/mK and shows a significant reduction towards higher temperatures. In view of above elements, structural stability, high zT, ZrFeSi alloy have the capabilities to stimulate experimental verification as a promising materials for high temperature power generation and spintronic device fabrications.

  2. Cu–Ni core–shell nanoparticles: structure, stability, electronic, and magnetic properties: a spin-polarized density functional study

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Qiang, E-mail: wangqiang@njtech.edu.cn; Wang, Xinyan; Liu, Jianlan; Yang, Yanhui [Nanjing Tech University, School of Chemistry and Molecular Engineering, Institute of Advanced Synthesis (IAS) (China)

    2017-02-15

    Bimetallic core–shell nanoparticles (CSNPs) have attracted great interest not only because of their superior stability, selectivity, and catalytic activity but also due to their tunable properties achieved by changing the morphology, sequence, and sizes of both core and shell. In this study, the structure, stability, charge transfer, electronic, and magnetic properties of 13-atom and 55-atom Cu and Cu–Ni CSNPs were investigated using the density functional theory (DFT) calculations. The results show that Ni@Cu CSNPs with a Cu surface shell are more energetically favorable than Cu@Ni CSNPs with a Ni surface shell. Interestingly, three-shell Ni@Cu{sub 12}@Ni{sub 42} is more stable than two-shell Cu{sub 13}@Ni{sub 42}, while two-shell Ni{sub 13}@Cu{sub 42} is more stable than three-shell Cu@Ni{sub 12}@Cu{sub 42}. Analysis of Bader charge illustrates that the charge transfer increases from Cu core to Ni shell in Cu@Ni NPs, while it decreases from Ni core to Cu shell in Ni@Cu NPs. Furthermore, the charge transfer results that d-band states have larger shift toward the Fermi level for the Ni@Cu CSNPs with Cu surface shell, while the Cu@Ni CSNPs with Ni surface shell have similar d-band state curves and d-band centers with the monometallic Ni NPs. In addition, the Cu–Ni CSNPs possess higher magnetic moment when the Ni atoms aggregated at core region of CSNPs, while having lower magnetic moment when the Ni atoms segregate on surface region. The change of the Cu atom location in CSNPs has a weak effect on the total magnetic moment. Our findings provide useful insights for the design of bimetallic core–shell catalysts.

  3. Development, construction and characterization of a variable repetitive spin-polarized electron gun with an inverted-geometry insulator; Entwicklung, Aufbau und Charakterisierung einer variabel repetierenden, spinpolarisierten Elektronenkanone mit invertierter Isolatorgeometrie

    Energy Technology Data Exchange (ETDEWEB)

    Espig, Martin

    2016-02-15

    Within the scope of this thesis a pulsed source of spin polarized electrons Photo-CATCH was designed, constructed, characterized and has been put into operation. This source is based on the photoemission of spin-polarized electrons from GaAs-photocathodes. Both the design of the electron gun, consisting of an ultra-high vacuum chamber and an electrode with Pierce geometry, as well as the properties of the electron beam have been simulated with CST Studio. Results were a maximum electric field of (0.064±0.001) MV/m/kV on the electrode surface and a beam emittance as a function of the radius of the laser spot on the photocathode of element of {sub n,x}=(1.7478(4).10{sup -4}.(r)/(μm)+2.8(18).10{sup -5}) mm mrad at a beam current of 100 μA. Currently Photo-CATCH provides electron beams with an energy of 60 keV, which can be expanded up to 100 keV by upgrading the high-voltage power supply. The electron gun has an inverted-geometry insulator to ensure a compact design of the ultra-high vacuum chamber and a maximum person- and machine-safety from sparkovers. Since the properties of the laser light directly affect the properties of the generated electron beam a pulsed semiconductor laser system has been specially developed and built for Photo-CATCH. This is characterized by a high variability of its operating parameters, in particular its wavelength and repetition rate, in order to fulfill the broad variety of requirements of various nuclear physics experiments. By selecting the wavelength of the used laser diode highly polarized or high-current electron beams can be generated from GaAs-photocathodes. The time profile of the laser has direct influence to the longitudinal profile of the electron bunch. Through the radiofrequency modulation of the pumping current of the impedance-matched semiconductor laser system, consisting of a DC power source and an electrical pulse generator with 881 ps broad pump pulses, Lorentz shaped laser pulses with a minimum FWHM of (43.8±1

  4. Spin-polarized scanning tunneling microscopy of magnetic nanostructures at the example of bcc-Co/Fe(110), Fe/Mo(110), and copper phthalocyanine/Fe(1110); Spinpolarisierte Rastertunnelmikroskopie magnetischer Nanostrukturen am Beispiel von bcc-Co/Fe(110), Fe/Mo(110) und Kupfer-Phthalocyanin/Fe(110)

    Energy Technology Data Exchange (ETDEWEB)

    Methfessel, Torsten

    2010-12-09

    This thesis provides an introduction into the technique of spin-polarized scanning tunnelling microscopy and spectroscopy as an experimental method for the investigation of magnetic nanostructures. Experimental results for the spin polarized electronic structure depending on the crystal structure of ultrathin Co layers, and depending on the direction of the magnetization for ultrathin Fe layers are presented. High-resolution measurements show the position-dependent spin polarization on a single copper-phthalocyanine molecule deposited on a ferromagnetic surface. Co was deposited by molecular beam epitaxy on the (110) surface of the bodycentered cubic metals Cr and Fe. In contrast to previous reports in the literature only two layers of Co can be stabilized in the body-centered cubic (bcc) structure. The bcc-Co films on the Fe(110) surface show no signs of epitaxial distortions. Thicker layers reconstruct into a closed-packed structure (hcp / fcc). The bcc structure increases the spin-polarization of Co to P=62 % in comparison to hcp-Co (P=45 %). The temperature-dependent spin-reorientation of ultrathin Fe/Mo(110) films was investigated by spin-polarized spectroscopy. A reorientation of the magnetic easy axis from the [110] direction along the surface normal to the in-plane [001] axis is observed at T (13.2{+-}0.5) K. This process can be identified as a discontinuous reorientation transition, revealing two simultaneous minima of the free energy in a certain temperature range. The electronic structure of mono- and double-layer Fe/Mo(110) shows a variation with the reorientation of the magnetic easy axis and with the direction of the magnetization. The investigation of the spin-polarized charge transport through a copper-phthalocyanine molecule on the Fe/Mo(110) surface provides an essential contribution to the understanding of spin-transport at the interface between metal and organic molecule. Due to the interaction with the surface of the metal the HOMO-LUMO energy

  5. Giving Medicine to Children

    Science.gov (United States)

    ... Products For Consumers Home For Consumers Consumer Updates Articulos en Espanol Giving Medicine to Children Share Tweet ... right medicine and the right amount More in Articulos en Espanol Alimentos y Bebidas Cosméticos Dispositivos ...

  6. Ab-initio calculations of Co-based diluted magnetic semiconductors Cd 1-xCoxX (X=S, Se, Te)

    KAUST Repository

    Saeed, Yasir

    2010-10-01

    Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic semiconductors composed of IIVI compounds Cd1-xCoxX (X=S, Se, Te) at x=0.25. From the calculated results of band structure and density of states, the half-metallic character and stability of ferromagnetic state for Cd1-xCoxS, Cd1-xCoxSe and Cd 1-xCoxTe alloys are determined. It is found that the tetrahedral crystal field gives rise to triple degeneracy t2g and double degeneracy eg. Furthermore, we predict the values of spin-exchange splitting energies Δx(d) and Δ x(p-d) and exchange constants N0α and N 0β produced by the Co 3d states. Calculated total magnetic moments and the robustness of half-metallicity of Cd1-xCo xX (X=S, Se, Te) with respect to the variation in lattice parameters are also discussed. We also extend our calculations to x=0.50, 0.75 for S compounds in order to observe the change due to increase in Co. © 2010 Elsevier B.V.

  7. Give blood at CERN

    CERN Multimedia

    SC Unit

    2008-01-01

    ACCIDENTS and ILLNESSES don’t take a break! DO SOMETHING AMAZING - GIVE BLOOD! IT’S IN ALL OUR INTERESTS. 30 July 2008 from 9.30 a.m. to 4 p.m. CERN RESTAURANT NOVAE First floor - Salle des Pas Perdus After you have given blood, you are invited to partake of refreshments kindly offered by NOVAE.

  8. Spin-polarized scanning tunneling microscopy experiments on the rough surface of a polycrystalline NiFe film with a fine magnetic tip sensitive to a well-defined magnetization component

    Directory of Open Access Journals (Sweden)

    H. Matsuyama

    2016-03-01

    Full Text Available We developed a micrometer-sized magnetic tip integrated onto the write head of a hard disk drive for spin-polarized scanning tunneling microscopy (SP-STM in the modulated tip magnetization mode. Using SP-STM, we measured a well-defined in-plane spin-component of the tunneling current of the rough surface of a polycrystalline NiFe film. The spin asymmetry of the NiFe film was about 1.3% within the bias voltage range of -3 to 1 V. We obtained the local spin component image of the sample surface, switching the magnetic field of the sample to reverse the sample magnetization during scanning. We also obtained a spin image of the rough surface of a polycrystalline NiFe film evaporated on the recording medium of a hard disk drive.

  9. High-resolution vector magnetometry: Piezo-spin-polarization effect and in-plane strain-induced dominating uniaxial magnetic anisotropy in a 200-nm-thick Ni thin film

    Science.gov (United States)

    Benito, L.

    2018-04-01

    Owing to its high-sensitivity, reliability, fast, versatile and cost-effective operation, vibrating sample magnetometers (VSM) are massively popular characterization instruments at Magnetism laboratories worldwide. Nevertheless, the inherent appearance of synchronous noise represents a major drawback, which critically limits the fine probing of nanometer-sized media. I here report on an innovative approach to eliminate synchronous noise in VSM. This consists of fitting engineered mechanical devices that absorbs vibration energy, dissipating that into heat. Complementarily, a novel transversal pick-up coil system is also presented and analyzed; this detection system has been engineered to enhance the noise-to-signal ratio and optimized for measuring small size thin film samples. The implementation of a combined mechanical and electromagnetic approach enables to notably enhance the VSM performance, achieving a sensitivity better than 1 ×10-6 emu and a resolution below 5 ×10-8 emu, so that the magnetization vector in nanostructured media can be accurately mapped out down to cryogenic temperatures. I lastly show precision magnetometry measurements carried out in an epitaxial (0 0 1)-oriented 200 nm-thick Ni thin film. The analysis reveals the arising of an in-plane dominating strain-induced uniaxial magnetic anisotropy, K2ef = - 6.455kJ m - 3 , and a stunning piezo-spin-polarization effect resulting in a remarkable 10% modulation of the magnetization vector, ∼ 27 emu/cm3, with respect to the cubic lattice axes. Both effects are attributed to the likely existence of an orthorhombic lattice distortion, i.e.εxx -εyy ≈ - 2 ×10-3 . This categorical link enables to assign the observed anisotropic spin-polarization in the Ni overlayer to a two-ion magnetoelastic coupling effect.

  10. Comparison of Electron Transmittance and Tunneling Current through a Trapezoidal Potential Barrier with Spin Polarization Consideration by using Analytical and Numerical Approaches

    Science.gov (United States)

    Nabila, Ezra; Noor, Fatimah A.; Khairurrijal

    2017-07-01

    In this study, we report an analytical calculation of electron transmittance and polarized tunneling current in a single barrier heterostructure of a metal-GaSb-metal by considering the Dresselhaus spin orbit effect. Exponential function, WKB method and Airy function were used in calculating the electron transmittance and tunneling current. A Transfer Matrix Method, as a numerical method, was utilized as the benchmark to evaluate the analytical calculation. It was found that the transmittances calculated under exponential function and Airy function is the same as that calculated under TMM method at low electron energy. However, at high electron energy only the transmittance calculated under Airy function approach is the same as that calculated under TMM method. It was also shown that the transmittances both of spin-up and spin-down conditions increase as the electron energy increases for low energies. Furthermore, the tunneling current decreases with increasing the barrier width.

  11. Adsorption of nitrogen oxides on graphene and graphene oxides: insights from density functional calculations.

    Science.gov (United States)

    Tang, Shaobin; Cao, Zexing

    2011-01-28

    The interactions of nitrogen oxides NO(x) (x = 1,2,3) and N(2)O(4) with graphene and graphene oxides (GOs) were studied by the density functional theory. Optimized geometries, binding energies, and electronic structures of the gas molecule-adsorbed graphene and GO were determined on the basis of first-principles calculations. The adsorption of nitrogen oxides on GO is generally stronger than that on graphene due to the presence of the active defect sites, such as the hydroxyl and carbonyl functional groups and the carbon atom near these groups. These active defect sites increase the binding energies and enhance charge transfers from nitrogen oxides to GO, eventually leading to the chemisorption of gas molecules and the doping character transition from acceptor to donor for NO(2) and NO. The interaction of nitrogen oxides with GO with various functional groups can result in the formation of hydrogen bonds OH⋅⋅⋅O (N) between -OH and nitrogen oxides and new weak covalent bonds C⋅⋅⋅N and C⋅⋅⋅O, as well as the H abstraction to form nitrous acid- and nitric acidlike moieties. The spin-polarized density of states reveals a strong hybridization of frontier orbitals of NO(2) and NO(3) with the electronic states around the Fermi level of GO, and gives rise to the strong acceptor doping by these molecules and remarkable charge transfers from molecules to GO, compared to NO and N(2)O(4) adsorptions on GO. The calculated results show good agreement with experimental observations.

  12. Thermoelectric properties of TbFe{sub 2} and TbCo{sub 2} in C15- laves phase: Spin-polarized DFT+U approach

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, A.H., E-mail: maalidph@yahoo.co.uk [New Technologies - Research Centre, University of West Bohemia, Univerzitni 8, Pilsen 306 14 (Czech Republic); School of Material Engineering, University Malaysia Perlis, Kangar, Perlis 01007 (Malaysia)

    2017-01-15

    Thermoelectric properties of materials are intimately related to their electronic band structure. Combining first- and second-principles calculations, we have obtained the transport properties for the spin-up and spin-down electrons of the laves phase TbFe{sub 2} and TbCo{sub 2} compounds. The unique band structure feature and the density of states at Fermi level (E{sub F}) promote the E{sub F} to a point where carriers are in energetic proximity to these features. The non-zero density of states at E{sub F} for the spin-up (↑) and spin-down (↓) electrons leads to unusual transport properties because both the (↑) and (↓) densities contributes to the states at E{sub F}. The parabolic bands in the vicinity of E{sub F} enhance the carriers mobility and hence the transport properties of TbFe{sub 2} and TbCo{sub 2}. Calculations show that the spin-up/down transport coefficients are temperature-dependent. It has been found that TbCo{sub 2} possess larger Seebeck coefficient than that of TbFe{sub 2} and hence the power factor. The calculated Seebeck coefficient of TbCo{sub 2} agree well with the available experimental data. - Highlights: • The transport properties of TbFe{sub 2} and TbCo{sub 2} are obtained. • The non-zero density of states at E{sub F} leads to unusual transport properties. • Spin-up/down transport coefficients are temperature-dependent. • The calculated Seebeck coefficient of TbCo{sub 2} agree with the experimental data. • TbCo{sub 2} possesses larger Seebeck coefficient than that of TbFe{sub 2}.

  13. Electron spin polarization effects in low-energy electron diffraction, ion neutralization, and metastable-atom deexcitation at solid surfaces. Progress report No. 3, January 1-December 31, 1983

    International Nuclear Information System (INIS)

    Walters, G.K.; Dunning, F.B.

    1983-01-01

    The importance of electron spin polarization (ESP) effects in the various spectroscopies used to study solid surfaces has become increasingly apparent in recent years. Recent low energy electron diffraction (LEED) investigations in this laboratory and elsewhere have shown that a great deal of new information contributing to the understanding of the geometrical arrangements of atoms at a surface can be obtained if the polarization of the various LEED beams is measured, or if the incident electron beam is polarized. Polarized LEED studies have shown large polarization features that are very sensitive to the presence of adsorbed layers, surface reconstruction, etc. In addition, theory suggests that polarization measurements can provide a more sensitive test of many of the parameters used in a surface model than can conventional LEED intensity measurements alone. Polarized LEED has also been applied to the study of surface magnetism. In the present contract year, polarized LEED has been used, together with Auger analysis and LEED intensity measurements, as a diagnostic to characterize Ni(001) surfaces produced by laser annealing

  14. Measurement of thermal accommodation of spin-polarized hydrogen on a saturated 4He film at 0.18--0.4 K

    International Nuclear Information System (INIS)

    Helffrich, J.; Maley, M.P.; Krusius, M.; Wheatley, J.C.

    1986-01-01

    The thermal accommodation of H-gas atoms on a saturated superfluid- 4 He-film-covered surface has been measured in the temperature range 0.18--0.4 K. A straightforward stationary-state measuring technique is employed whereby we determine the heat flux conducted by H-gas atoms from a superfluid- 4 He-film-covered bolometer, biased above ambient temperature. The results agree with recent calculations of the thermal-accommodation properties dominated by sticking-evaporation collisions mediated by ripplon creation

  15. First-principles study of high spin-polarization and thermoelectric efficiency of ferromagnetic CoFeCrAs quaternary Heusler alloy

    Science.gov (United States)

    Bhat, Tahir Mohiuddin; Gupta, Dinesh C.

    2018-03-01

    The ground state properties along with thermodynamic and thermoelectric properties of quaternary CoFeCrAs alloy within the ordered LiMgPdSn-type structure have been investigated by employing first-principles calculations. The alloy offers half-metallic ferromagnet character with an indirect band gap of 1.12 eV in the minority spin state with total spin magnetic moment of 4μB and follows Slater-Pauling relation. Effects on various properties of the material has been studied by the variation of the pressure and temperature. CoFeCrAs tenders large value of the Grüneisen parameter and small value for the thermal expansion coefficient. The materials present high Seebeck coefficient and huge power factor with the room temperature value of ∼-40 μV/K and 18 (1014 μWcm-1 K-2 s-1) respectively, which make CoFeCrAs promising candidate for efficient thermoelectric material.

  16. Spin-polarized current in noncollinear antiferromagnets

    Czech Academy of Sciences Publication Activity Database

    Železný, Jakub; Zhang, Y.; Felser, C.; Yan, B.

    2017-01-01

    Roč. 119, č. 18 (2017), s. 1-7, č. článku 187204. ISSN 0031-9007 Institutional support: RVO:68378271 Keywords : anisotropic magnetoresistance * wannier functions * room-temperature * torques * spintronics Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 8.462, year: 2016

  17. Collective effects in spin polarized plasmas

    International Nuclear Information System (INIS)

    Coppi, B.; Cowley, S.; Detragiache, P.; Kulsrud, R.; Pegoraro, F.

    1984-10-01

    A fusing plasma with coherently polarized spin nuclei can be subject to instabilities due to the anisotropy of the reaction product distributions in velocity space, which is a result of their polarization. The characteristics of these instabilities depend strongly on the plasma spatial inhomogeneities and a significant rate of spin depolarization can be produced by them if adequate fluctuation amplitudes are reached. The results of the relevant analysis are, in addition, of interest for plasma heating processes with frequencies in the range of the cyclotron frequencies of the considered nuclei

  18. Photoinduced spin polarization and microwave technology

    International Nuclear Information System (INIS)

    Antipov, Sergey; Poluektov, Oleg; Schoessow, Paul; Kanareykin, Alexei; Jing, Chunguang

    2013-01-01

    We report here on studies of optically pumped active microwave media based on various fullerene derivatives, with an emphasis on the use of these materials in microwave electronics. We have investigated a class of optically excited paramagnetic materials that demonstrate activity in the X-band as candidate materials. We found that a particular fullerene derivative, Phenyl-C 61 -butyric acid methyl ester (PCBM), produced the largest electron paramagnetic resonance (EPR) emission signal compared to other organic compounds that have been suggested for use as microwave active materials. We also studied the effects of concentration, temperature, solvent etc. on the activity of the material. In these experiments, EPR studies using a commercial spectrometer were followed up by measurements of an RF signal reflected from a resonator loaded with the PCBM-based material. The activity was directly demonstrated through the change in the quality factor and RF coupling between the resonator and waveguide feed. At the inception of these experiments the primary interest was the development of a microwave PASER. The PASER (particle acceleration by stimulated emission of radiation [1]) is a novel acceleration concept that is based on the direct energy transfer from an active medium to a charged particle beam. While the previous work on the PASER has emphasized operations at infrared or visible wavelengths, operating in the microwave regime has significant advantages in terms of the less stringent quality requirements placed on the electron beam provided an appropriate microwave active medium can be found. This paper is focused on our investigation of the possibility of a PASER operating in the microwave frequency regime [2] using active paramagnetic materials. While a high level of gain for PCBM was demonstrated compared to other candidate materials, dielectric losses and quenching effects were found to negatively impact its performance for PASER applications. We present results on development and bench testing for these new fullerene-based materials along with some conceptual designs for microwave PASERs. Other possible applications for active paramagnetic materials are suggested including low noise microwave amplifiers and tunable RF absorbers.

  19. Spin polarization in high density quark matter

    DEFF Research Database (Denmark)

    Bohr, Henrik; Panda, Prafulla K.; Providênci, Constanca

    2013-01-01

    We investigate the occurrence of a ferromagnetic phase transition in high density hadronic matter (e.g., in the interior of a neutron star). This could be induced by a four-fermion interaction analogous to the one which is responsible for chiral symmetry breaking in the Nambu-Jona-Lasinio model...... the so-called 2 flavor super-conducting phase to the ferromagnetic phase arises. The color-flavor-locked phase may be completely hidden by the FP....

  20. Burnout calculation

    International Nuclear Information System (INIS)

    Li, D.

    1980-01-01

    Reviewed is the effect of heat flux of different system parameters on critical density in order to give an initial view on the value of several parameters. A thorough analysis of different equations is carried out to calculate burnout is steam-water flows in uniformly heated tubes, annular, and rectangular channels and rod bundles. Effect of heat flux density distribution and flux twisting on burnout and storage determination according to burnout are commended [ru

  1. The New Planned Giving Officer.

    Science.gov (United States)

    Jordan, Ronald R.; Quynn, Katelyn L.

    1994-01-01

    A planned giving officer is seen as an asset to college/university development for technical expertise, credibility, and connections. Attorneys, certified public accountants, bank trust officers, financial planners, investment advisers, life insurance agents, and real estate brokers may be qualified but probably also need training. (MSE)

  2. Analysis gives sensibility two models gives migration and transport gives radionuclides in the geosphere

    International Nuclear Information System (INIS)

    Torres Berdeguez, M. B.; Gil Castillo, R.; Peralta Vidal, J.L.

    1998-01-01

    An sensibility analysis it was applied two models, the first one, a model compressible for the near field (I finish source) The second, a simple model gives migration and transport radionuclides in the geosphere. The study was developed varying the securities ed simultaneously at the same time each parameter and observing the results in changes in the output and input. The intention in analysis it is to determine the parameter that but it influences in the variation the concentration. The statistical technique Regression it was employee in the study. This statistical method is used to analyze the dependence between a dependent variable and an or but independent variables

  3. Energy gap of extended states in SiC-doped graphene nanoribbon: Ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiaoshi; Wu, Yong [College of Science, University of Shanghai for Science and Technology, Shanghai 200093 (China); Shanghai Key Lab of Modern Optical System, Shanghai 200093 (China); Li, Zhongyao, E-mail: lizyusst@gmail.com [College of Science, University of Shanghai for Science and Technology, Shanghai 200093 (China); Shanghai Key Lab of Modern Optical System, Shanghai 200093 (China); Gao, Yong [School of Science, Shanghai Second Polytechnic University, Shanghai 201209 (China)

    2017-04-01

    Highlights: • The gap of isolated ribbon is inversely proportional to the width of ribbon. • The gap of doped ribbon cannot be modeled by effective width approximation. • The fitted energy gap can match the experimental observations. • The doping results in a spin-polarized metallic-like band structure. - Abstract: The energy gap of extended states in zigzag graphene nanoribbons (ZGNRs) was examined on the basis of density-functional theory. In isolated ZGNRs, the energy gap is inversely proportional to the width of ribbon. It agrees well with the results from the Dirac equation in spin-unpolarized ZGNRs, although the considered ZGNRs have spin-polarized edges. However, the energy gap in SiC-doped ZGNRs cannot be modeled by effective width approximation. The doping also lifts the spin-degenerate of edge states and results in a metallic-like band structure near the Fermi level in SiC-doped ZGNRs. Our calculations may be helpful for understanding the origin of the reported single-channel ballistic transport in epitaxial graphene nanoribbons.

  4. Magnetic and electronic properties of Cu1-xFexO from first principles calculations

    KAUST Repository

    Yang, Hua

    2013-01-01

    Magnetic and electronic properties of Cu1-xFexO systems with x = 6.25% and 12.5% have been investigated using first principles calculations. The ground state of CuO is an antiferromagnetic insulator. At x = 6.25%, Cu1-xFexO systems with Fe on 2 and 4 substitution positions are half-metallic due to the strong hybridization among Fe, the nearest O and Cu atoms, which may come from the double exchange coupling between Fe2+-O2--Cu2+. At x = 12.5%, Cu 1-xFexO system with Fe on 9-11 position has a strong spin polarization near the Fermi level and the system energy is lowest when the doped two Fe atoms form ferromagnetic configuration. This indicates the two doped Fe atoms prefer to form ferromagnetic configuration in Fe2+-O 2--Cu2+-O2--Fe2+ chains. While in the Fe on 7-11 position, the spin-down Fe-11 3d states have a large spin polarization near the Fermi level when the two doped Fe atoms form antiferromagnetic configuration. It is concluded that the transition metal doping can modify the magnetism and electronic structures of Cu 1-xFexO systems. This journal is © The Royal Society of Chemistry 2013.

  5. To give or not to give, that's the question: How methodology is destiny in Dutch giving data

    NARCIS (Netherlands)

    Bekkers, R.H.F.P.; Wiepking, P.

    2006-01-01

    In research on giving, methodology is destiny. The volume of donations estimated from sample surveys strongly depends on the length of the questionnaire used to measure giving. By comparing two giving surveys from the Netherlands, the authors show that a short questionnaire on giving not only

  6. To Give or Not to Give, That Is the Question : How Methodology Is Destiny in Dutch Giving Data

    NARCIS (Netherlands)

    Bekkers, René; Wiepking, Pamala

    2006-01-01

    In research on giving, methodology is destiny. The volume of donations estimated from sample surveys strongly depends on the length of the questionnaire used to measure giving. By comparing two giving surveys from the Netherlands, the authors show that a short questionnaire on giving not only

  7. First-principles calculations on Fe-Pt nanoclusters of various morphologies.

    Science.gov (United States)

    Platonenko, Alexander; Piskunov, Sergei; Bocharov, Dmitry; Zhukovskii, Yuri F; Evarestov, Robert A; Bellucci, Stefano

    2017-09-05

    Bimetallic FePt nanoparticles with L1 0 structure are attracting a lot of attention due to their high magnetocrystalline anisotropy and high coercivity what makes them potential material for storage of ultra-high density magnetic data. FePt nanoclusters are considered also as nanocatalysts for growth of carbon nanotubes of different chiralities. Using the DFT-LCAO CRYSTAL14 code, we have performed large-scale spin-polarized calculations on 19 different polyhedral structures of FePt nanoparticles in order to estimate which icosahedral or hcp-structured morphology is the energetically more preferable. Surface energy calculations of all aforementioned nanoparticles indicate that the global minimum corresponds to the nanocluster possessing the icosahedron "onion-like" structure and Fe 43 Pt 104 morphology where the outer layer consists of Pt atoms. The presence of the Pt-enriched layer around FePt core explains high oxidation resistance and environmental stability, both observed experimentally.

  8. Elastic properties of Ni2MnGa from first-principles calculations

    International Nuclear Information System (INIS)

    Ozdemir Kart, S.; Cagin, T.

    2010-01-01

    Research highlights: In this study, we have performed spin-polarized total energy calculations aiming to develop microscopic understanding of magnetic shape memory behavior of Ni 2 MnGa. This paper is devoted to determine the mechanical properties of Ni 2 MnGa in both austenitic and martensitic structures. To the best of our knowledge, this work presents the elastic constants of Ni 2 MnGa in the structure of 5M martensite, for the first time. We have also re-calculated elastic constants for cubic and nonmodulated (NM) structures by using the potential with e/a = 7.5. The elastic constants are predicted by straining the cubic L2 1 , 5M pseudo-tetragonal and NM tetragonal martensitic structures. Because of the special significance of the isotropic bulk modulus, shear modulus, Young's modulus and Poisson's ratio for technological applications, we have also calculated these quantities from the elastic constants. - Abstract: Elastic properties of Ni 2 MnGa in both austenitic and martensitic structures are determined by using ab initio methods based on density functional theory (DFT) within the spin-polarized generalized-gradient approximation. The tetragonal shear elastic constant C' takes a very small value in the austenitic phase, indicating the elastic instability results in a phase transition to martensitic structure. Isotropic mechanical properties such as bulk modulus, shear modulus, Young's modulus and Poisson's ratio are predicted. The trend of the Debye temperatures calculated for three structures of Ni 2 MnGa is comparable with that of the experiment.

  9. Calculator calculus

    CERN Document Server

    McCarty, George

    1982-01-01

    How THIS BOOK DIFFERS This book is about the calculus. What distinguishes it, however, from other books is that it uses the pocket calculator to illustrate the theory. A computation that requires hours of labor when done by hand with tables is quite inappropriate as an example or exercise in a beginning calculus course. But that same computation can become a delicate illustration of the theory when the student does it in seconds on his calculator. t Furthermore, the student's own personal involvement and easy accomplishment give hi~ reassurance and en­ couragement. The machine is like a microscope, and its magnification is a hundred millionfold. We shall be interested in limits, and no stage of numerical approximation proves anything about the limit. However, the derivative of fex) = 67.SgX, for instance, acquires real meaning when a student first appreciates its values as numbers, as limits of 10 100 1000 t A quick example is 1.1 , 1.01 , 1.001 , •••• Another example is t = 0.1, 0.01, in the functio...

  10. Know Concentration Before Giving Acetaminophen to Infants

    Science.gov (United States)

    ... For Consumers Home For Consumers Consumer Updates Know Concentration Before Giving Acetaminophen to Infants Share Tweet Linkedin ... infants has only been available in a stronger concentration that doesn’t require giving the infants as ...

  11. Income Tax Policy and Charitable Giving

    Science.gov (United States)

    Brooks, Arthur C.

    2007-01-01

    Many studies over the past 20 years have looked at the response of charitable donations to tax incentives--the tax price elasticity of giving. Generally, authors have assumed this elasticity is constant across all types of giving. Using the 2001 Panel Study of Income Dynamics data on charitable giving, this paper estimates the tax price elasticity…

  12. Mensurations give the radioactivity natural gamma, radon in Chile

    International Nuclear Information System (INIS)

    Gamarra, J.; Stuardo, E.

    1998-01-01

    In this work, are presented the methods for measurement, calculate and you discusses the results, in each studied area, in the mark the respective world averages. None the averages evaluated annual effective dose they surpassed these world averages effective dose or level gives intervention, corresponding

  13. The Practical Realities of Giving Back

    Directory of Open Access Journals (Sweden)

    Ashton Bree Wesner

    2014-07-01

    Full Text Available In this thematic section, authors consider practical ways of giving back to the communities in which they conduct research. Each author discusses their evolving thoughts on how to give back in these practical ways. Some of these authors discuss giving back by giving money, food, rides, parties, and water bottles. In other cases, authors discuss giving back by creating jobs in the short or long term, grant writing, advocacy, and education. Story-telling is also a theme that many of the authors in this section discuss. For some authors, non-material forms of giving back are critical—simply maintaining social ties to the communities in which they worked, or sharing humor. The authors consider the utility of their attempts at giving back, and in some cases present their personal philosophy or guidelines on the subject.

  14. Ab initio calculations of elastic and magnetic properties of Fe, Co, Ni, and Cr crystals under isotropic deformation

    Science.gov (United States)

    Černý, M.; Pokluda, J.; Šob, M.; Friák, M.; Šandera, P.

    2003-01-01

    Ab initio electronic structure calculations of the ideal strength of Fe, Co, Ni, and Cr under isotropic tension were performed using the linear muffin-tin orbital method in the atomic sphere approximation. Magnetic ordering was taken into account by means of a spin-polarized calculation. Two approximations for the exchange-correlation term were employed: namely, the local (spin) density approximation and the generalized gradient approximation. Computed values of equilibrium lattice parameters, bulk moduli, and magnetic moments were compared with available experimental data. The stability of the ground-state structure in the tensile region was assessed via comparison of its total energy and enthalpy with those of some other structures. No instabilities were found before reaching the inflection point on the total energy versus volume curve and the stress related to this point was therefore considered to be the ideal strength.

  15. Mapping the imaginary of charitable giving

    DEFF Research Database (Denmark)

    Bajde, Domen

    2012-01-01

    The meaningfulness of charitable giving is largely owed to the imaginary conceptions that underpin this form of giving. Building on Taylor's notion of “social imaginary” and Godelier's work on “gift imaginary,” we theorize the imaginary of charitable giving. Through a combination of qualitative m...... across relatively stable assemblages of conceptions of poverty, donors, end-recipients and charitable giving. These assemblages are suggested to form a multifaceted imaginary that is both cultural (shared) and personal (individually performed)....... methods the charitable gift imaginary and its role in givers' meaning making are explored in a specific socio-cultural context. The theoretical foundation and the generated data enable us to map the imaginary of charitable giving across four distinct clusters and theorize meaning – making as navigation...

  16. George Stephanopoulos to give Cutchins Distinguished Lecture

    OpenAIRE

    Ho, Sookhan

    2006-01-01

    ABC News' chief Washington correspondent and"This Week" anchor George Stephanopoulos will give the Cutchins Distinguished Lecture at Virginia Tech on Thursday, March 16, 7:30 p.m., in Burruss Auditorium.

  17. Washington. Will Tax Reform Affect Giving?

    Science.gov (United States)

    Myers, John Holt

    1974-01-01

    Examines considerations of tax reform and their impact on the ability of colleges and universities to attract private giving, frequently making the difference between institutional death and survival. (Author/PG)

  18. System for the chemical professing and evaluation gives the residual thickness the gives detecting for gives appearances LR115 type 2

    International Nuclear Information System (INIS)

    Carrazana Gonzalez, J.A.; Tomas Zerquera, J.; Prendes Alonso, M.

    1998-01-01

    In this work the system is described built in the CPHR for the homogeneous chemical processing gives detecting gives nuclear appearances. A new developed method is exposed, based on the application gives the technique optical densitometry, for the precise estimate gives the residual thickness, gives detecting, gives nuclear appearances LR115 type 2 after the process gives chemical engraving

  19. Testing for altruism and social pressure in charitable giving.

    Science.gov (United States)

    DellaVigna, Stefano; List, John A; Malmendier, Ulrike

    2012-01-01

    Every year, 90% of Americans give money to charities. Is such generosity necessarily welfare enhancing for the giver? We present a theoretical framework that distinguishes two types of motivation: individuals like to give, for example, due to altruism or warm glow, and individuals would rather not give but dislike saying no, for example, due to social pressure. We design a door-to-door fund-raiser in which some households are informed about the exact time of solicitation with a flyer on their doorknobs. Thus, they can seek or avoid the fund-raiser. We find that the flyer reduces the share of households opening the door by 9% to 25% and, if the flyer allows checking a Do Not Disturb box, reduces giving by 28% to 42%. The latter decrease is concentrated among donations smaller than $10. These findings suggest that social pressure is an important determinant of door-to-door giving. Combining data from this and a complementary field experiment, we structurally estimate the model. The estimated social pressure cost of saying no to a solicitor is $3.80 for an in-state charity and $1.40 for an out-of-state charity. Our welfare calculations suggest that our door-to-door fund-raising campaigns on average lower the utility of the potential donors.

  20. The Effect of Media on Charitable Giving and Volunteering: Evidence from the "Give Five" Campaign

    Science.gov (United States)

    Yoruk, Baris K.

    2012-01-01

    Fundraising campaigns advertised via mass media are common. To what extent such campaigns affect charitable behavior is mostly unknown, however. Using giving and volunteering surveys conducted biennially from 1988 to 1996, I investigate the effect of a national fundraising campaign, "Give Five," on charitable giving and volunteering patterns. The…

  1. First principle calculations of structural, electronic and magnetic properties of cubic GdCrO3 Perovskite

    Science.gov (United States)

    Terkhi, Sabria; Bentata, Samir; Aziz, Zoubir; Lantri, Tayeb; Abbar, Boucif

    2018-02-01

    The structural, electronic and magnetic properties of the cubic GdCrO3 perovskite are investigated by mean the full-potential linearized augmented plane wave method based on the density functional theory. We have used three approximations: the generalized gradient (GGA), the GGA + U, where U is on-site Coulomb interaction correction, and the modified Becke-Johnson (mBJ-GGA). Calculated Lattice parameters are where found to be in a very good agreement with experimental measurements. Our results of spin-polarized band structure and density of states show a metallic character of GdCrO3 when using the GGA scheme, whereas a half-metallic ferromagnetic behavior is observed in both cases of GGA + U and mBJ-GGA approaches with an important total magnetic moment of 10.00 μB. The obtained results show that GdCrO3 is an excellent candidate to spintronic applications.

  2. Calculation of Half-Metal, Debye and Curie Temperatures of Co2VAl Compound: First Principles Study

    Science.gov (United States)

    Arash, Boochani; Heidar, Khosravi; Jabbar, Khodadadi; Shahram, Solaymani; Masoud Majidiyan, Sarmazdeh; Rohollah Taghavi, Mendi; Sayed, Mohammad Elahi

    2015-05-01

    By FP-LAPW calculations, the structural, elastic, Debye and Curie temperatures, electronic and magnetic properties of Co2 VAl are investigated. The results indicate that Ferromagnetic (FM) phase is more stable than Anti-Ferromagnetic (AFM) and Non-magnetic (NM) ones. In addition, C11-C12 > 0, C44 > 0, and B > 0 so Co2VAl is an elastically stable material with high Debye temperature. Also, the B/G ratio exhibits a ductility behavior. The relatively high Curie temperature provides it as a favorable material for spintronic application. It's electronic and magnetic properties are studied by GGA+U approach leading to a 100% spin polarization at Fermi level. Supported by the simulation of Nano Physics Lab center of Kermanshah Branch, Islamic Azad University

  3. Role of anion doping on electronic structure and magnetism of GdN by first principles calculations

    KAUST Repository

    Zhang, Xuejing

    2014-01-01

    We have investigated the electronic structure and magnetism of anion doped GdN1-yXy (X = B, C, O, F, P, S and As) systems by first-principles calculations based on density functional theory. GdN 1-yXy systems doped by O, C, F, P, and S atoms are more stable than those doped by B and As atoms because of relatively high binding energies. The anion doping and the N defect states modify the density of states at the Fermi level, resulting in a decrease in spin polarization and a slight increase in the magnetic moment at the Gd and N sites. © 2014 The Royal Society of Chemistry.

  4. The Luxury of Igniting Change by Giving

    DEFF Research Database (Denmark)

    Llamas, Rosa; Uth Thomsen, Thyra

    2016-01-01

    of distant others by giving them valuable philanthropic gifts and thereby ultimately transforming the self of the giver. The paper shows how giving away economic capital (money and time), social capital (networks and influence), and cultural capital (skills and knowledge) to non-related others can provide...... the giver with a sense of luxury in terms of pleasure, purpose, and connection with humankind. Thus, the findings not only extend the traditional conceptualization of luxury from having to giving, but also challenge current conceptualizations of sharing out as a non-reciprocal pro-social behavior......This study investigates the phenomenon of luxury from a consumer perspective, by means of multisited phenomenological inquiry. The findings expand the pervasive view of luxury as accumulation of highly valued goods by offering a transformative perspective of luxury as transforming the life...

  5. Declination Calculator

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Declination is calculated using the current International Geomagnetic Reference Field (IGRF) model. Declination is calculated using the current World Magnetic Model...

  6. They Make Space and Give Time

    Indian Academy of Sciences (India)

    ... Resonance – Journal of Science Education; Volume 3; Issue 3. They Make Space and Give Time The Engineer as Poet. Gangan Prathap. Book Review Volume 3 ... Author Affiliations. Gangan Prathap1. National Aerospace Laboratories and the Jawaharlal Nehru Centre for Advanced Scientific Research in Bangalore.

  7. Termination of Commercial Contracts by giving Notice

    DEFF Research Database (Denmark)

    Edlund, Hans Henrik

    2008-01-01

    Some long-term contracts are brought to an end if one of the parties gives notice. Usually, such a step is not considered a breach of contract. It causes the contract to end in accordance with the contract. When no express rules cover the situation, it is often not entirely clear whether or not t...

  8. Give and Take in Dictator Games

    DEFF Research Database (Denmark)

    Cappelen, Alexander W.; Nielsen, Ulrik Haagen; Sørensen, Erik Ø.

    2014-01-01

    It has been shown that participants in the dictator game are less willing to give money to the other participant when their choice set also includes the option to take money. We examine whether this effect is due to the choice set providing a signal about entitlements in a setting where...

  9. Asian American Giving to US Higher Education

    Science.gov (United States)

    Tsunoda, Kozue

    2010-01-01

    Asian Americans have had significant impacts on and within mainstream US society, and their great efforts and gifts in the name of charitable causes are no exception. This study aims to examine perceptions within American university development offices about Asian American giving to US higher education. The article begins with a literature review…

  10. Seeds That Give: Participatory Plant Breeding

    International Development Research Centre (IDRC) Digital Library (Canada)

    in_focus. Seeds that give. PARTICIPATORY PLANT BREEDING. in_focus. IDRC's In_Focus Collection tackles current and pressing issues in sustainable international development. Each publication distills IDRC's research experience with an eye to drawing out important lessons, observations, and recommendations for ...

  11. Giving advice to agents with hidden goals

    CSIR Research Space (South Africa)

    Rosman, Benjamin S

    2014-05-01

    Full Text Available on an approximation of the trade-off in utility between potential benefits to the exploring agent and the costs incurred in giving this advice. This model is evaluated on a maze world domain by providing advice to different types of agents, and we show that this leads...

  12. The Costs and Benefits of Deferred Giving.

    Science.gov (United States)

    Fink, Norman S.; Metzler, Howard C.

    It is argued in this book that while there can be a significant payoff for deferred giving programs, it is important to determine their cost effectiveness. Modern business methods of cost accounting, benefits analysis, and actuarial and econometric forecasting are applied to the Pomona College plan, whose study was supported by Lilly Endowment,…

  13. SEEDS THAT GIVE: Participatory Plant Breeding

    International Development Research Centre (IDRC) Digital Library (Canada)

    IDRC

    each other, and pay close attention to what the farmers told you? Revolutionary perhaps, but it's a revolution that has produced positive results. 1. Case study. Seeds. PARTICIPATORY PLANT BREEDING that give. ICARDA: S. Ceccarelli. Working together, researchers, farmers, breeders, and social scientists are increasing ...

  14. Seeds that give: Participatory plant breeding

    International Development Research Centre (IDRC) Digital Library (Canada)

    IDRC

    Sometimes when we plant and we expect good results, we actually get poor results. And sometimes it is the other way around. But I can't just discard a variety because it doesn't perform well in one area. I should give it another chance.”.

  15. Intergenerational Transmission of Religious Giving: Instilling Giving Habits across the Life Course

    Directory of Open Access Journals (Sweden)

    Patricia Snell Herzog

    2016-07-01

    Full Text Available This paper investigates the research question: How do religious youth learn to give? While it is likely that youth learn religious financial giving from a variety of different sources, this investigation focuses primarily on how parents teach giving to their children. Supplementary data are also analyzed on the frequency in which youth hear extra-familial calls to give within their religious congregations. In focusing on parental transmission, the analysis identifies a number of approaches that parents report using to teach their children religious financial giving. It also investigates thoughts and feelings about religious financial giving by the children of these parents as a means of assessing the potential impacts of parental methods. Additionally, congregation member reflections on how they learned to give provide insights on giving as a process that develops across the life course, often instilled in childhood, but not appearing behaviorally until adulthood. As such, this paper contributes to a life course understanding of religious giving and has implications for giving across generations.

  16. Role-modeling and conversations about giving in the socialization of adolescent charitable giving and volunteering.

    Science.gov (United States)

    Ottoni-Wilhelm, Mark; Estell, David B; Perdue, Neil H

    2014-01-01

    This study investigated the relationship between the monetary giving and volunteering behavior of adolescents and the role-modeling and conversations about giving provided by their parents. The participants are a large nationally-representative sample of 12-18 year-olds from the Panel Study of Income Dynamics' Child Development Supplement (n = 1244). Adolescents reported whether they gave money and whether they volunteered. In a separate interview parents reported whether they talked to their adolescent about giving. In a third interview, parents reported whether they gave money and volunteered. The results show that both role-modeling and conversations about giving are strongly related to adolescents' giving and volunteering. Knowing that both role-modeling and conversation are strongly related to adolescents' giving and volunteering suggests an often over-looked way for practitioners and policy-makers to nurture giving and volunteering among adults: start earlier, during adolescence, by guiding parents in their role-modeling of, and conversations about, charitable giving and volunteering. Copyright © 2013 The Foundation for Professionals in Services for Adolescents. Published by Elsevier Ltd. All rights reserved.

  17. Bolus calculators.

    Science.gov (United States)

    Schmidt, Signe; Nørgaard, Kirsten

    2014-09-01

    Matching meal insulin to carbohydrate intake, blood glucose, and activity level is recommended in type 1 diabetes management. Calculating an appropriate insulin bolus size several times per day is, however, challenging and resource demanding. Accordingly, there is a need for bolus calculators to support patients in insulin treatment decisions. Currently, bolus calculators are available integrated in insulin pumps, as stand-alone devices and in the form of software applications that can be downloaded to, for example, smartphones. Functionality and complexity of bolus calculators vary greatly, and the few handfuls of published bolus calculator studies are heterogeneous with regard to study design, intervention, duration, and outcome measures. Furthermore, many factors unrelated to the specific device affect outcomes from bolus calculator use and therefore bolus calculator study comparisons should be conducted cautiously. Despite these reservations, there seems to be increasing evidence that bolus calculators may improve glycemic control and treatment satisfaction in patients who use the devices actively and as intended. © 2014 Diabetes Technology Society.

  18. The influence of stress on giving testimony

    Directory of Open Access Journals (Sweden)

    Brkić Snežana S.

    2015-01-01

    Full Text Available In this paper there are firstly some general observations about stress (the concept of stress, stressors, stress responses, consequences of stress. Then, the author examines the effect of stress on giving testimony, that is on two most important psychic functions of the importance for giving testimony: perception and memory. The impact of stress, on perception is discussed in the framework of the importance of affective tone of perception. The lower doses of stress can improve attention and perception, but with intense stress, attention rapidly decreases. Stress often causes erroneous perception of time and other errors in observation and can lead to illusions and hallucinations. The errors in face recognition are also possible in view of 'the phenomenon of focusing attention on weapon '. In relationship with memory, the author firstly gives some general considerations about this function. Then follows brief overview of memory for emotionally colored events. The negative influence of stress on memory is reflected in the possibility of psychogenic amnesia, which are often the escort of psychological trauma. Further, some events will be remembered with a lot of gaps, distortions and overemphasis. The paper points to a number of studies on (inaccuracies and (incomplete memories for traumatic events. Summarizing the main results of these studies it is concluded that memory for traumatic events has similar sharacteristics as memory for normal, nontraumatic events. Memory for traumatic events also follows the same cognitive principles. In that sense, both traumatic and nontraumatic memories can be equally powerful on the one hand, and on the other hand, there may be gaps or errors in memory as well as for the positive and negative life events.

  19. Daylight calculations in practice

    DEFF Research Database (Denmark)

    Iversen, Anne; Roy, Nicolas; Hvass, Mette

    programs can give different results. This can be due to restrictions in the program itself and/or be due to the skills of the persons setting up the models. This is crucial as daylight calculations are used to document that the demands and recommendations to daylight levels outlined by building authorities....... The aim of the project was to obtain a better understanding of what daylight calculations show and also to gain knowledge of how the different daylight simulation programs perform compared with each other. Furthermore the aim was to provide knowledge of how to build up the 3D models that were...

  20. Lattice cell burnup calculation

    International Nuclear Information System (INIS)

    Pop-Jordanov, J.

    1977-01-01

    Accurate burnup prediction is a key item for design and operation of a power reactor. It should supply information on isotopic changes at each point in the reactor core and the consequences of these changes on the reactivity, power distribution, kinetic characters, control rod patterns, fuel cycles and operating strategy. A basic stage in the burnup prediction is the lattice cell burnup calculation. This series of lectures attempts to give a review of the general principles and calculational methods developed and applied in this area of burnup physics

  1. Giving Ourselves Permission to Take Risks

    Science.gov (United States)

    Jones, Elizabeth

    2012-01-01

    What's a risk? It's when one doesn't know what will happen when she/he takes action. Risks can be little or big, calculated or stupid. Every new idea carries risks--and the challenge to face them and see what will happen. Nobody becomes smart, creative, self-confident, and respectful of others without taking risks--remaining open to possibilities…

  2. MEMS Calculator

    Science.gov (United States)

    SRD 166 MEMS Calculator (Web, free access)   This MEMS Calculator determines the following thin film properties from data taken with an optical interferometer or comparable instrument: a) residual strain from fixed-fixed beams, b) strain gradient from cantilevers, c) step heights or thicknesses from step-height test structures, and d) in-plane lengths or deflections. Then, residual stress and stress gradient calculations can be made after an optical vibrometer or comparable instrument is used to obtain Young's modulus from resonating cantilevers or fixed-fixed beams. In addition, wafer bond strength is determined from micro-chevron test structures using a material test machine.

  3. Calculation of the expected zero-field muon relaxation rate in the geometrically frustrated rare earth pyrochlore Gd(2)Sn(2)O(7) antiferromagnet.

    Science.gov (United States)

    McClarty, P A; Cosman, J N; Del Maestro, A G; Gingras, M J P

    2011-04-27

    The magnetic insulator Gd(2)Sn(2)O(7) is one of many geometrically frustrated magnetic materials known to exhibit a nonzero muon spin polarization relaxation rate, λ(T), down to the lowest temperature (T) studied. Such behaviour is typically interpreted as signalling the presence of persistent spin dynamics (PSD) of the host material. In the case of Gd(2)Sn(2)O(7), such PSD comes as a surprise since magnetic specific heat measurements suggest conventional gapped magnons, which would naively lead to an exponentially vanishing λ(T) as T → 0. In contrast to most materials that display PSD, the ordered phase of Gd(2)Sn(2)O(7) is well characterized and both the nature and the magnitude of the interactions have been inferred from the magnetic structure and the temperature dependence of the magnetic specific heat. Based on this understanding, the temperature dependence of the muon spin polarization relaxation through the scattering of spin waves (magnons) is calculated. The result explicitly shows that, despite the unusual extensive number of weakly dispersive (gapped) excitations characterizing Gd(2)Sn(2)O(7), a remnant of the zero modes of the parent frustrated pyrochlore Heisenberg antiferromagnet, the temperature dependence of the calculated λ(T) differs dramatically from the experimental one. Indeed, the calculation conforms to the naive expectation of an exponential collapse of λ(T) at temperatures below ∼ 0.7 K. This result, for the first time, illustrates crisply and quantitatively the paradox that presents itself with the pervasive occurrence of PSD in highly frustrated magnetic systems as evinced by muon spin relaxation measurements.

  4. Compact scanning tunneling microscope for spin polarization measurements.

    Science.gov (United States)

    Kim, Seong Heon; de Lozanne, Alex

    2012-10-01

    We present a design for a scanning tunneling microscope that operates in ultrahigh vacuum down to liquid helium temperatures in magnetic fields up to 8 T. The main design philosophy is to keep everything compact in order to minimize the consumption of cryogens for initial cool-down and for extended operation. In order to achieve this, new ideas were implemented in the design of the microscope body, dewars, vacuum chamber, manipulators, support frame, and vibration isolation. After a brief description of these designs, the results of initial tests are presented.

  5. Light-induced spin polarizations in quantum rings

    NARCIS (Netherlands)

    Joibari, F.K.; Blanter, Y.M.; Bauer, G.E.W.

    2014-01-01

    Nonresonant circularly polarized electromagnetic radiation can exert torques on magnetizations by the inverse Faraday effect (IFE). Here, we discuss the enhancement of IFE by spin-orbit interactions. We illustrate the principle by studying a simple generic model system, i.e., the

  6. Role of spin polarized tunneling in magnetoresistance and low ...

    Indian Academy of Sciences (India)

    Lowering of ρ0 value (table 2) on application of magnetic field suggests that such imperfections are .... Soma Das and T K Dey. 636. Table 3. Best-fit parameters obtained from intergranular tun- neling model. H ρ0 ρ1 × 105. JS/KB. (Tesla). (Ω cm). (Ω cm K–3/2) ε. (K) x = 0⋅05. 0. 0⋅0731. 6⋅00. 0⋅4175. 95⋅61. 0⋅8.

  7. In1-xMnxSb: spin polarization, conductivity

    Science.gov (United States)

    Matsukura, F.

    This document is part of Subvolume D 'New Data and Updates for IV-IV; III-V; II-VI and I-VII Compounds; their Mixed Crystals and Diluted Magnetic Semiconductors' of Volume 44 'Semiconductors' of Landolt-Börnstein - Group III 'Condensed Matter'.

  8. Role of spin polarized tunneling in magnetoresistance and low ...

    Indian Academy of Sciences (India)

    KMnO3 has been investigated between 10 K and 300 K with and without the magnetic field ( = 0.8 T). All the samples show metal–insulator transitions with Curie temperature (C) ranging between 260 K and 309 K. At temperature below 60 ...

  9. Spin polarization of electrons in a magnetic impurity doped ...

    Indian Academy of Sciences (India)

    The spin of electrons in semiconductors strongly couple with electric and magnetic fields due to ... where ckμ and d−kμ are annihilation operators for electron with momentum k and spin μ and hole with momentum −k ... kμ and ekμ are annihilation and creation operators for impurity electrons. Qkμ and Qkμ are the coefficient ...

  10. Spin-polarized quantum transport properties through flexible phosphorene

    Science.gov (United States)

    Chen, Mingyan; Yu, Zhizhou; Xie, Yiqun; Wang, Yin

    2016-10-01

    We report a first-principles study on the tunnel magnetoresistance (TMR) and spin-injection efficiency (SIE) through phosphorene with nickel electrodes under the mechanical tension and bending on the phosphorene region. Both the TMR and SIE are largely improved under these mechanical deformations. For the uniaxial tension (ɛy) varying from 0% to 15% applied along the armchair transport (y-)direction of the phosphorene, the TMR ratio is enhanced with a maximum of 107% at ɛy = 10%, while the SIE increases monotonously from 8% up to 43% with the increasing of the strain. Under the out-of-plane bending, the TMR overall increases from 7% to 50% within the bending ratio of 0%-3.9%, and meanwhile the SIE is largely improved to around 70%, as compared to that (30%) of the flat phosphorene. Such behaviors of the TMR and SIE are mainly affected by the transmission of spin-up electrons in the parallel configuration, which is highly dependent on the applied mechanical tension and bending. Our results indicate that the phosphorene based tunnel junctions have promising applications in flexible electronics.

  11. Still Giving Thanks for Good Health

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] Click on the image for Still Giving Thanks for Good Health (QTVR) NASA's Mars Exploration Rover Spirit took this full-circle panorama of the region near 'Husband Hill' (the peak just to the left of center) over the Thanksgiving holiday, before ascending farther. Both the Spirit and Opportunity rovers are still going strong, more than a year after landing on Mars. This 360-degree view combines 243 images taken by Spirit's panoramic camera over several martian days, or sols, from sol 318 (Nov. 24, 2004) to sol 325 (Dec. 2, 2004). It is an approximately true-color rendering generated from images taken through the camera's 750-, 530-, and 480-nanometer filters. The view is presented here in a cylindrical projection with geometric seam correction. Spirit is now driving up the slope of Husband Hill along a path about one-quarter of the way from the left side of this mosaic.

  12. Giving Devices the Ability to Exercise Reason

    Directory of Open Access Journals (Sweden)

    Thomas Keeley

    2008-10-01

    Full Text Available One of the capabilities that separates humans from computers has been the ability to exercise "reason / judgment". Computers and computerized devices have provided excellent platforms for following rules. Computer programs provide the scripts for processing the rules. The exercise of reason, however, is more of an image processing function than a function composed of a series of rules. The exercise of reason is more right brain than left brain. It involves the interpretation of information and balancing inter-related alternatives. This paper will discuss a new way to define and process information that will give devices the ability to exercise human-like reasoning and judgment. The paper will discuss the characteristics of a "dynamic graphical language" in the context of addressing judgment, since judgment is often required to adjust rules when operating in a dynamic environment. The paper will touch on architecture issues and how judgment is integrated with rule processing.

  13. Electronic structure and magnetic properties of Pr-Co intermetallics: ab initio FP-LAPW calculations and correlation with experiments

    Science.gov (United States)

    Bakkari, Karim; Fersi, Riadh; Kebir Hlil, El; Bessais, Lotfi; Thabet Mliki, Najeh

    2018-03-01

    First-principle calculations combining density functional theory and the full-potential linearized augmented plane wave (FP-LAPW) method are performed to investigate the electronic and magnetic structure of Pr2Co7 in its two polymorphic forms, (2:7 H) and (2:7 R), for the first time. This type of calculation was also performed for PrCo5 and PrCo2 intermetallics. We have computed the valence density of states separately for spin-up and spin-down states in order to investigate the electronic band structure. This is governed by the strong contribution of the partial DOS of 3d-Co bands compared to the partial DOS of the 4f-Pr bands. Such a high ferromagnetic state is discussed in terms of the strong spin polarization observed in the total DOS. The magnetic moments carried by the Co and Pr atoms located in several sites for all compounds are computed. These results mainly indicate that cobalt atoms make a dominant contribution to the magnetic moments. The notable difference in the atomic moments of Pr and Co atoms between different structural slabs is explained in terms of the magnetic characteristics of the PrCo2 and PrCo5 compounds and the local chemical environments of the Pr and Co atoms in different structural slabs of Pr2Co7. From spin-polarized calculations we have simulated the 3d and 4f band population to estimate the local magnetic moments. These results are in accordance with the magnetic moments calculated using the FP-LAPW method. In addition, the exchange interactions J ij are calculated and used as input for M(T) simulations. Involving the data obtained from the electronic structure calculations, the appropriate Padé Table is applied to simulate the magnetization M(T) and to estimate the mean-field Curie temperature. We report a fairly good agreement between the ab initio calculation of magnetization and Curie temperature with the experimental data.

  14. First-principles calculation on dilute magnetic alloys in zinc blend crystal structure

    International Nuclear Information System (INIS)

    Ullah, Hamid; Inayat, Kalsoom; Khan, S.A; Mohammad, S.; Ali, A.; Alahmed, Z.A.; Reshak, A.H.

    2015-01-01

    Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic alloys in zinc blende structure. The first-principles study is carried out on Mn doped III–V semiconductors. The calculated band structures, electronic properties and magnetic properties of Ga 1−x Mn x X (X=P, As) compounds reveal that Ga 0.75 Mn 0.25 P is half metallic turned to be metallic with increasing x to 0.5 and 0.75, whereas substitute P by As cause to maintain the half-metallicity nature in both of Ga 0.75 Mn 0.25 As and Ga 0.5 Mn 0.5 As and tune Ga 0.25 Mn 0.75 As to be metallic. Calculated total magnetic moments and the robustness of half-metallicity of Ga 0.75 Mn 0.25 P, Ga 0.75 Mn 0.25 As and Ga 0.5 Mn 0.5 As with respect to the variation in lattice parameters are also discussed. The predicted theoretical evidence shows that some Mn-doped III–V semiconductors can be effectively used in spintronic devices

  15. First-principles calculation on dilute magnetic alloys in zinc blend crystal structure

    Energy Technology Data Exchange (ETDEWEB)

    Ullah, Hamid, E-mail: hamidullah@yahoo.com [Department of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat (Pakistan); Inayat, Kalsoom [Department of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat (Pakistan); Khan, S.A; Mohammad, S. [Department of Physics, Materials Modeling Laboratory, Hazara University, Mansehra 21300 (Pakistan); Ali, A. [Department of Advanced Materials Science & Engineering, Hanseo University, Seosan-si, Chungnam-do 356-706 (Korea, Republic of); Alahmed, Z.A. [Department of Physics and Astronomy, King Saud University, Riyadh 11451 (Saudi Arabia); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)

    2015-07-01

    Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic alloys in zinc blende structure. The first-principles study is carried out on Mn doped III–V semiconductors. The calculated band structures, electronic properties and magnetic properties of Ga{sub 1−x}Mn{sub x}X (X=P, As) compounds reveal that Ga{sub 0.75}Mn{sub 0.25}P is half metallic turned to be metallic with increasing x to 0.5 and 0.75, whereas substitute P by As cause to maintain the half-metallicity nature in both of Ga{sub 0.75}Mn{sub 0.25}As and Ga{sub 0.5}Mn{sub 0.5}As and tune Ga{sub 0.25}Mn{sub 0.75}As to be metallic. Calculated total magnetic moments and the robustness of half-metallicity of Ga{sub 0.75}Mn{sub 0.25}P, Ga{sub 0.75}Mn{sub 0.25}As and Ga{sub 0.5}Mn{sub 0.5}As with respect to the variation in lattice parameters are also discussed. The predicted theoretical evidence shows that some Mn-doped III–V semiconductors can be effectively used in spintronic devices.

  16. First-principles calculations of the magnetic anisotropy energy of Fe-V multilayers

    International Nuclear Information System (INIS)

    Le Bacq, O.; Eriksson, O.; Johansson, B.; James, P.; Delin, A.

    2002-06-01

    The magnetic anisotropy energy (MAE) of Fe 2 V-6, Fe 3 , and Fe 4 V 4 multilayers are investigated using first-principles spin-polarized and relativistic band-structure calculations based upon the full-potential linearized muffin-tin-orbital method. A strong difference in the MAE and the easy axis of magnetization (calculated for the experimental lattice parameters) is observed between the three studied multilayer systems, with easy axes of (001), (110), and (100) for Fe 2 V 6 , Fe 3 V 5 , and Fe-4V 4 , respectively. The MAE of the Fe 2 V6 and Fe 4 V 4 multilayers agrees well with the experimental data. The origin of this difference of behavior is analyzed, via a study of the influence of the atomic volume as well as a relaxation study of the multilayers with respect to the tetragonal deformation. The important role played by the c/a axial ratio, imposed by the alloying effects, is outlined. The magnetic anisotropy coefficients entering the expression of the MAE, as a function of the directional cosines, are extracted from a series of calculations for four independent spin directions. Finally, the band-filling effects on the MAE are analyzed as well as the different contributions in reciprocal space. (author)

  17. Maintaining clinical governance when giving telephone advice.

    Science.gov (United States)

    Alazawi, William; Agarwal, Kosh; Suddle, Abid; Aluvihare, Varuna; Heneghan, Michael A

    2013-10-01

    Delivering excellent healthcare depends on accurate communication between professionals who may be in different locations. Frequently, the first point of contact with the liver unit at King's College Hospital (KCH) is through a telephone call to a specialist registrar or liver fellow, for whom no case notes are available in which to record information. The aim of this study was to improve the clinical governance of telephone referrals and to generate contemporaneous records that could be easily retrieved and audited. An electronic database for telephone referrals and advice was designed and made securely available to registrars in our unit. Service development in a tertiary liver centre that receives referrals from across the UK and Europe. Demographic and clinical data were recorded prospectively and analysed retrospectively. Data from 350 calls were entered during 5 months. The information included the nature and origin of the call (200 from 75 different institutions), disease burden and severity of disease among the patients discussed with KCH, and outcome of the call. The majority of cases were discussed with consultants or arrangements were made for formal review at KCH. A telephone referrals and advice database provides clinical governance, serves as a quality indicator and forms a contemporaneous record at the referral centre. Activity data and knowledge of disease burden help to tailor services to the needs of referrers and commissioners. We recommend implementation of similar models in other centres that give extramural verbal advice.

  18. Cultivating gratitude and giving through experiential consumption.

    Science.gov (United States)

    Walker, Jesse; Kumar, Amit; Gilovich, Thomas

    2016-12-01

    Gratitude promotes well-being and prompts prosocial behavior. Here, we examine a novel way to cultivate this beneficial emotion. We demonstrate that 2 different types of consumption-material consumption (buying for the sake of having) and experiential consumption (buying for the sake of doing)-differentially foster gratitude and giving. In 6 studies we show that reflecting on experiential purchases (e.g., travel, meals out, tickets to events) inspires more gratitude than reflecting on material purchases (e.g., clothing, jewelry, furniture), and that thinking about experiences leads to more subsequent altruistic behavior than thinking about possessions. In Studies 1-2b, we use within-subject and between-subjects designs to test our main hypothesis: that people are more grateful for what they've done than what they have. Study 3 finds evidence for this effect in the real-world setting of online customer reviews: Consumers are more likely to spontaneously mention feeling grateful for experiences they have bought than for material goods they have bought. In our final 2 studies, we show that experiential consumption also makes people more likely to be generous to others. Participants who contemplated a significant experiential purchase behaved more generously toward anonymous others in an economic game than those who contemplated a significant material purchase. It thus appears that shifting spending toward experiential consumption can improve people's everyday lives as well as the lives of those around them. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

  19. Phonon spectra in the parent superconducting iron-tuned telluride F e1 +xTe from inelastic neutron scattering and ab initio calculations

    Science.gov (United States)

    Zbiri, Mohamed; Viennois, Romain

    2017-10-01

    We report inelastic neutron scattering measurements of phonon spectra in the parent superconductor iron-tuned chalcogenide F e1 +xTe for two different x contents (x ≤0.11 ) using neutron time-of-flight technique. Thermal neutron spectroscopy allowed the collection of the low-temperature Stokes spectra over an extended Q range at 2, 40, and 120 K, hence covering both the magnetic monoclinic and the paramagnetic tetragonal phases, whereas cold neutrons allowed the measurement of high-resolution anti-Stokes spectra at 140, 220, and 300 K, thus covering the tetragonal phase. Our results evidence a spin-phonon coupling behavior towards the observed noticeable temperature-dependent change of the Stokes spectra across the transition temperatures. On the other hand, the anti-Stokes spectra reveal a pronounced hardening of the low-energy, acoustic region of the phonon spectrum upon heating, indicating a strong anharmonicity and a subtle dependence of phonons on structural evolution within the tetragonal phase. Experimental results are accompanied by ab initio calculations of phonon spectra of the tetragonal stoichiometric phase for a comparison with the high-resolution anti-Stokes spectra. Calculations included different density functional methods. Spin polarization and van der Waals interaction were either considered or neglected, individually or concomitantly, in order to study their respective effect on lattice dynamics description. Our results suggest that including van der Waals interaction has only a slight effect on phonon dynamics; however, phonon spectra are better described when spin polarization is included in a cooperative way with van der Waals interactions.

  20. Calculated risks

    International Nuclear Information System (INIS)

    Rodricks, J.V.

    1992-01-01

    This book is a clear, practical, and balanced view of toxicology and risk management. The introduction argues the case for risks assessment and outlines the benefits and problems associated with chemical exposure. The first part of the book covers the basic science and the sources of human exposure to chemicals. Absorption, distribution, metabolism, and excretion are covered in some detail. The subsequent chapter gives a lively discussion of toxicity studies and then describes slow and fast poisons. The author gives the arguments for as well as against animal testing. There is much public bewilderment caused by reports of cancer-causing pesticides in apple juice and poisons emanating from nearby hazardous waste sites. The author believes that too much has been written in an attempt to expose governmental and corporate ignorance, negligence, and corruption. This book is less of a polemic, and more of a clear, unbiased clarification of the scientific basis for our concerns and uncertainties. It should serve to refocus the debate

  1. Multiconfiguration Dirac-Fock calculations of angle- and spin-resolved Auger spectra

    Energy Technology Data Exchange (ETDEWEB)

    Kleiman, U., E-mail: kleiman@mpipks-dresden.mpg.d [Max-Planck-Institut fuer Physik komplexer Systeme, Abteilung Endliche Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany); Lohmann, B. [Westfaelische Wilhelms-Universitaet Muenster, Institut fuer Theoretische Physik, Wilhelm-Klemm-Str. 9, D-48149 Muenster (Germany)

    2010-11-15

    The energies, line intensities as well as angular anisotropy and spin polarization parameters have been calculated for the L{sub 2,3}M{sub 1}M{sub 4,5} Auger spectra of Zn, Kr, Sr, Pd, Cd, Xe, Ba, Yb, Hg, Rn, Ra and No, the M{sub 2,3}N{sub 1}N{sub 4,5} Auger spectra of Pd, Cd, Xe, Ba, Yb, Hg, Rn, Ra and No, the N{sub 2,3}O{sub 1}O{sub 4,5} Auger spectra of Hg, Rn, Ra and No, the M{sub 4,5}N{sub 1}N{sub 2,3} Auger spectra of Kr, Sr, Pd, Cd, Xe, Ba, Yb, Hg, Rn, Ra and No, and the N{sub 4,5}O{sub 1}O{sub 2,3} Auger spectra of Xe, Ba, Yb, Hg, Rn, Ra and No. The calculations have been performed describing the Auger emission process in the context of scattering theory (relativistic distorted wave approximation) where the Auger transition amplitudes and scattering phases have been evaluated applying a relaxed orbital method within a multiconfiguration Dirac-Fock approach. Comparisons with other theoretical and experimental data are made wherever possible.

  2. Analysis gives the use he/she gives radioactive sources declared in disuse

    International Nuclear Information System (INIS)

    Velazquez Cruz, R.; Merayo Rodriguez, A.; Perez Gonzalez, F.

    1998-01-01

    Presently work is carried out an analysis the different factors that impact in the possibility for application the radioactive sources declared in disuse in the oriental territory entities in Cuba. With the objective to define the feasibility application sources declared in disuse, valuing the technical characteristics, the requirements give radiological protection, convenience use in other technological processes and the cost for those localized ones in the territory

  3. Rethinking the social and cultural dimensions of charitable giving

    DEFF Research Database (Denmark)

    Bajde, Domen

    2009-01-01

    Gifts to distant others, such as charitable giving, represent an important segment of contemporary gift-giving that has often been overlooked due to the excessive focus on dyadic giving between intimate individuals. In response, this paper adopts a sociological systemic perspective on gift......-giving and focuses on charitable gifts as an emblem of postmodern gift-giving to distant others. Historical evidence and sociological theory on postmodern solidarity are combined to shed light on the fluid duality of contemporary giving and the importance of the imaginary in charitable giving. The outlined socially...... symbolic dimensions of charitable giving are critically examined in light of postmodern consumer culture and the recent social corporate responsibility trends. By openly engaging the proposed complexities of gift-giving, our vocabulary and understanding of postmodern giving can be revised so as to invite...

  4. Reliability Calculations

    DEFF Research Database (Denmark)

    Petersen, Kurt Erling

    1986-01-01

    Risk and reliability analysis is increasingly being used in evaluations of plant safety and plant reliability. The analysis can be performed either during the design process or during the operation time, with the purpose to improve the safety or the reliability. Due to plant complexity and safety...... and availability requirements, sophisticated tools, which are flexible and efficient, are needed. Such tools have been developed in the last 20 years and they have to be continuously refined to meet the growing requirements. Two different areas of application were analysed. In structural reliability probabilistic...... approaches have been introduced in some cases for the calculation of the reliability of structures or components. A new computer program has been developed based upon numerical integration in several variables. In systems reliability Monte Carlo simulation programs are used especially in analysis of very...

  5. Evaluation gives the activity inventory the nuclear fuel irradiated and its radioactive waste

    International Nuclear Information System (INIS)

    Rodriguez Gual, Maritza

    1998-01-01

    The present work has as objectives to give a quantitative evaluation to the activity that possesses the nuclear fuel for 3,6% enrichment with a burnt one the 33 000 NWd/Tu proposed for the Juragua Nuclear Power Plant . In this work the method is used I calculate ORIGEN2. Obtained results are presented and they are compared with other calculations carried out in reactors type VVER-440

  6. First-principles calculation of the structure and electronic properties of Fe-substituted Bi2Ti2O7

    Science.gov (United States)

    Huang, Jin-Dou; Zhang, Zhenyi; Lin, Feng; Dong, Bin

    2017-12-01

    We performed first-principles calculations to investigate the formation energy, geometry structure, and electronic property of Fe-doped Bi2Ti2O7 systems with different Fe doping content. The calculated formation energies indicate that the substitutional configurations of Fe-doping Bi2Ti2O7 are easy to obtain under O-rich growth condition, but their thermodynamic stability decreases with the increase of Fe content. The calculated spin-resolved density of states and band structures indicate that the introduction of Fe into Bi2Ti2O7 brings high spin polarization. The spin-down impurity levels in Fe x Bi2-x Ti2O7 and spin-up impurity levels in Fe x Bi2Ti2-x O7 systems locate in the bottom of conduction band and narrow the band gap significantly, thus leading to the absorption of visible light. Interestingly, the impurity states in Fe x Bi2-x Ti2O7 are the efficient separation center of photogenerated electron and hole, and less affected by Fe doping content, in comparison, the levels of impurity band in Fe x Bi2Ti2-x O7 systems are largely effected by the Fe doping content, and high Fe doping content is the key factor to improve the separating rate of photogenerated electron and hole.

  7. Density Functional Theory Calculations of Activation Energies for Carrier Capture by Defects in Semiconductors

    Science.gov (United States)

    Modine, N. A.; Wright, A. F.; Lee, S. R.

    The rate of defect-induced carrier recombination is determined by both defect levels and carrier capture cross-sections. Density functional theory (DFT) has been widely and successfully used to predict defect levels, but only recently has work begun to focus on using DFT to determine carrier capture cross-sections. Lang and Henry developed the theory of carrier-capture by multiphonon emission in the 1970s and showed that carrier-capture cross-sections differ between defects primarily due to differences in their carrier capture activation energies. We present an approach to using DFT to calculate carrier capture activation energies that does not depend on an assumed configuration coordinate and that fully accounts for anharmonic effects, which can substantially modify carrier activation energies. We demonstrate our approach for intrinisic defects in GaAs and GaN and discuss how our results depend on the choice of exchange-correlation functional and the treatment of spin polarization. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  8. Ethics of trial drug use: to give or not to give?

    Science.gov (United States)

    Ebunoluwa, Oduwole O; Kareem, Fayemi A

    2016-01-01

    The 2014 outbreak of Ebola viral disease in some West African countries, which later spread to the USA and Spain, has continued to be a subject of global public health debate. While there is no approved vaccine or drug for Ebola cure yet, moral questions of bioethical significance are emerging even as vaccine studies are at different clinical trial phases. This paper, through a normative and critical approach, focuses on the question of whether it is ethical to give any experimental drugs to Ebola victims in West Africa or not. Given the global panic and deadly contagious nature of Ebola, this paper argues on three major compassionate grounds that it is ethical to use experimental drugs on the dying African victims of Ebola. Besides respecting patients and family consent in the intervention process, this paper argues that the use of Ebola trial drugs on West African population will be ethical if it promotes the common good, and does not violate the fundamental principles of transparency and integrity in human research ethics. Using Kantian ethical framework of universality as a basis for moral defense of allowing access to yet approved drugs. This paper provides argument to strengthen the compassionate ground provisional recommendation of the WHO's Strategic Advisory Group of Experts on Immunization (SAGE) on Ebola vaccines and vaccination.

  9. Who gives? Multilevel effects of gender and ethnicity on workplace charitable giving.

    Science.gov (United States)

    Leslie, Lisa M; Snyder, Mark; Glomb, Theresa M

    2013-01-01

    Research on diversity in organizations has largely focused on the implications of gender and ethnic differences for performance, to the exclusion of other outcomes. We propose that gender and ethnic differences also have implications for workplace charitable giving, an important aspect of corporate social responsibility. Drawing from social role theory, we hypothesize and find that gender has consistent effects across levels of analysis; women donate more money to workplace charity than do men, and the percentage of women in a work unit is positively related to workplace charity, at least among men. Alternatively and consistent with social exchange theory, we hypothesize and find that ethnicity has opposing effects across levels of analysis; ethnic minorities donate less money to workplace charity than do Whites, but the percentage of minorities in a work unit is positively related to workplace charity, particularly among minorities. The findings provide a novel perspective on the consequences of gender and ethnic diversity in organizations and highlight synergies between organizational efforts to increase diversity and to build a reputation for corporate social responsibility. PsycINFO Database Record (c) 2013 APA, all rights reserved.

  10. Alcohol Calorie Calculator

    Science.gov (United States)

    ... Alcohol Calorie Calculator Weekly Total 0 Calories Alcohol Calorie Calculator Find out the number of beer and ... Calories College Alcohol Policies Interactive Body Calculators Alcohol Calorie Calculator Alcohol Cost Calculator Alcohol BAC Calculator Alcohol ...

  11. Electronic structure and magnetic properties of quaternary Heusler alloys CoRhMnZ (Z = Al, Ga, Ge and Si) via first-principle calculations

    International Nuclear Information System (INIS)

    Benkabou, M.; Rached, H.; Abdellaoui, A.; Rached, D.; Khenata, R.

    2015-01-01

    First-principle calculations are performed to predict the electronic structure and elastic and magnetic properties of CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys. The calculations employ the full-potential linearized augmented plane wave. The exchange-correlations are treated within the generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE). The electronic structure calculations show that these compounds exhibit a gap in the minority states band and are clearly half-metallic ferromagnets, with the exception of the CoRhMnAl and CoRhMnGa, which are simple ferromagnets that are nearly half metallic in nature. The CoRhMnGe and CoRhMnSi compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule, which indicates the half metallicity and high spin polarization for these compounds. At the pressure transitions, these compounds undergo a structural phase transition from the Y-type I → Y-type II phase. We have determined the elastic constants C 11 , C 12 and C 44 and their pressure dependence, which have not previously been established experimentally or theoretically. - Highlights: • Based on DFT calculations, CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys were investigated. • The magnetic phase stability was determined from the total energy calculations. • The mechanical properties were investigated

  12. Electronic structure and magnetic properties of quaternary Heusler alloys CoRhMnZ (Z = Al, Ga, Ge and Si) via first-principle calculations

    Energy Technology Data Exchange (ETDEWEB)

    Benkabou, M. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, H. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Département de Physique, Faculté des Sciences, Université Hassiba Benbouali, Chlef 02000 (Algeria); Abdellaoui, A. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière, (LPQ3M), Université de Mascara, Mascara 29000 (Algeria); and others

    2015-10-25

    First-principle calculations are performed to predict the electronic structure and elastic and magnetic properties of CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys. The calculations employ the full-potential linearized augmented plane wave. The exchange-correlations are treated within the generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE). The electronic structure calculations show that these compounds exhibit a gap in the minority states band and are clearly half-metallic ferromagnets, with the exception of the CoRhMnAl and CoRhMnGa, which are simple ferromagnets that are nearly half metallic in nature. The CoRhMnGe and CoRhMnSi compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule, which indicates the half metallicity and high spin polarization for these compounds. At the pressure transitions, these compounds undergo a structural phase transition from the Y-type I → Y-type II phase. We have determined the elastic constants C{sub 11}, C{sub 12} and C{sub 44} and their pressure dependence, which have not previously been established experimentally or theoretically. - Highlights: • Based on DFT calculations, CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys were investigated. • The magnetic phase stability was determined from the total energy calculations. • The mechanical properties were investigated.

  13. Emerging economies a new force in international giving | IDRC ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    2014-03-04

    Mar 4, 2014 ... Emerging economies' increasing engagement in overseas philanthropy, private investment, and government aid is transforming the landscape of international giving, a groundbreaking study reports.

  14. First-principles calculations of a half-metallic ferromagnet zinc blende Zn{sub 1−x}V{sub x}Te

    Energy Technology Data Exchange (ETDEWEB)

    El Amine Monir, M.; Baltache, H. [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Murtaza, G. [Materials Modeling Laboratory, Department of Physics, Islamia College University, Peshawar (Pakistan); Azam, Sikander [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University Setif 1, 19000 Setif (Algeria); Al-Douri, Y. [Institute of Nano Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Ali, Roshan [Materials Modeling Lab, Department of Physics, Post Graduate Jahanzeb College, Swat (Pakistan)

    2015-03-15

    First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn{sub 1−x}V{sub x}Te for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn{sub 1−x}V{sub x}Te alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C{sub 11}, C{sub 12} and C{sub 44} are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn{sub 0.50}V{sub 0.50}Te and Zn{sub 0.75}V{sub 0.25}Te exhibit a half-metallic character, while Zn{sub 0.25}V{sub 0.75}Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δ{sub x}(d) and Δ{sub x}(pd) produced by the V(3d)-doped and s(p)–d exchange constants N{sub 0α} (conduction band) and N{sub 0β} (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µ{sub B} and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model. - Highlights: • Some physical properties of Vanadium doped ZnTe have been investigated. • Structural parameters for the parent compounds compare well with the available data. • The elastic and thermal properties are studied for the first time.

  15. 14 CFR 221.140 - Method of giving concurrence.

    Science.gov (United States)

    2010-01-01

    ...) Conflicting authority to be avoided. Care should be taken to avoid giving authority to two or more carriers... Aviation shall be used by a carrier to give authority to another carrier to issue and file with the... used as authority to file joint fares or charges in which the carrier to whom the concurrence is given...

  16. Modeling the probability of giving birth at health institutions among ...

    African Journals Online (AJOL)

    Background: Although ante natal care and institutional delivery is effective means for reducing maternal morbidity and mortality, the probability of giving birth at health institutions among ante natal care attendants has not been modeled in Ethiopia. Therefore, the objective of this study was to model predictors of giving birth at ...

  17. Ethics and Epistemology: Giving Back in the Klamath

    Directory of Open Access Journals (Sweden)

    Daniel Reid Sarna-Wojcicki

    2014-07-01

    Full Text Available This research note is part of the thematic section, Giving Back Through Collaboration in Practice, in the special issue titled “Giving Back in Field Research,” published as Volume 10, Issue 2 in the Journal of Research Practice.

  18. A Pilot Study of Nurses' Experience of Giving Spiritual Care

    Science.gov (United States)

    Deal, Belinda

    2010-01-01

    Using spiritual and religious resources gives patients and families strength to cope during a crisis, but nurses often do not offer spiritual care (Kloosterhouse & Ames, 2002). The purpose of this phenomenological study was to explore nurses" lived experience of giving spiritual care. A descriptive phenomenological approach was used to…

  19. Characterization of a multidrug resistant Salmonella enterica give ...

    African Journals Online (AJOL)

    Salmonella enterica Give is one of the serotypes that have been incriminated in Salmonella infections; sometimes associated with hospitalization and mortalities in humans and animals in some parts of the world. In this work, we characterized one Salmonella Give isolated from cloaca swab of an Agama agama lizard ...

  20. OPINION GIVING SERVICES AS A SOURCE OF CONSUMER INFORMATION

    Directory of Open Access Journals (Sweden)

    Joanna Wyrwisz

    2015-09-01

    Full Text Available The goal of the article is to determine the place and role of opinion giving services in consumer behaviours. The discussion is conducted around the thesis saying that in the information society, opinion giving services constitute an important source of information for consumers in the process of selecting and purchasing both products and services. In the article the research approach based on the theoretical and empirical examinations was presented. The discussion starts with presenting a defi nition and types of opinion giving services which constitute the base for the characteristics of activities and usefulness of web portals collecting consumers opinions. The use of opinion giving services provided in the purchase process was evaluated. An essential interest in other consumers opinions, placed in Internet, was observed together with perceiving them as credible. Positive assessment of the functionality of opinion giving services was noticed.

  1. The accompanying adult: authority to give consent in the UK.

    Science.gov (United States)

    Lal, Seema Madhur Lata; Parekh, Susan; Mason, Carol; Roberts, Graham

    2007-05-01

    Children may be accompanied by various people when attending for dental treatment. Before treatment is started, there is a legal requirement that the operator obtain informed consent for the proposed procedure. In the case of minors, the person authorized to give consent (parental responsibility) is usually a parent. To ascertain if accompanying persons of children attending the Department of Paediatric Dentistry at the Eastman Dental Hospital, London were empowered to give consent for the child's dental treatment. A total of 250 accompanying persons of children attending were selected, over a 6-month period. A questionnaire was used to establish whether the accompanying person(s) were authorized to give consent. The study showed that 12% of accompanying persons had no legal authority to give consent for the child's dental treatment. Clinicians need to be aware of the status of persons accompanying children to ensure valid consent is obtained.

  2. HENRY'S LAW CALCULATOR

    Science.gov (United States)

    On-Site was developed to provide modelers and model reviewers with prepackaged tools ("calculators") for performing site assessment calculations. The philosophy behind OnSite is that the convenience of the prepackaged calculators helps provide consistency for simple calculations,...

  3. Matrix isolation ESR spectroscopy and quantum chemical calculations on 5-methylhexa-1,2,4-triene-1,3-diyl, a highly delocalized triplet "hybrid" carbene.

    Science.gov (United States)

    Misochko, Eugenii Ya; Akimov, Alexander V; Korchagin, Denis V; Masitov, Artem A; Shavrin, Konstantin N

    2012-02-14

    The ESR spectrum of 5-methylhexa-1,2,4-triene-1,3-diyl (1) was recorded in an argon matrix at 15 K. The derived zero-field splitting (ZFS) parameters (D = 0.5054 ± 0.0006 cm(-1) and E = 0.0045 ± 0.0002 cm(-1)) fall between those determined previously for propargylene (2) and vinylcarbene (3). DFT and ab initio (CAS and MRCI) quantum-chemical calculations of the ZFS parameters of 1, 2, and 3 were performed. These calculations indicate that multireference methods are needed to successfully predict ZFS parameters of delocalized carbenes/biradicals such as 1-3. The calculated singly occupied MOs and spin density distributions show that the spin is more delocalized in 1 than in 2 and 3, indicating that 1 is a "hybrid" of the constituent ethynyl- and vinylcarbenes, 2 and 3, respectively. The dominant contribution to the D-value in 1 and 2 is found to result from spin-spin interactions on the C atoms of the propylidene moiety, which is strongly affected by spin polarization. Accurate values for the D-parameter are also predicted for other types of delocalized triplet carbenes such as HC(5)H and HCCN.

  4. Donor misreporting:conceptualizing social desirability bias in giving surveys

    OpenAIRE

    Lee, Zoe; Woodliffe, Lucy

    2010-01-01

    Although survey research is one of the most frequently used methods for studying charitable giving, the quality of the data is seldom stated or known. In particular, social desirability bias (SDB) has been found to distort data validity where respondents tend to over-report what is socially desirable and vice versa. We argue that this phenomenon has not been fully understood in the nonprofit context as existing social desirability scales are not appropriate to be used in giving surveys. Thus,...

  5. A general procedure to evaluate many-body spin operator amplitudes from periodic calculations: application to cuprates

    International Nuclear Information System (INIS)

    Moreira, Iberio de P R; Calzado, Carmen J; Malrieu, Jean-Paul; Illas, Francesc

    2007-01-01

    A general procedure is presented which permits the form of an extended spin Hamiltonian to be established for a given magnetic solid and the magnitude of its terms to be evaluated from spin polarized, Hartree-Fock or density functional calculations carried out for periodic models. The computational strategy makes use of a general mapping between the energy of pertinent broken-symmetry solutions and the diagonal terms of the spin Hamiltonian in a local representation. From this mapping it is possible to determine not only the amplitude of the well-known two-body magnetic coupling constants between near-neighbor sites, but also the amplitudes of four-body cyclic exchange terms. A scrutiny of the on-site spin densities provides additional information and control of the many broken-symmetry solutions which can be found. The procedure is applied to the La 2 CuO 4 , Sr 2 CuO 2 F 2 , Sr 2 CuO 2 Cl 2 and Ca 2 CuO 2 Cl 2 square lattices and the SrCu 2 O 3 ladder compound. It is shown that a proper description of the magnetic structure of these compounds requires that two- and four-body terms are explicitly included in the spin Hamiltonian. The implications for the interpretation of recent experiments are discussed

  6. Electronic, Magnetic, and Transport Properties of Polyacrylonitrile-Based Carbon Nanofibers of Various Widths: Density-Functional Theory Calculations

    Science.gov (United States)

    Partovi-Azar, P.; Panahian Jand, S.; Kaghazchi, P.

    2018-01-01

    Edge termination of graphene nanoribbons is a key factor in determination of their physical and chemical properties. Here, we focus on nitrogen-terminated zigzag graphene nanoribbons resembling polyacrylonitrile-based carbon nanofibers (CNFs) which are widely studied in energy research. In particular, we investigate magnetic, electronic, and transport properties of these CNFs as functions of their widths using density-functional theory calculations together with the nonequilibrium Green's function method. We report on metallic behavior of all the CNFs considered in this study and demonstrate that the narrow CNFs show finite magnetic moments. The spin-polarized electronic states in these fibers exhibit similar spin configurations on both edges and result in spin-dependent transport channels in the narrow CNFs. We show that the partially filled nitrogen dangling-bond bands are mainly responsible for the ferromagnetic spin ordering in the narrow samples. However, the magnetic moment becomes vanishingly small in the case of wide CNFs where the dangling-bond bands fall below the Fermi level and graphenelike transport properties arising from the π orbitals are recovered. The magnetic properties of the CNFs as well as their stability have also been discussed in the presence of water molecules and the hexagonal boron nitride substrate.

  7. Half metallic antiferromagnetic behavior in doped TiO2 rutile with double impurities (Os, Mo) from ab initio calculations

    International Nuclear Information System (INIS)

    Fakhim Lamrani, A.; Ouchri, M.; Belaiche, M.; El Kenz, A.

    2014-01-01

    Electronic and magnetic calculations were based on density functional theory within the generalized gradient approximation for II–VI compound semiconductor TiO 2 doped with single impurity Os and Mo; these compounds are half-metallic ferromagnets in their ground state with a total magnetic moment of 2μ B for both systems. Then, doping TiO 2 with double impurities (Os, Mo) was performed. As a result, Ti 1−2x Os x Mo x O 2 with x = 0.065 is a half-metallic antiferromagnet with 100% spin polarization of the conduction electrons crossing the Fermi level, without showing a net magnetization. Moreover, the Ti 14 OsMoO 32 compound is stable energetically than Ti 1−x Mo x O 2 and Ti 1−x Os x O 2 . The antiferromagnetic interaction in the Ti 1−2x Os x Mo x O 2 system is attributed to the double exchange mechanism, and the latter could also be the origin of their half-metallic behavior. - Highlights: • TiO 2 codoped with Os and Mo exhibits half-metallic diluted antiferromagnetic behavior. • TiO 2 doped with Mo exhibits half-metallic diluted ferromagnetic behavior. • TiO 2 doped with Os exhibits half-metallic diluted ferromagnetic behavior

  8. General-transformation matrix for Dirac spinors and the calculation of spinorial amplitudes

    International Nuclear Information System (INIS)

    Nam, K.; Moravcsik, M.J.

    1983-01-01

    A general transformation matrix T(p's';p,s) is constructed which transforms a Dirac spinor psi(p,s) into another Dirac spinor psi(p',s') with arbitrarily given momenta and polarization states by expoloting the so-called Stech operator as one of generators for those transformations. This transformation matrix is then used in a calculation to yield the spinorial matrix element M = anti psi(p',s')GAMMApsi(p,s) for any spin polarization state. The final expressions of these matrix elements show the explicit structure of spin dependence for the process described by these spinorial amplitudes. The kinematical limiting cases such as very low energy or high energy of the various matrix elements can also be easily displayed. Our method is superior to the existing one in the following points. Since we have a well-defined transformation operator between two Dirac spinor states, we can evaluate the necessary phase factor of the matrix elements in an unambiguous way without introducing the coordinate system. This enables us to write down the Feynman amplitudes of complicated processes in any spin basis very easily in terms of previously calculated matrix elements of anti psiGAMMApsi which are building blocks of those Feynman amplitudes. The usefulness of the results is illustrated on Compton scattering and on the elastic scattering of two identical massive leptons where the phase factor is important. It is also shown that the Stech operator as a polarization operator is simply related to the operator K = #betta#(polarized μ . polarized L + 1)/2 which is often used in bound state problems

  9. What drives the gender gap in charitable giving? Lower empathy leads men to give less to poverty relief.

    Science.gov (United States)

    Willer, Robb; Wimer, Christopher; Owens, Lindsay A

    2015-07-01

    We draw upon past research on gender and prosocial emotions in hypothesizing that empathy can help explain the gender gap in charitable giving. In a nationally representative survey, we found that men reported less willingness to give money or volunteer time to a poverty relief organization, gaps that were mediated by men's lower reported feelings of empathy toward others. We also experimentally tested how effective a variety of different ways of framing poverty relief were for promoting giving. Framing poverty as an issue that negatively affects all Americans increased men's willingness to donate to the cause, eliminating the gender gap. Mediation analysis revealed that this "aligned self-interest" framing worked by increasing men's reported poverty concern, not by changing their understanding of the causes of poverty. Thus, while men were generally less motivated by empathy, they responded to a framing that recast charitable giving as consistent with their self-interest. Exposure to the same framing, however, led women to report lower willingness to volunteer time for poverty relief, suggesting that framing giving as consistent with self-interest may discourage those who give because of an empathic response to poverty. Copyright © 2015 Elsevier Inc. All rights reserved.

  10. Collective philanthropy: describing and modeling the ecology of giving.

    Science.gov (United States)

    Gottesman, William L; Reagan, Andrew James; Dodds, Peter Sheridan

    2014-01-01

    Reflective of income and wealth distributions, philanthropic gifting appears to follow an approximate power-law size distribution as measured by the size of gifts received by individual institutions. We explore the ecology of gifting by analysing data sets of individual gifts for a diverse group of institutions dedicated to education, medicine, art, public support, and religion. We find that the detailed forms of gift-size distributions differ across but are relatively constant within charity categories. We construct a model for how a donor's income affects their giving preferences in different charity categories, offering a mechanistic explanation for variations in institutional gift-size distributions. We discuss how knowledge of gift-sized distributions may be used to assess an institution's gift-giving profile, to help set fundraising goals, and to design an institution-specific giving pyramid.

  11. Gift-giving in the medical student--patient relationship.

    Science.gov (United States)

    Alamri, Yassar Abdullah S

    2012-08-01

    There is paucity in the published literature that provides any ethical guidance guiding gift-giving within the student--patient relationship. This is perhaps because the dynamics of the medical student--patient relationship have not yet been explored as extensively as the doctor--patient relationship. More importantly, however, gift--giving in the doctor-patient relationship has traditionally been from the patient to the doctor and not vice versa. This article examines the literature published in this vicinity reflecting on an encounter with a patient.

  12. Authorization gives the personnel he/she gives the center he/she gives Isotopes for the acting he/she gives tied functions with the security and the radiological protection

    International Nuclear Information System (INIS)

    Perez Pijuan, S.; Hernandez Alvarez, R.; Peres Reyes, Y.; Venegas Bernal, M.C.

    1998-01-01

    The conception is described used in a center production labelled compound and radiopharmaceuticals for the authorization to the support, operation and supervision personnel The approaches are exposed used to define the excellent positions for the security the installation. The are described the training programs, designed starting from the indentification the specific competitions for each duty station and with particular emphasis in the development gives abilities you practice. It is used for the administration and evaluation gives the programs training the Automated System Administration Programs Training (GESAT)

  13. Nonlinear optical responses to circularly polarized lights of the surface state of a topological insulator

    Science.gov (United States)

    Misawa, Tetsuro; Yokoyama, Takehito; Murakami, Shuichi

    2012-02-01

    Recent photoelectron spectroscopy experiments have revealed the presence of the Dirac cone on the surface of the topological insulator and its spin-splitting due to the spin-orbit interaction. In general, on spin-orbit coupled systems, electric fields induce spin polarizations as linear and nonlinear responses. Here we investigate the inverse Faraday effect on the surface of the topological insulator. The inverse Faraday effect is a non-linear optical effect where a circularly polarized light induces a dc spin polarization. We employ the Keldysh Green's function method to calculate the induced spin polarization and discuss its frequency dependence. In particular, in the low frequency limit, our analytical result gives the spin polarization proportional to the frequency and the square of the lifetime. As for the finite frequency regime, we employ numerical methods to discuss the resonance due to interband transitions. We also discuss the photogalvanic effect, where an illumination of a circular polarized light generates the dc charge current. Lastly, we evaluate those quantities with realistic parameters.[4pt] [1] T. Misawa, T. Yokoyama, S. Murakami, Phys. Rev. B84, 165407 (2011).

  14. The conundrum of calculating carbon footprints

    DEFF Research Database (Denmark)

    Strobel, Bjarne W.; Erichsen, Anders Christian; Gausset, Quentin

    2016-01-01

    A pre-condition for reducing global warming is to minimise the emission of greenhouse gasses (GHGs). A common approach to informing people about the link between behaviour and climate change rests on developing GHG calculators that quantify the ‘carbon footprint’ of a product, a sector or an actor....... There is, however, an abundance of GHG calculators that rely on very different premises and give very different estimates of carbon footprints. In this chapter, we compare and analyse the main principles of calculating carbon footprints, and discuss how calculators can inform (or misinform) people who wish...

  15. Education Philanthropy Catching a Chill as Economy Cools Charitable Giving

    Science.gov (United States)

    Robelen, Erik W.

    2009-01-01

    This article reports that the recession tearing into the U.S. economy is not only straining the public coffers that support K-12 schooling, it's also taking a toll on education philanthropy. From family foundations to corporate philanthropies, charitable giving to K-12 education appears to be facing a downturn. Although no national figures are…

  16. Nursing and philanthropy: both about giving and joy.

    Science.gov (United States)

    Maloney, Joseph V

    2014-01-01

    There is a surprising intersection between nursing and charitable giving, and it is not about the money. Some nurses I know would find that statement to be a bit off-kilter. Maybe a few of them would find it even a bit off-putting. But there is, indeed, a strong case to be made that the two are of the same cloth.

  17. A Childhood Rich in Culture Gives a Socioeconomic Bonus

    DEFF Research Database (Denmark)

    Austring, Bennye Düranc

    2015-01-01

    Artiklen ridser den nyeste forskning op inden for feltet 'art rich learning', altså æstetiske læreprocesser af god kvalitet. In the book ”Art and Culture Give Children a Life that Works” 60 (Danish and non-Danish) experts, practitioners, artists and several Ministers from the Danish Government...

  18. Improving Evidence on Private Giving in Emerging Economies ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    Findings to improve private giving This three-year project will: -develop a critical mass of data on philanthropic and other private flows to developing countries from ... enabling environment for philanthropy exists; -promote research uptake and outreach by research teams in emerging economies and by the Centre for Global ...

  19. Improving Evidence on Private Giving in Emerging Economies ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    Despite growing philanthropy in emerging economies, there are significant data gaps on amounts and sources. There is also a lack of research on regulations and policies that support or discourage private giving. This research project will explore philanthropic cooperation in emerging and developing country contexts by ...

  20. A Conversation Model Enabling Intelligent Agents to Give Emotional Support

    NARCIS (Netherlands)

    Van der Zwaan, J.M.; Dignum, V.; Jonker, C.M.

    2012-01-01

    In everyday life, people frequently talk to others to help them deal with negative emotions. To some extent, everybody is capable of comforting other people, but so far conversational agents are unable to deal with this type of situation. To provide intelligent agents with the capability to give

  1. Why do firms give away their patents for free?

    NARCIS (Netherlands)

    Ziegler, Nicole; Gassmann, Oliver; Friesike, Sascha

    2013-01-01

    Within the trend of increasing patent commercialisation and open innovation, a recent phenomenon where firms give away their patents free of charge can be observed. This seems contradictory to the original intention of the patent system (enabling firms to create temporary monopolies to appropriate

  2. Nonverbal support giving induces nonverbal support seeking in depressed patients

    NARCIS (Netherlands)

    Geerts, E; Bouhuys, AL; Bloem, GM

    Nonverbal support seeking behavior of 11 mildly depressed patients was studied in relation to the nonverbal support giving behavior of a female interviewer. The patients were interviewed for 20 minutes during which the interviewer gave high and low nonverbal support for 10 minutes in a cross-over

  3. When may doctors give nurses telephonic treatment instructions?

    African Journals Online (AJOL)

    legal proxy cannot give consent, emergency treatment may be given without consent – provided it is not against a previous directive issued by a patient refusing treatment, e.g. a refusal to accept a blood transfusion for religious reasons.[8]. Before issuing telephonic instructions doctors should consider whether telephone ...

  4. Developing skills of giving and receiving feedbacks between ...

    African Journals Online (AJOL)

    One of the strategies to improve quality of teaching and learning at training institutes could be by developing the skill of giving and receiving feedbacks among the individuals involved in the training. This action research is then done as a final work for HDP in Jimma University (JU) to develop the skill of mutual ...

  5. Characterization of a Multidrug Resistant Salmonella Enterica Give

    African Journals Online (AJOL)

    Dr Olaleye

    levofloxacin resistant Salmonella Give that possessed gyrA mutation encoding histidine to Tyrosine conversion at amino acid 150(150His→Tyr) had been earlier isolated and characterized, one from septic poultry and one from asymptomatic pig (Ogunleye et al., 2011). The pig isolate possessed an additional (83Tyr→Ser) ...

  6. Motivation and the Power of Not Giving Up

    Science.gov (United States)

    ... site Sitio para adolescentes Body Mind Sexual Health Food & Fitness Diseases & Conditions Infections Drugs & Alcohol School & Jobs Sports Expert Answers (Q&A) Staying Safe Videos for Educators Search English Español Motivation and the Power of Not Giving Up KidsHealth / ...

  7. Informal care giving to more disabled people with multiple sclerosis.

    Science.gov (United States)

    Buchanan, Robert J; Radin, Dagmar; Chakravorty, Bonnie J; Tyry, Tuula

    2009-01-01

    About 30% of the people with multiple sclerosis (MS) require some form of home care assistance and 80% of that assistance is provided by informal or unpaid care givers. This study focusses on the care givers for 530 more disabled people with MS, with the objective of learning more about informal care giving to people with greater dependency and need for assistance. The data presented in this study were collected in a national survey of 530 people who provided informal care to more disabled people with MS. Almost half of these care givers reported that they provided more than 20 h of care per week to the person with MS, with more than 9 in 10 shopping for groceries, doing indoor housework, preparing meals or providing transportation for the person with MS. More than 4 in 10 employed care givers reduced the amount of time worked in the previous 12 months because of their care giving responsibilities. Although more than half of the MS care givers in our study reported that care giving was demanding, time consuming or challenging, about 90% of these MS care givers were happy that they could help. About two in three of these MS care givers found that care giving was rewarding, with more than 8 in 10 proud of the care they provided. More than a quarter of the informal care givers to people with MS thought they would benefit from treatment or counselling provided by mental health professionals. Not only it is necessary to provide access to mental health services for people with MS, but it is also important to assure that their informal care givers also have access to appropriate mental health care, given the scope of their care giving responsibilities.

  8. Magnetic Field Calculator

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Calculator will calculate the total magnetic field, including components (declination, inclination, horizontal intensity, northerly intensity,...

  9. Processes give selection location like fundamental approach gives the security for the repositories radioactive waste (radioactive installation) in Cuba

    International Nuclear Information System (INIS)

    Peralta Vidal, J.L.; Gil Castillo, R.O.; Chales Suarez, G.; Rodriguez Reyes, A.

    1998-01-01

    On the base for the best international practice, the requirements given by the IAEA, specialized national experience, the technician economic conditions and social matters give Cuba, it has been documented in the country the process the documented location for evacuation and storage the worn-out fuel lingeringly

  10. Ab initio calculations of martensitic phase behavior in Ni2FeGa magnetic shape memory alloys

    International Nuclear Information System (INIS)

    Soykan, C.; Özdemir Kart, S.; Sevik, C.; Çağın, T.

    2014-01-01

    Highlights: • L2 1 , NM and 5M phases have the energy minimum at a = 5.76 Å, c/a = 1.33 and c/a = 0.99. • Decrement in moment of Ni and increment in that of Fe reflect electrons transfer. • Differences in minority DOS over MT lead to stabilize the final structure. • C' taking small value in L2 1 leads to elastic instability in MT. - Abstract: A series of spin polarized energy calculations based on density functional theory (DFT) have been carried out to investigate the structural, magnetic, electronic and mechanical properties of Ni 2 FeGa magnetic shape memory alloys (MSMA’s) in the austenitic and martensitic structures. We report that L2 1 austenitic phase is metastable at a = 5.76 Å, the NM tetragonal and 5M monoclinic martensitic structures are stable at c/a = 1.33 and c/a = 0.99, respectively. That the electron removes from Ni to Fe site during phase transformation to martensite is confirmed by the increment in the magnetic moment of Ni, while decrement in that of Fe. The analysis of the partial density of states show that some distinguishable differences in the minority spin states occur upon martensitic phase transformation, such as, the replacement of the Fe states (e g and t 2g ) above Fermi level by only Fe-t 2g states during L2 1 -5M transformation and the splitting of Fe-t 2g states near Fermi level during 5M-NM transformation (through 7M). These changes lower the energy of the system, indicating that the final structure becomes stable. The soft tetragonal shear constant C′ of the austenitic phase designates the ease of the phase transition into martensitic phase. It is shown that the results calculated in this study are in good agreement with the previous calculations and the available experiments

  11. Framing charitable donations as exceptional expenses increases giving.

    Science.gov (United States)

    Sussman, Abigail B; Sharma, Eesha; Alter, Adam L

    2015-06-01

    Many articles have examined the psychological drivers of charitable giving, but little is known about how people mentally budget for charitable gifts. The present research aims to address this gap by investigating how perceptions of donations as exceptional (uncommon and infrequent) rather than ordinary (common and frequent) expenses might affect budgeting for and giving to charity. We provide the first demonstration that exceptional framing of an identical item can directly influence mental budgeting processes, and yield societal benefits. In 5 lab and field experiments, exceptional framing increased charitable behavior, and diminished the extent to which people considered the effect of the donation on their budgets. The current work extends our understanding of mental accounting and budgeting for charitable gifts, and demonstrates practical techniques that enable fundraisers to enhance the perceived exceptionality of donations. (c) 2015 APA, all rights reserved).

  12. Laser techniques for radioactive decontamination gives metallic surfaces

    International Nuclear Information System (INIS)

    Escobar Alracon, L.; Molina, G.; Vizuet Gonzalez, J.

    1998-01-01

    In this work it presented the prototype for system decontamination at diverse component with removable superficial contamination, using the technique gives laser ablation, for the evaporation at the pollutant. It discusses the principle in the fact that system, as well as the different elements that compose it. The are presented the obtained results when irradiating with a laser a surface without radioactive contamination to verify the system operation

  13. Giving away used injection equipment: missed prevention message?

    Directory of Open Access Journals (Sweden)

    Anstice Susan

    2010-02-01

    Full Text Available Abstract Background Our objective was to examine factors associated with distributive injection equipment sharing and how needle exchange programs (NEPs can help reduce distributive sharing among injection drug users (IDUs. Methods 145 English speaking Canadian IDUs ages 16 years and over who had injected in the past 30 days were recruited for a cross-sectional survey. Participants were asked about their socio-demographic characteristics, HIV risk behaviours, social support, drug treatment readiness, program satisfaction, health and social service use and NEP drug use. Bivariate statistics and logistic regression were used to characterize the population and examine correlates of sharing behaviour. Results More IDUs reported distributive sharing of cookers (45% than needles (36% or other types of equipment (water 36%; filters 29%; swabs 8%. Regression analyses revealed the following factors associated with distributing used cookers: a history of cocaine/crack injection, an Addiction Severity Index (ASI score indicative of a mental health problem, and older than 30 years of age. Factors associated with giving away used water included: male, injected methadone, injected other stimulants and moved 3+ times in the past 6 months. Factors associated with giving away used filters included: injected cocaine/crack or stayed overnight on the street or other public place. Factors associated with giving away swabs included: an ASI mental health score indicative of a mental health problem, and HCV negative status. Conclusions Our findings show that more IDUs give away cookers than needles or other injection equipment. While the results showed that correlates of sharing differed by piece of equipment, each point to distributive sharing by the most marginalized IDUs. Targeting prevention efforts to reduce equipment sharing in general, and cookers in particular is warranted to reduce use of contaminated equipment and viral transmission.

  14. Giving an account of one's pain in the anthropological interview.

    Science.gov (United States)

    Buchbinder, Mara

    2010-03-01

    In this paper, I analyze the illness stories narrated by a mother and her 13-year-old son as part of an ethnographic study of child chronic pain sufferers and their families. In examining some of the moral, relational and communicative challenges of giving an account of one's pain, I focus on what is left out of some accounts of illness and suffering and explore some possible reasons for these elisions. Drawing on recent work by Judith Butler (Giving an Account of Oneself, 2005), I investigate how the pragmatic context of interviews can introduce a form of symbolic violence to narrative accounts. Specifically, I use the term "genre of complaint" to highlight how anthropological research interviews in biomedical settings invoke certain typified forms of suffering that call for the rectification of perceived injustices. Interview narratives articulated in the genre of complaint privilege specific types of pain and suffering and cast others into the background. Giving an account of one's pain is thus a strategic and selective process, creating interruptions and silences as much as moments of clarity. Therefore, I argue that medical anthropologists ought to attend more closely to the institutional structures and relations that shape the production of illness narratives in interview encounters.

  15. Project W-320, 241-C-106 sluicing, master calculation list

    International Nuclear Information System (INIS)

    Bailey, J.W.

    1998-01-01

    This supporting document has been prepared to make the Master Calculation List readily retrievable. The list gives the status of the calculation (as-built, not used, applied, etc.), the calculation title, its originator, comments, and report number under which it was issued. Tank 241-C-106 has been included on the High Heat Load Watch List

  16. Bullet Design of MEMS Cantilever - Hand Calculation

    Directory of Open Access Journals (Sweden)

    Abhijeet V. KSHIRSAGAR

    2008-04-01

    Full Text Available The present article describes the basic hand calculations for design of MEMS cantilever for beginners. The MATLAB software code was written to analysis the all formulae. Further the article gives insight of important parameters, its dependence and consideration for a good design.

  17. Downhole telemetry system reliability calculation and improvement

    Science.gov (United States)

    Trofimova, E. S.; Rubtsova, O. O.; Ishchenko, A. V.; Danilov, V. Yu.

    2017-09-01

    The article gives an estimation and a calculation of the reliability indexes for the downhole telemetry system downhole unit under severe operating conditions of high temperature environment. The reliability-growth methods are suggested. It is shown that the use of redundancy significantly extends mean time to failure even in high temperature environment.

  18. Comparison of TRAC calculations with experimental data

    International Nuclear Information System (INIS)

    Jackson, J.F.; Vigil, J.C.

    1980-01-01

    TRAC is an advanced best-estimate computer code for analyzing postulated accidents in light water reactors. This paper gives a brief description of the code followed by comparisons of TRAC calculations with data from a variety of separate-effects, system-effects, and integral experiments. Based on these comparisons, the capabilities and limitations of the early versions of TRAC are evaluated

  19. GENMOD - A program for internal dosimetry calculations

    International Nuclear Information System (INIS)

    Dunford, D.W.; Johnson, J.R.

    1987-12-01

    The computer code GENMOD was created to calculate the retention and excretion, and the integrated retention for selected radionuclides under a variety of exposure conditions. Since the creation of GENMOD new models have been developed and interfaced to GENMOD. This report describes the models now included in GENMOD, the dosimetry factors database, and gives a brief description of the GENMOD program

  20. Using Angle calculations to demonstrate vowel shifts

    DEFF Research Database (Denmark)

    Fabricius, Anne

    2008-01-01

    This paper gives an overview of the long-term trends of diachronic changes evident within the short vowel system of RP during the 20th century. more specifically, it focusses on changing juxtapositions of the TRAP, STRUT and LOT, FOOT vowel centroid positions. The paper uses geometric calculation...

  1. impedance calculations of induction machine rotor conductors.

    African Journals Online (AJOL)

    Dr Obe

    ABSTRACT. The exact calculation of the impedance of induction machine rotor conductors at several operating frequencies are necessary if the dynamic behaviour of the machine is to give a good correlation between the simulated starting torque and current and the experimental results. This paper describes a method of'.

  2. Unified approach to alpha decay calculations

    Indian Academy of Sciences (India)

    2014-05-02

    May 2, 2014 ... In the light of these, the Wentzel–Kramers–. Brillouin (WKB) approximation .... effective Coulomb barrier at energy E gives transmission coefficient T and hence, can be used to calculate decay ... In solving the Schrödinger equation for the radial wave function Rl(r) it is convenient to use modified Schrödinger ...

  3. Electron and bremsstrahlung penetration and dose calculation

    Science.gov (United States)

    Watts, J. W., Jr.; Burrell, M. O.

    1972-01-01

    Various techniques for the calculation of electron and bremsstrahlung dose deposition are described. Energy deposition, transmission, and reflection coefficients for electrons incident on plane slabs are presented, and methods for their use in electron dose calculations were developed. A method using the straight-ahead approximation was also developed, and the various methods were compared and found to be in good agreement. Both accurate and approximate methods of calculating bremsstrahlung dose were derived and compared. Approximation is found to give a good estimate of dose where the electron spectrum falls off exponentially with energy.

  4. What are the impacts of giving up the driving licence?

    DEFF Research Database (Denmark)

    Siren, Anu Kristiina; Haustein, Sonja

    2014-01-01

    in their activities after giving up their licence. In travel frequency, neither the differences between renewers and non-renewers nor the changes over time within the groups were pronounced. The groups differed in their use of transport modes already at the baseline: the renewers drove, while nonrenewers travelled...... as passengers, used public transport, walked or cycled. Not renewing the licence was a strong predictor of unmet mobility needs, especially in relation to leisure activities. The present study indicates that younger seniors’ mobility is not likely to be affected by the strict renewal policies. However, given...

  5. Multiple acquisitions via sequential transfer of orphan spin polarization (MAeSTOSO): How far can we push residual spin polarization in solid-state NMR?

    Science.gov (United States)

    Gopinath, T; Veglia, Gianluigi

    2016-06-01

    Conventional multidimensional magic angle spinning (MAS) solid-state NMR (ssNMR) experiments detect the signal arising from the decay of a single coherence transfer pathway (FID), resulting in one spectrum per acquisition time. Recently, we introduced two new strategies, namely DUMAS (DUal acquisition Magic Angle Spinning) and MEIOSIS (Multiple ExperIments via Orphan SpIn operatorS), that enable the simultaneous acquisitions of multidimensional ssNMR experiments using multiple coherence transfer pathways. Here, we combined the main elements of DUMAS and MEIOSIS to harness both orphan spin operators and residual polarization and increase the number of simultaneous acquisitions. We show that it is possible to acquire up to eight two-dimensional experiments using four acquisition periods per each scan. This new suite of pulse sequences, called MAeSTOSO for Multiple Acquisitions via Sequential Transfer of Orphan Spin pOlarization, relies on residual polarization of both (13)C and (15)N pathways and combines low- and high-sensitivity experiments into a single pulse sequence using one receiver and commercial ssNMR probes. The acquisition of multiple experiments does not affect the sensitivity of the main experiment; rather it recovers the lost coherences that are discarded, resulting in a significant gain in experimental time. Both merits and limitations of this approach are discussed. Copyright © 2016 Elsevier Inc. All rights reserved.

  6. Noise in position measurement by centroid calculation

    International Nuclear Information System (INIS)

    Volkov, P.

    1996-01-01

    The position of a particle trajectory in a gaseous (or semiconductor) detector can be measured by calculating the centroid of the induced charge on the cathode plane. The charge amplifiers attached to each cathode strip introduce noise which is added to the signal. This noise broadens the position resolution line. Our article gives an analytical tool to estimate the resolution broadening due to the noise per strip and the number of strips involved in the centroid calculation. It is shown that the position resolution increases faster than the square root of the number of strips involved. We also consider the consequence of added interstrip capacitors, intended to diminish the differential nonlinearity. It is shown that the position error increases slower than linearly with the interstrip capacities, due to the cancellation of correlated noise. The estimation we give, can be applied to calculations of position broadening other than the centroid finding. (orig.)

  7. Effects of strain and quantum confinement in optically pumped nuclear magnetic resonance in GaAs: Interpretation guided by spin-dependent band structure calculations

    Science.gov (United States)

    Wood, R. M.; Saha, D.; McCarthy, L. A.; Tokarski, J. T.; Sanders, G. D.; Kuhns, P. L.; McGill, S. A.; Reyes, A. P.; Reno, J. L.; Stanton, C. J.; Bowers, C. R.

    2014-10-01

    A combined experimental-theoretical study of optically pumped nuclear magnetic resonance (OPNMR) has been performed in a GaAs /A l0.1G a0.9As quantum well film epoxy bonded to a Si substrate with thermally induced biaxial strain. The photon energy dependence of the Ga OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from the electronic structure and differential absorption to spin-up and spin-down states of the electron conduction band using a modified k .p model based on the Pidgeon-Brown model. Comparison of theory with experiment facilitated the assignment of features in the OPNMR energy dependence to specific interband Landau level transitions. The results provide insight into how effects of strain and quantum confinement are manifested in optical nuclear polarization in semiconductors.

  8. The influence of relationship beliefs on gift giving

    Directory of Open Access Journals (Sweden)

    Rai Dipankar

    2017-12-01

    Full Text Available People have fundamental beliefs about what constitutes a good relationship, known as implicit theories of relationship, where some people have destiny beliefs whereas others have growth beliefs. People with destiny beliefs believe that potential partners are meant either for each other or not, whereas people with growth beliefs believe that successful relationships are cultivated and developed. This research shows that different implicit theories of relationship influence consumers’ gift choice to their significant others. We demonstrate, through two studies, that consumers with destiny beliefs prefer giving gifts that are more feasible in nature, whereas consumers with growth beliefs prefer giving gifts that are more desirable in nature. We show that this effect is mediated by desirability-feasibility considerations. Specifically, consumers with destiny beliefs focus on feasibility considerations, which leads them to choose a highly feasible gift. Conversely, consumers with growth beliefs focus on desirability considerations, which leads them to choose a highly desirable gift. We also discuss the theoretical and managerial implications of our research.

  9. Reasons women give for abortion: a review of the literature.

    Science.gov (United States)

    Kirkman, Maggie; Rowe, Heather; Hardiman, Annarella; Mallett, Shelley; Rosenthal, Doreen

    2009-12-01

    The aim was to identify from empirical research that used quantitative or qualitative methods the reasons women give for having an abortion. A search was conducted of peer-reviewed, English language publications indexed in eight computerized databases with publication date 1996-2008, using keywords 'abortion' and 'reason' (Medline: 'induced abortion' OR 'termination of pregnancy' OR 'elective abortion' and 'reason'). Inclusion criteria were empirical research on humans that identified women's reasons for undergoing an abortion, conducted in 'high-income' countries. 19 eligible papers were found. Despite variation in methods of generating, collecting, and analysing reasons, and the inadequacy of methodological detail in some papers, all contributed to a consistent picture of the reasons women give for having an abortion, with three main categories ('Woman-focused', 'Other-focused', and 'Material') identified. Ambivalence was often evident in women's awareness of reasons for continuing the pregnancy, but abortion was chosen because continuing with the pregnancy was assessed as having adverse effects on the life of the woman and significant others. Women's reasons were complex and contingent, taking into account their own needs, a sense of responsibility to existing children and the potential child, and the contribution of significant others, including the genetic father.

  10. Who Is Giving Feedback To Whom In Entrepreneurship Education?

    DEFF Research Database (Denmark)

    Trolle Elmholdt, Stine; Warhuus, Jan; Blenker, Per

    evaluate and provide feedback on, with regard to both the teaching and the learning that takes place in these types of courses. We therefore ask: Who is giving feedback to whom in entrepreneurship education - and for what purpose?The intent of the paper is to develop and explore the system of feedback......The question we care about (objectives):When entrepreneurship is taught through the process of practicing entrepreneurship and based on experiential learning, a need arises for different forms of assessment, evaluation, and feedback procedures than those applied to traditional forms of higher...... is at play that involves both feedback among educators and students and between educators and students;3. that the complexity is further increased when it is acknowledged that the subject of the feedback may concern the learning, the teaching, the process, the object of the process (the entrepreneurial...

  11. Giving the influenza jab: a review of the law.

    Science.gov (United States)

    Griffiths, Richard

    2004-10-01

    District nursing sister June Harris recently completed the administration of 30 'flu jabs to frail older residents of a local care home. June encountered a number of problems when administering the vaccinations. Relatives of five residents with advanced dementia did not want them to have the injection, mainly because they had heard that it would give the recipient the 'flu. An 85-year-old resident has complained that while she agreed to have a 'flu jab it now appears she also had a pneumococcal vaccination as well that no one told her about. More seriously, June has recently heard that one resident is in hospital having contracted Guillian-Barre Syndrome as a result of the vaccination. June remembers that this reluctant resident specifically asked if the 'flu jab would leave her paralysed and June had laughingly replied that she had not paralysed anyone to date. The residents and their families are now threatening legal action.

  12. The Effect of Giving Feedback to Students' Writing

    Directory of Open Access Journals (Sweden)

    Mochamad Zainuddin

    2004-01-01

    Full Text Available Although writing is as important as other skills such as listening, speaking, and reading, it needs more special attention. In order to write well, students need a long process to learn to write and they need continous feedback. The aim of this article is to know whether giving feedback to students' writing has a significant effect or not. Two groups of students, experimental and control, were involved. The compositions of the first group were given feedback, while those of the second group were not given feedback. The study shows that provision of feedback improves student's writing. In light of the result of the study, it is recommended that teachers provide feedback on students' writing.

  13. Paedomorphic facial expressions give dogs a selective advantage.

    Directory of Open Access Journals (Sweden)

    Bridget M Waller

    Full Text Available How wolves were first domesticated is unknown. One hypothesis suggests that wolves underwent a process of self-domestication by tolerating human presence and taking advantage of scavenging possibilities. The puppy-like physical and behavioural traits seen in dogs are thought to have evolved later, as a byproduct of selection against aggression. Using speed of selection from rehoming shelters as a proxy for artificial selection, we tested whether paedomorphic features give dogs a selective advantage in their current environment. Dogs who exhibited facial expressions that enhance their neonatal appearance were preferentially selected by humans. Thus, early domestication of wolves may have occurred not only as wolf populations became tamer, but also as they exploited human preferences for paedomorphic characteristics. These findings, therefore, add to our understanding of early dog domestication as a complex co-evolutionary process.

  14. Duchenne muscular dystrophy: genome editing gives new hope for treatment.

    Science.gov (United States)

    Crispi, Vassili; Matsakas, Antonios

    2018-01-31

    Duchenne muscular dystrophy (DMD) is a progressive wasting disease of skeletal and cardiac muscles, representing one of the most common recessive fatal inherited genetic diseases with 1:3500-1:5000 in yearly incidence. It is caused by mutations in the DMD gene that encodes the membrane-associated dystrophin protein. Over the years, many have been the approaches to management of DMD, but despite all efforts, no effective treatment has yet been discovered. Hope for the development of potential therapeutics has followed the recent advances in genome editing and gene therapy. This review gives an overview to DMD and summarises current lines of evidence with regard to treatment and disease management alongside the appropriate considerations. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

  15. Conditions needed to give meaning to rad-equivalence principle

    International Nuclear Information System (INIS)

    Latarjet, R.

    1980-01-01

    To legislate on mutagenic chemical pollution the problem to be faced is similar to that tackled about 30 years ago regarding pollution by ionizing radiations. It would be useful to benefit from the work of these 30 years by establishing equivalences, if possible, between chemical mutagens and radiations. Inevitable mutagenic pollutions are considered here, especially those associated with fuel based energy production. As with radiations the legislation must derive from a compromise between the harmful and beneficial effects of the polluting system. When deciding on tolerance doses it is necessary to safeguard the biosphere without inflicting excessive restrictions on industry and on the economy. The present article discusses the conditions needed to give meaning to the notion of rad-equivalence. Some examples of already established equivalences are given, together with the first practical consequences which emerge [fr

  16. What are the impacts of giving up the driver license?

    DEFF Research Database (Denmark)

    Siren, Anu Kristiina; Haustein, Sonja

    -being, and modal choices and transportation patterns. Results: Non-renewers had poorer health already at baseline. However, they did become more dependent on others in their out-of-home activities after giving up their license. In travel frequency, neither the differences between renewers and non-renewers nor...... the changes over time within the groups were pronounced. Non-renewers reported more unmet mobility needs both in 2009 and 2012, especially in relation to leisure activities. The groups differed significantly in their use of transport modes. The renewers drove more often as the main transport mode, while non......-renewers traveled in the car as passengers, used public transport, walked or cycled. Discussion: The present study indicates that younger seniors’ mobility is probably not affected by the renewal policies. However, given the positive economic and safety consequences of independent mobility in old age, society...

  17. Uranium oxide recycling to give more sustainable power generation

    International Nuclear Information System (INIS)

    Hagger, R.; Garner, D.S.J.; Beaumont, D.M.; Hesketh, K.

    2001-01-01

    In broad terms there are two routes for irradiated nuclear fuel, the closed cycle involving recycling and the open cycle culminating in direct disposal. The benefits of following the closed cycle are presented. The environmental burdens associated with open and closed cycles are compared using Life Cycle Assessment (LCA) for non-active burdens and human irradiation. Consideration is given to the extension of the nuclear fuel cycle to include a proportion of MOX fuel elements within a reactor core, and the impact in terms of total activity, waste volumes and Integrated Toxic Potential (ITP) discussed. The potential of moving to a fast reactor cycle is also raised in support of the recycling of spent nuclear fuel giving sustainable power generation. (author)

  18. IMPACT OF THE “GIVING CIGARETTES IS GIVING HARM” CAMPAIGN ON KNOWLEDGE AND ATTITUDES OF CHINESE SMOKERS

    Science.gov (United States)

    Huang, Li-Ling; Thrasher, James F.; Jiang, Yuan; Li, Qiang; Fong, Geoffrey T.; Chang, Yvette; Walsemann, Katrina M.; Friedman, Daniela B.

    2015-01-01

    Objective To date there is limited published evidence on the efficacy of tobacco control mass media campaigns in China. This study aimed to evaluate the impact of a mass media campaign “Giving Cigarettes is Giving Harm” (GCGH) on Chinese smokers’ knowledge of smoking-related harms and attitudes toward cigarette gifts. Methods Population-based, representative data were analyzed from a longitudinal cohort of 3,709 adult smokers who participated in the International Tobacco Control China Survey conducted in six Chinese cities before and after the campaign. Logistic regression models were estimated to examine associations between campaign exposure and attitudes about cigarettes as gifts measured post-campaign. Poisson regression models were estimated to assess the effects of campaign exposure on post-campaign knowledge, adjusting for pre-campaign knowledge. Findings Fourteen percent (n=335) of participants recalled the campaign within the cities where the GCGH campaign was implemented. Participants in the intervention cities who recalled the campaign were more likely to disagree that cigarettes are good gifts (71% vs. 58%, pcampaign-targeted knowledge than those who did not recall the campaign (Mean=1.97 vs. 1.62, pcampaign-targeted knowledge were similar in both cities, perhaps due to a secular trend, low campaign recall, or contamination issues. Conclusions These findings suggest that the GCGH campaign increased knowledge of smoking harms, which could promote downstream cessation. Findings provide evidence to support future campaign development to effectively fight the tobacco epidemic in China. PMID:24813427

  19. The difference between "giving a rose" and "giving a kiss": Sustained neural activity to the light verb construction.

    Science.gov (United States)

    Wittenberg, Eva; Paczynski, Martin; Wiese, Heike; Jackendoff, Ray; Kuperberg, Gina

    2014-05-01

    We used event-related potentials (ERPs) to investigate the neurocognitive mechanisms associated with processing light verb constructions such as "give a kiss". These constructions consist of a semantically underspecified light verb ("give") and an event nominal that contributes most of the meaning and also activates an argument structure of its own ("kiss"). This creates a mismatch between the syntactic constituents and the semantic roles of a sentence. Native speakers read German verb-final sentences that contained light verb constructions (e.g., "Julius gave Anne a kiss"), non-light constructions (e.g., "Julius gave Anne a rose"), and semantically anomalous constructions (e.g., *"Julius gave Anne a conversation"). ERPs were measured at the critical verb, which appeared after all its arguments. Compared to non-light constructions, the light verb constructions evoked a widely distributed, frontally focused, sustained negative-going effect between 500 and 900 ms after verb onset. We interpret this effect as reflecting working memory costs associated with complex semantic processes that establish a shared argument structure in the light verb constructions.

  20. Core calculations of JMTR

    Energy Technology Data Exchange (ETDEWEB)

    Nagao, Yoshiharu [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment

    1998-03-01

    In material testing reactors like the JMTR (Japan Material Testing Reactor) of 50 MW in Japan Atomic Energy Research Institute, the neutron flux and neutron energy spectra of irradiated samples show complex distributions. It is necessary to assess the neutron flux and neutron energy spectra of an irradiation field by carrying out the nuclear calculation of the core for every operation cycle. In order to advance core calculation, in the JMTR, the application of MCNP to the assessment of core reactivity and neutron flux and spectra has been investigated. In this study, in order to reduce the time for calculation and variance, the comparison of the results of the calculations by the use of K code and fixed source and the use of Weight Window were investigated. As to the calculation method, the modeling of the total JMTR core, the conditions for calculation and the adopted variance reduction technique are explained. The results of calculation are shown. Significant difference was not observed in the results of neutron flux calculations according to the difference of the modeling of fuel region in the calculations by K code and fixed source. The method of assessing the results of neutron flux calculation is described. (K.I.)

  1. Electrical installation calculations basic

    CERN Document Server

    Kitcher, Christopher

    2013-01-01

    All the essential calculations required for basic electrical installation workThe Electrical Installation Calculations series has proved an invaluable reference for over forty years, for both apprentices and professional electrical installation engineers alike. The book provides a step-by-step guide to the successful application of electrical installation calculations required in day-to-day electrical engineering practice. A step-by-step guide to everyday calculations used on the job An essential aid to the City & Guilds certificates at Levels 2 and 3Fo

  2. Electrical installation calculations advanced

    CERN Document Server

    Kitcher, Christopher

    2013-01-01

    All the essential calculations required for advanced electrical installation workThe Electrical Installation Calculations series has proved an invaluable reference for over forty years, for both apprentices and professional electrical installation engineers alike. The book provides a step-by-step guide to the successful application of electrical installation calculations required in day-to-day electrical engineering practiceA step-by-step guide to everyday calculations used on the job An essential aid to the City & Guilds certificates at Levels 2 and 3For apprentices and electrical installatio

  3. Evapotranspiration Calculator Desktop Tool

    Science.gov (United States)

    The Evapotranspiration Calculator estimates evapotranspiration time series data for hydrological and water quality models for the Hydrologic Simulation Program - Fortran (HSPF) and the Stormwater Management Model (SWMM).

  4. Waste Package Lifting Calculation

    International Nuclear Information System (INIS)

    H. Marr

    2000-01-01

    The objective of this calculation is to evaluate the structural response of the waste package during the horizontal and vertical lifting operations in order to support the waste package lifting feature design. The scope of this calculation includes the evaluation of the 21 PWR UCF (pressurized water reactor uncanistered fuel) waste package, naval waste package, 5 DHLW/DOE SNF (defense high-level waste/Department of Energy spent nuclear fuel)--short waste package, and 44 BWR (boiling water reactor) UCF waste package. Procedure AP-3.12Q, Revision 0, ICN 0, calculations, is used to develop and document this calculation

  5. Radar Signature Calculation Facility

    Data.gov (United States)

    Federal Laboratory Consortium — FUNCTION: The calculation, analysis, and visualization of the spatially extended radar signatures of complex objects such as ships in a sea multipath environment and...

  6. Electronics Environmental Benefits Calculator

    Data.gov (United States)

    U.S. Environmental Protection Agency — The Electronics Environmental Benefits Calculator (EEBC) was developed to assist organizations in estimating the environmental benefits of greening their purchase,...

  7. Does friendship give us non-derivative partial reasons ?

    Directory of Open Access Journals (Sweden)

    Andrew Reisner

    2008-02-01

    Full Text Available One way to approach the question of whether there are non-derivative partial reasons of any kind is to give an account of what partial reasons are, and then to consider whether there are such reasons. If there are, then it is at least possible that there are partial reasons of friendship. It is this approach that will be taken here, and it produces several interesting results. The first is a point about the structure of partial reasons. It is at least a necessary condition of a reason’s being partial that it has an explicit relational component. This component, technically, is a relatum in the reason relation that itself is a relation between the person to whom the reason applies and the person whom the action for which there is a reason concerns. The second conclusion of the paper is that this relational component is also required for a number of types of putatively impartial reasons. In order to avoid trivialising the distinction between partial and impartial reasons, some further sufficient condition must be applied. Finally, there is some prospect for a way of distinguishing between impartial reasons that contain a relational component and partial reasons, but that this approach suggests that the question of whether ethics is partial or impartial will be settled at the level of normative ethical discourse, or at least not at the level of discourse about the nature of reasons for action.

  8. Graphene-based spintronic components

    OpenAIRE

    Zeng, Minggang; Shen, Lei; Su, Haibin; Zhou, Miao; Zhang, Chun; Feng, Yuanping

    2010-01-01

    A major challenge of spintronics is in generating, controlling and detecting spin-polarized current. Manipulation of spin-polarized current, in particular, is difficult. We demonstrate here, based on calculated transport properties of graphene nanoribbons, that nearly +-100% spin-polarized current can be generated in zigzag graphene nanoribbons (ZGNRs) and tuned by a source-drain voltage in the bipolar spin diode, in addition to magnetic configurations of the electrodes. This unusual transpor...

  9. [Understanding dosage calculations].

    Science.gov (United States)

    Benlahouès, Daniel

    2016-01-01

    The calculation of dosages in paediatrics is the concern of the whole medical and paramedical team. This activity must generate a minimum of risks in order to prevent care-related adverse events. In this context, the calculation of dosages is a practice which must be understood by everyone. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

  10. PWR core design calculations

    International Nuclear Information System (INIS)

    Trkov, A.; Ravnik, M.; Zeleznik, N.

    1992-01-01

    Functional description of the programme package Cord-2 for PWR core design calculations is presented. Programme package is briefly described. Use of the package and calculational procedures for typical core design problems are treated. Comparison of main results with experimental values is presented as part of the verification process. (author) [sl

  11. Calculativeness and trust

    DEFF Research Database (Denmark)

    Frederiksen, Morten

    2014-01-01

    Williamson’s characterisation of calculativeness as inimical to trust contradicts most sociological trust research. However, a similar argument is found within trust phenomenology. This paper re-investigates Williamson’s argument from the perspective of Løgstrup’s phenomenological theory of trust....... Contrary to Williamson, however, Løgstrup’s contention is that trust, not calculativeness, is the default attitude and only when suspicion is awoken does trust falter. The paper argues that while Williamson’s distinction between calculativeness and trust is supported by phenomenology, the analysis needs...... into consideration that people often engage in interaction on the basis of familiarity rather than calculation. Finally, the institutionally multi-layered character of social interaction means that trust and calculativeness cannot a priori be separated into non-market and market relations. Rather, it is reasonable...

  12. Reactor physics calculations in the Nordic countries

    International Nuclear Information System (INIS)

    Hoeglund, R.

    1995-01-01

    The seventh biennial meeting on reactor physics calculations in the Nordic countries was arranged by VTT Energy on May 8-9, 1995. 26 papers on different subjects in the field of reactor physics were presented by 45 participants representing research establishments, technical universities, utilities, consultants and suppliers. Resent development and verification of the program systems of ABB Atom, Risoe, Scandpower, Studsvik and VTT Energy were the main topic of the meeting. Benchmarking of the two assembly codes CASMO-4 and HELIOS is proceeding. Cross section data calculated with CASMO-HEX have been validated for the Loviisa reactors. On core analysis ABB atom gives a description on its latest core simulator version POLCA7 with the calculation Core Master 2 and the BWR core supervision system Core Watch. Transient calculations with HEXTRAN, HEXTRAN- PLIM, TRAB, RAMONA, SIMULATE-3K and a code based on PRESTO II/POLCA7 were also presented

  13. Dose rate calculations for a reconnaissance vehicle

    International Nuclear Information System (INIS)

    Grindrod, L.; Mackey, J.; Salmon, M.; Smith, C.; Wall, S.

    2005-01-01

    A Chemical Nuclear Reconnaissance System (CNRS) has been developed by the British Ministry of Defence to make chemical and radiation measurements on contaminated terrain using appropriate sensors and recording equipment installed in a land rover. A research programme is under way to develop and validate a predictive capability to calculate the build-up of contamination on the vehicle, radiation detector performance and dose rates to the occupants of the vehicle. This paper describes the geometric model of the vehicle and the methodology used for calculations of detector response. Calculated dose rates obtained using the MCBEND Monte Carlo radiation transport computer code in adjoint mode are presented. These address the transient response of the detectors as the vehicle passes through a contaminated area. Calculated dose rates were found to agree with the measured data to be within the experimental uncertainties, thus giving confidence in the shielding model of the vehicle and its application to other scenarios. (authors)

  14. Simulated parents: developing paediatric trainees' skills in giving bad news.

    Science.gov (United States)

    Gough, Jenny K; Frydenberg, Alexis R; Donath, Susan K; Marks, Michael M

    2009-03-01

    In curriculum documents for medicine in undergraduate, post-graduate and continuing professional development, there is now a focus on communication skills. The challenges are to place communication skills in the crowded curriculum and then to construct and sustain a programme that uses an evidence-based approach to the teaching and learning of communication skills. For 6 years, we have conducted a programme that involves simulated parents supporting junior medical staff to refine their skills in communication, particularly in giving parents bad news. The aim of our study was to obtain a better understanding of the trainees' experiences of the programme. Nine junior residents individually worked through two scenarios and received feedback from the simulated parent. They gave bad news to a simulated parent/actor who then gave feedback. A recording of the simulation was provided for discussion with a designated colleague at an arranged time. The tapes were then separately appraised by two independent raters - another actor and a paediatrician. Brief written reports and conducted semi-structured interviews provided more insights into the trainees' experience of the simulation. Other participating medical/medical education staff were interviewed about the simulation programme. Five themes emerged from the qualitative data: timeliness, emotional safety, the complexity of communication, practical usefulness and the challenge of effecting change. In addition, the ratings of the videos helped to clarify those 'parent-centred' communication skills that trainees may neglect in difficult conversations: 'ask about support', 'encourage the parent to ask questions' and 'repeat key messages'. The evaluation highlighted the value of an early-career experiential programme to highlight the importance of communication skills in post-graduate paediatrics practice.

  15. Giving birth with rape in one's past: a qualitative study.

    Science.gov (United States)

    Halvorsen, Lotta; Nerum, Hilde; Oian, Pål; Sørlie, Tore

    2013-09-01

    Rape is one of the most traumatizing violations a woman can be subjected to, and leads to extensive health problems, predominantly psychological ones. A large proportion of women develop a form of posttraumatic stress termed Rape Trauma Syndrome. A previous study by our research group has shown that women with a history of rape far more often had an operative delivery in their first birth and those who gave birth vaginally had second stages twice as long as women with no history of sexual assault. The aim of this study is to examine and illuminate how women previously subjected to rape experience giving birth for the first time and their advice on the kind of birth care they regard as good for women with a history of rape. A semi-structured interview with 10 women, who had been exposed to rape before their first childbirth. Data on the birth experience were analyzed by qualitative content analysis. The main theme was "being back in the rape" with two categories: "reactivation of the rape during labor," with subcategories "struggle," "surrender," and "escape" and "re-traumatization after birth," with the subcategories "objectified," "dirtied," and "alienated body." A rape trauma can be reactivated during the first childbirth regardless of mode of delivery. After birth, the women found themselves re-traumatized with the feeling of being dirtied, alienated, and reduced to just a body that another body is to come out of. Birth attendants should acknowledge that the common measures and procedures used during normal birth or cesarean section can contribute to a reactivation of the rape trauma. © 2013, Copyright the Authors Journal compilation © 2013, Wiley Periodicals, Inc.

  16. Saving reed lands by giving economic value to reed

    Directory of Open Access Journals (Sweden)

    F.W. Croon

    2014-07-01

    Full Text Available Discussions about the need for renewable energy, the need for nature conservation, the need to double the world’s food production to eliminate hunger, the need to reduce carbon dioxide emission, and the wish to reduce dependency on dwindling oil resources, show that these issues are intimately related and sometimes mutually exclusive. The use of food crops for the production of renewable fuels has resulted in the energy vs. food debate; the use of scarce land and fresh water for the dedicated production of biomass conflicts with food production and nature conservation; the collection of harvest residues and forest wastes as biomass to produce renewable fuels is complex and leaves a CO2 footprint. The several species of reed that grow naturally in deltas, river plains etc. can provide large amounts of biomass but are hardly mentioned in the debates. Harvesting reed does not threaten the nature and the natural functions of reed lands, which are carbon neutral or carbon dioxide sinks. Reed production does not need extensive infrastructure or complex cultivation and does not compete with food production for land and fresh water. Reed lands in many places are under threat of reclamation for economic activities and urbanisation. This trend can be countered if reed is seen to have a proven economic value. In this article I argue that giving a sustainable economic value to reed lands can only be realised if the exploitation is recognised as being environmentally acceptable, commercially feasible and a source of economic gains for all stakeholders. Commercial feasibility can be achieved under present economic conditions only if a reliable supply of considerable volumes of reed at a limited price can be guaranteed.

  17. Magma chamber interaction giving rise to asymmetric oscillations

    Science.gov (United States)

    Walwer, D.; Ghil, M.; Calais, E.

    2017-12-01

    Geodetic time series at four volcanoes (Okmok, Akutan, Shishaldin, and Réunion) are processed using Multi-channel Singular Spectrum Analysis (M-SSA) and reveal sawtooth-shaped oscillations ; the latter are characterized by short intervals of fast inflations followed by longer intervals of slower deflations. At Okmok and Akutan, the oscillations are first damped and then accentuated. At Okmok, the increase in amplitude of the oscillations is followed by an eruption. We first show that the dynamics of these four volcanoes bears similarities with that of a simple nonlinear, dissipative oscillator, indicating that the inflation-deflation episodes are relaxation oscillations. These observations imply that ab initio dynamical models of magma chambers should possess an asymmetric oscillatory regime. Next, based on the work of Whitehead and Helfrich [1991], we show that a model of two magma chambers — connected by a cylindrical conduit in which the magma viscosity depends on temperature — gives rise to asymmetric overpressure oscillations in the magma reservoirs. These oscillations lead to surface deformations that are consistent with those observed at the four volcanoes in this study. This relaxation oscillation regime occurs only when the vertical temperature gradient in the host rock between the two magma chambers is large enough and when the magma flux entering the volcanic system is sufficiently high. The magma being supplied by a deeper source region, the input flux depends on the pressure difference between the source and the deepest reservoir. When this difference is not sufficiently high, the magma flux exponentially decreases, leading to damped oscillations as observed at Akutan and Okmok. The combination of observational and modeling results clearly supports the role of relaxation oscillations in the dynamics of volcanic systems.

  18. Pumping slots: Coupling impedance calculations and estimates

    International Nuclear Information System (INIS)

    Kurennoy, S.

    1993-08-01

    Coupling impedances of small pumping holes in vacuum-chamber walls have been calculated at low frequencies, i.e., for wavelengths large compared to a typical hole size, in terms of electric and magnetic polarizabilities of the hole. The polarizabilities can be found by solving and electro- or magnetostatic problem and are known analytically for the case of the elliptic shape of the hole in a thin wall. The present paper studies the case of pumping slots. Using results of numerical calculations and analytical approximations of polarizabilities, we give formulae for practically important estimates of slot contribution to low-frequency coupling impedances

  19. Precise calculations of the deuteron quadrupole moment

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Franz L. [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

    2016-06-01

    Recently, two calculations of the deuteron quadrupole moment have have given predictions that agree with the measured value to within 1%, resolving a long-standing discrepancy. One of these uses the covariant spectator theory (CST) and the other chiral effective field theory (cEFT). In this talk I will first briefly review the foundations and history of the CST, and then compare these two calculations with emphasis on how the same physical processes are being described using very different language. The comparison of the two methods gives new insights into the dynamics of the low energy NN interaction.

  20. Conformal mapping calculation of railgun skin inductance

    International Nuclear Information System (INIS)

    Huerta, M.A.; Nearing, J.C.

    1991-01-01

    This paper considers the common rail arrangement consisting of two long, parallel, rectangular rails. The authors calculate the inductance per unit length L' in the short flight time limit where the skin depth is much smaller than any rail dimensions, the current is all on the rail surface, and the magnetic field does not penetrate the rails. The authors give the solution based on the Schwartz-Christoffel transformation that maps the boundaries of the problem into a simpler shape

  1. Dose calculation for electrons

    International Nuclear Information System (INIS)

    Hirayama, Hideo

    1995-01-01

    The joint working group of ICRP/ICRU is advancing the works of reviewing the ICRP publication 51 by investigating the data related to radiation protection. In order to introduce the 1990 recommendation, it has been demanded to carry out calculation for neutrons, photons and electrons. As for electrons, EURADOS WG4 (Numerical Dosimetry) rearranged the data to be calculated at the meeting held in PTB Braunschweig in June, 1992, and the question and request were presented by Dr. J.L. Chartier, the responsible person, to the researchers who are likely to undertake electron transport Monte Carlo calculation. The author also has carried out the requested calculation as it was the good chance to do the mutual comparison among various computation codes regarding electron transport calculation. The content that the WG requested to calculate was the absorbed dose at depth d mm when parallel electron beam enters at angle α into flat plate phantoms of PMMA, water and ICRU4-element tissue, which were placed in vacuum. The calculation was carried out by the versatile electron-photon shower computation Monte Carlo code, EGS4. As the results, depth dose curves and the dependence of absorbed dose on electron energy, incident angle and material are reported. The subjects to be investigated are pointed out. (K.I.)

  2. Radioactive cloud dose calculations

    International Nuclear Information System (INIS)

    Healy, J.W.

    1984-01-01

    Radiological dosage principles, as well as methods for calculating external and internal dose rates, following dispersion and deposition of radioactive materials in the atmosphere are described. Emphasis has been placed on analytical solutions that are appropriate for hand calculations. In addition, the methods for calculating dose rates from ingestion are discussed. A brief description of several computer programs are included for information on radionuclides. There has been no attempt to be comprehensive, and only a sampling of programs has been selected to illustrate the variety available

  3. Spin beam splitter based on Goos-Haenchen shifts in two-dimensional electron gas modulated by ferromagnetic and Schottky metal stripes

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Mao-Wang; Huang, Xin-Hong; Zhang, Gui-Lin; Chen, Sai-Yan [College of Science, Guilin University of Technology, Guilin 541004 (China)

    2012-11-15

    We present a theoretical study on the spin-dependent Goos-Haenchen (GH) effect in a two-dimensional electron gas modulated by ferromagnetic and Schottky metal (SM) stripes. The GH shifts for spin electron beams across this device are calculated with the help of the stationary phase method. It is shown that the GH shift of spin-up beam is significantly different from that of spin-down beam, i.e., this device shows up a considerable spin polarization effect in GH shifts of electron beams. It also is shown that both magnitude and sign of spin polarization of GH shifts are closely related to the stripe width, the magnetic strength and the gated voltage under SM stripe. These interesting properties not only provide an effective method of spin injection for spintronics application, but also give rise to a tunable spin beam splitter. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Rotor calculations for neutron spectroscopy; Calculs des rotors de spectrometres a neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Gobert, G. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1968-07-01

    The determination of stress in a rotating disk plane of symmetry normal to the axis of rotation has been studied by a number of investigators. In a recent paper Reich gives an operating process for an analytical solution in an asymmetric rotating disk. In the report we give the calculation of finite difference stress solutions applicable to the two rotating disks. The equations are then programmed for the 360.75 computer by Fortran methods concerning the rotors of choppers. (author) [French] La determination des contraintes dans les disques symetriques, en rotation a ete etudiee par de nombreux auteurs. Dans un recent rapport, Reich donne une solution pour le calcul des disques asymetriques. Ce rapport concerne l'application du calcul des contraintes par differences finies aux deux types de rotors. Les equations ecrites en langage Fortran pour l'ordinateur 360.75 concerne les rotors de choppers. (auteur)

  5. GIVE THE PUBLIC SOMETHING, SOMETHING MORE INTERESTING THAN RADIOACTIVE WASTE

    International Nuclear Information System (INIS)

    Codee, Hans D.K.

    2003-01-01

    In the Netherlands the policy to manage radioactive waste is somewhat different from that in other countries, although the practical outcome is not much different. Long-term, i.e. at least 100 years, storage in above ground engineered structures of all waste types is the first element in the Dutch policy. Second element, but equally important, is that deep geologic disposal is foreseen after the storage period. This policy was brought out in the early eighties and was communicated to the public as a practical, logical and feasible management system for the Dutch situation. Strong opposition existed at that time to deep disposal in salt domes in the Netherlands. Above ground storage at principle was not rejected because the need to do something was obvious. Volunteers for a long term storage site did not automatically emerge. A site selection procedure was followed and resulted in the present site at Vlissingen-Oost. The waste management organization, COVRA, was not really welcomed here , but was tolerated. In the nineties facilities for low and medium level waste were erected and commissioned. In the design of the facilities much attention was given to emotional factors. The first ten operational years were needed to gain trust from the local population. Impeccable conduct and behavior was necessary as well as honesty and full openness to the public Now, after some ten years, the COVRA facilities are accepted. And a new phase is entered with the commissioning of the storage facility for high level waste, the HABOG facility. A visit to that facility will not be very spectacular, activities take place only during loading and unloading. Furthermore it is a facility for waste, so unwanted material will be brought into the community. In order to give the public something more interesting the building itself is transformed into a piece of art and in the inside a special work of art will be displayed. Together with that the attitude of the company will change. We are

  6. Small portable speed calculator

    Science.gov (United States)

    Burch, J. L.; Billions, J. C.

    1973-01-01

    Calculator is adapted stopwatch calibrated for fast accurate measurement of speeds. Single assembled unit is rugged, self-contained, and relatively inexpensive to manufacture. Potential market includes automobile-speed enforcement, railroads, and field-test facilities.

  7. Unit Cost Compendium Calculations

    Data.gov (United States)

    U.S. Environmental Protection Agency — The Unit Cost Compendium (UCC) Calculations raw data set was designed to provide for greater accuracy and consistency in the use of unit costs across the USEPA...

  8. Magnetic Field Grid Calculator

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Properties Calculator will computes the estimated values of Earth's magnetic field(declination, inclination, vertical component, northerly...

  9. National Stormwater Calculator

    Science.gov (United States)

    EPA’s National Stormwater Calculator (SWC) is a desktop application that estimates the annual amount of rainwater and frequency of runoff from a specific site anywhere in the United States (including Puerto Rico).

  10. Stormwater Calculator (SWC) webinar

    Science.gov (United States)

    Jason Berner presents EPA’s National Stormwater Calculator developed to help support local, state and national stormwater management objectives and regulatory efforts to reduce runoff using green infrastructure practices as low impact development controls.

  11. Current interruption transients calculation

    CERN Document Server

    Peelo, David F

    2014-01-01

    Provides an original, detailed and practical description of current interruption transients, origins, and the circuits involved, and how they can be calculated Current Interruption Transients Calculationis a comprehensive resource for the understanding, calculation and analysis of the transient recovery voltages (TRVs) and related re-ignition or re-striking transients associated with fault current interruption and the switching of inductive and capacitive load currents in circuits. This book provides an original, detailed and practical description of current interruption transients, origins,

  12. Fast focus field calculations

    OpenAIRE

    Leutenegger, M.; Rao, R.; Leitgeb, R. A.; Lasser, T.

    2006-01-01

    We present a fast calculation of the electromagnetic field near the focus of an objective with a high numerical aperture (NA). Instead of direct integration, the vectorial Debye diffraction integral is evaluated with the fast Fourier transform for calculating the electromagnetic field in the entire focal region. We generalize this concept with the chirp z transform for obtaining a flexible sampling grid and an additional gain in computation speed. Under ...

  13. Quantum Chemical Calculations

    Science.gov (United States)

    Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)

    1997-01-01

    The current methods of quantum chemical calculations will be reviewed. The accent will be on the accuracy that can be achieved with these methods. The basis set requirements and computer resources for the various methods will be discussed. The utility of the methods will be illustrated with some examples, which include the calculation of accurate bond energies for SiF$_n$ and SiF$_n^+$ and the modeling of chemical data storage.

  14. Validation of dose calculation programmes for recycling

    Energy Technology Data Exchange (ETDEWEB)

    Menon, Shankar [Menon Consulting, Nykoeping (Sweden); Brun-Yaba, Christine [Inst. de Radioprotection et Securite Nucleaire (France); Yu, Charley; Cheng, Jing-Jy [Argonne National Laboratory, IL (United States). Environmental Assessment Div.; Bjerler, Jan [Studsvik Stensand, Nykoeping (Sweden); Williams, Alexander [Dept. of Energy (United States). Office of Environmental Management

    2002-12-01

    This report contains the results from an international project initiated by the SSI in 1999. The primary purpose of the project was to validate some of the computer codes that are used to estimate radiation doses due to the recycling of scrap metal. The secondary purpose of the validation project was to give a quantification of the level of conservatism in clearance levels based on these codes. Specifically, the computer codes RESRAD-RECYCLE and CERISE were used to calculate radiation doses to individuals during the processing of slightly contaminated material, mainly in Studsvik, Sweden. Calculated external doses were compared with measured data from different steps of the process. The comparison of calculations and measurements shows that the computer code calculations resulted in both overestimations and underestimations of the external doses for different recycling activities. The SSI draws the conclusion that the accuracy is within one order of magnitude when experienced modellers use their programmes to calculate external radiation doses for a recycling process involving material that is mainly contaminated with cobalt-60. No errors in the codes themselves were found. Instead, the inaccuracy seems to depend mainly on the choice of some modelling parameters related to the receptor (e.g., distance, time, etc.) and simplifications made to facilitate modelling with the codes (e.g., object geometry). Clearance levels are often based on studies on enveloping scenarios that are designed to cover all realistic exposure pathways. It is obvious that for most practical cases, this gives a margin to the individual dose constraint (in the order of 10 micro sievert per year within the EC). This may be accentuated by the use of conservative assumptions when modelling the enveloping scenarios. Since there can obviously be a fairly large inaccuracy in the calculations, it seems reasonable to consider some degree of conservatism when establishing clearance levels based on

  15. Numerical challenges of short range wake field calculations

    Energy Technology Data Exchange (ETDEWEB)

    Lau, Thomas; Gjonaj, Erion; Weiland, Thomas [Technische Universitaet Darmstadt (Germany). Institut fuer Theorie Elektromagnetischer Felder (TEMF)

    2011-07-01

    For present and future accelerator projects with ultra short bunches the accurate and reliable calculation of short range wake fields is an important issue. However, the numerical calculation of short range wake fields is a numerical challenging task. The presentation gives an overview over the numerical challenges and techniques for short range wake field calculations. Finally, some simulation results obtained by the program PBCI developed at the TU Darmstadt are presented.

  16. Evolution of calculation methods taking into account severe accidents

    International Nuclear Information System (INIS)

    L'Homme, A.; Courtaud, J.M.

    1990-12-01

    During the first decade of PWRs operation in France the calculation methods used for design and operation have improved very much. This paper gives a general analysis of the calculation methods evolution in parallel with the evolution of safety approach concerning PWRs. Then a comprehensive presentation of principal calculation tools is presented as applied during the past decade. An effort is done to predict the improvements in near future

  17. ON-LINE CALCULATOR: FORWARD CALCULATION JOHNSON ETTINGER MODEL

    Science.gov (United States)

    On-Site was developed to provide modelers and model reviewers with prepackaged tools ("calculators") for performing site assessment calculations. The philosophy behind OnSite is that the convenience of the prepackaged calculators helps provide consistency for simple calculations,...

  18. Uncertainty calculations made easier

    International Nuclear Information System (INIS)

    Hogenbirk, A.

    1994-07-01

    The results are presented of a neutron cross section sensitivity/uncertainty analysis performed in a complicated 2D model of the NET shielding blanket design inside the ITER torus design, surrounded by the cryostat/biological shield as planned for ITER. The calculations were performed with a code system developed at ECN Petten, with which sensitivity/uncertainty calculations become relatively simple. In order to check the deterministic neutron transport calculations (performed with DORT), calculations were also performed with the Monte Carlo code MCNP. Care was taken to model the 2.0 cm wide gaps between two blanket segments, as the neutron flux behind the vacuum vessel is largely determined by neutrons streaming through these gaps. The resulting neutron flux spectra are in excellent agreement up to the end of the cryostat. It is noted, that at this position the attenuation of the neutron flux is about 1 l orders of magnitude. The uncertainty in the energy integrated flux at the beginning of the vacuum vessel and at the beginning of the cryostat was determined in the calculations. The uncertainty appears to be strongly dependent on the exact geometry: if the gaps are filled with stainless steel, the neutron spectrum changes strongly, which results in an uncertainty of 70% in the energy integrated flux at the beginning of the cryostat in the no-gap-geometry, compared to an uncertainty of only 5% in the gap-geometry. Therefore, it is essential to take into account the exact geometry in sensitivity/uncertainty calculations. Furthermore, this study shows that an improvement of the covariance data is urgently needed in order to obtain reliable estimates of the uncertainties in response parameters in neutron transport calculations. (orig./GL)

  19. Online plasma calculator

    Science.gov (United States)

    Wisniewski, H.; Gourdain, P.-A.

    2017-10-01

    APOLLO is an online, Linux based plasma calculator. Users can input variables that correspond to their specific plasma, such as ion and electron densities, temperatures, and external magnetic fields. The system is based on a webserver where a FastCGI protocol computes key plasma parameters including frequencies, lengths, velocities, and dimensionless numbers. FastCGI was chosen to overcome security problems caused by JAVA-based plugins. The FastCGI also speeds up calculations over PHP based systems. APOLLO is built upon the WT library, which turns any web browser into a versatile, fast graphic user interface. All values with units are expressed in SI units except temperature, which is in electron-volts. SI units were chosen over cgs units because of the gradual shift to using SI units within the plasma community. APOLLO is intended to be a fast calculator that also provides the user with the proper equations used to calculate the plasma parameters. This system is intended to be used by undergraduates taking plasma courses as well as graduate students and researchers who need a quick reference calculation.

  20. Giving USA 1997: The Annual Report on Philanthropy for the Year 1996.

    Science.gov (United States)

    Kaplan, Ann E., Ed.

    This report presents a comprehensive review of private philanthropy in the United States during 1996. After a preliminary section, the first section presents data on giving, using text, graphs, and charts. Sections cover: overall 1996 contributions; changes in giving by source and use; total giving (1966-1996); inflation-adjusted giving in 5-year…

  1. LHC Bellows Impedance Calculations

    CERN Document Server

    Dyachkov, M

    1997-01-01

    To compensate for thermal expansion the LHC ring has to accommodate about 2500 bellows which, together with beam position monitors, are the main contributors to the LHC broad-band impedance budget. In order to reduce this impedance to an acceptable value the bellows have to be shielded. In this paper we compare different designs proposed for the bellows and calculate their transverse and longitudinal wakefields and impedances. Owing to the 3D geometry of the bellows, the code MAFIA was used for the wakefield calculations; when possible the MAFIA results were compared to those obtained with ABCI. The results presented in this paper indicate that the latest bellows design, in which shielding is provided by sprung fingers which can slide along the beam screen, has impedances smaller tha those previously estimated according to a rather conservative scaling of SSC calculations and LEP measurements. Several failure modes, such as missing fingers and imperfect RF contact, have also been studied.

  2. Calculating Quenching Weights

    CERN Document Server

    Salgado, C A; Salgado, Carlos A.; Wiedemann, Urs Achim

    2003-01-01

    We calculate the probability (``quenching weight'') that a hard parton radiates an additional energy fraction due to scattering in spatially extended QCD matter. This study is based on an exact treatment of finite in-medium path length, it includes the case of a dynamically expanding medium, and it extends to the angular dependence of the medium-induced gluon radiation pattern. All calculations are done in the multiple soft scattering approximation (Baier-Dokshitzer-Mueller-Peign\\'e-Schiff--Zakharov ``BDMPS-Z''-formalism) and in the single hard scattering approximation (N=1 opacity approximation). By comparison, we establish a simple relation between transport coefficient, Debye screening mass and opacity, for which both approximations lead to comparable results. Together with this paper, a CPU-inexpensive numerical subroutine for calculating quenching weights is provided electronically. To illustrate its applications, we discuss the suppression of hadronic transverse momentum spectra in nucleus-nucleus colli...

  3. Note about socio-economic calculations

    DEFF Research Database (Denmark)

    Landex, Alex; Andersen, Jonas Lohmann Elkjær; Salling, Kim Bang

    2006-01-01

    This note gives a short introduction of how to make socio-economic evaluations in connection with the teaching at the Centre for Traffic and Transport (CTT). It is not a manual for making socio-economic calculations in transport infrastructure projects – in this context we refer to the guidelines...... for socio-economic calculations within the transportation area (Ministry of Traffic, 2003). The note also explains the theory of socio-economic calculations – reference is here made to ”Road Infrastructure Planning – a Decision-oriented approach” (Leleur, 2000). Socio-economic evaluations of infrastructure...... projects are common and can be made at different levels of detail depending on the type of project and the decision making phase. A common feature of the different levels of detail of the socio-economic analysis is that the planned project(s) is compared with a basic; the basic alternative or a null...

  4. Execution gives the recommendations given by WAMAP to Guatemala in relation to the administration he/she gives the radioactive waste

    International Nuclear Information System (INIS)

    Gomez Ordonnez, P.

    1998-01-01

    The Wamap mission visits Guatemala assisting to application Direccion General de Energia. The nuclear activity in Guatemala is limited to the investigation and the radioisotopes application. In this visit three important aspects were identified that required attention: The establishment gives a Regulatory law in the handling waste; An inventory gives the radioactive waste that have been generated; Technical knowledge on the storage. gathering and immobilization gives the waste

  5. Nuclear spin polarized alkali beams (Li and Na): Production and acceleration

    International Nuclear Information System (INIS)

    Jaensch, H.; Becker, K.; Blatt, K.; Leucker, H.; Fick, D.

    1987-01-01

    Recent improvements of the Heidelberg source for polarized heavy ions (PSI) are described. By means of optical pumping in combination with the existing multipole separation magnet the beam figure of merit (polarization 2 x intensity) was doubled. 7 Li and 23 Na atomic beams can now be produced in pure hyperfine magnetic substates. Fast switching of the polarization is achieved by an adiabatic medium field transition. The hyperfine magnetic substate population is determined by laser-induced fluorescence spectroscopy. In routine operation atomic beams with nuclear polarization p α ≥0.85 (α=z, zz) are obtained. The acceleration of polarized 23 Na - ions by a 12 MV tandem accelerator introduces a new problem: the energy at the terminal stripper foil is not sufficient to produce a usable yield of naked ions. For partially stripped ions hyperfine interaction of the remaining electrons with the nuclear spin reduces the nuclear polarization. Using in addition the Heidelberg postaccelerator 23 Na 9+ beams of energies between 49 and 184 MeV were obtained with an alignment on target of P zz ≅0.45. 7 Li beams have also been accelerated up to 45 MeV with an alignment of P zz =0.69. (orig.)

  6. Shot noise as a probe of spin-polarized transport through single atoms

    DEFF Research Database (Denmark)

    Burtzlaff, Andreas; Weismann, Alexander; Brandbyge, Mads

    2015-01-01

    Single atoms on Au(111) surfaces have been contacted with the Au tip of a low temperature scanning tunneling microscope. The shot noise of the current through these contacts has been measured up to frequencies of 120 kHz and Fano factors have been determined to characterize the transport channels...

  7. Effect of orbital hybridization on spin-polarized tunneling across Co/C60 interfaces

    NARCIS (Netherlands)

    Wang, Kai; Strambini, Elia; Sanderink, Johannes G.M.; Bolhuis, Thijs; van der Wiel, Wilfred Gerard; de Jong, Machiel Pieter

    2016-01-01

    The interaction between ferromagnetic surfaces and organic semiconductors leads to the formation of hybrid interfacial states. As a consequence, the local magnetic moment is altered, a hybrid interfacial density of states (DOS) is formed, and spin-dependent shifts of energy levels occur. Here, we

  8. Spin-polarized transport properties of a pyridinium-based molecular spintronics device

    Science.gov (United States)

    Zhang, J.; Xu, B.; Qin, Z.

    2018-05-01

    By applying a first-principles approach based on non-equilibrium Green's functions combined with density functional theory, the transport properties of a pyridinium-based "radical-π-radical" molecular spintronics device are investigated. The obvious negative differential resistance (NDR) and spin current polarization (SCP) effect, and abnormal magnetoresistance (MR) are obtained. Orbital reconstruction is responsible for novel transport properties such as that the MR increases with bias and then decreases and that the NDR being present for both parallel and antiparallel magnetization configurations, which may have future applications in the field of molecular spintronics.

  9. Beamline for Photoemission Spectromicroscopy and Spin Polarized Microscopy with Slow Electrons at CESLAB

    Czech Academy of Sciences Publication Activity Database

    Frank, Luděk

    2008-01-01

    Roč. 15, č. 1 (2008), s. 111-112 ISSN 1210-8529 Institutional research plan: CEZ:AV0Z20650511 Keywords : CESLAB * beamline * LEEM/PEEM Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  10. Study of mechanical compression of spin-polarized 3He gas

    International Nuclear Information System (INIS)

    Becker, J.; Heil, W.; Krug, B.; Leduc, M.; Meyerhoff, M.; Nacher, P.J.; Otten, E.W.; Prokscha, T.; Schearer, L.D.; Surkau, R.

    1994-01-01

    We have piloted mechanical compression of spinpolarized 3He by a titanium piston compressor. Questions of materials and design are discussed, followed by a thorough investigation of relaxation sources in the course of compression. The latter are traced mainly to regions with large surface to volume ratio, through which fast passage is demanded, therefore. We conclude from this feasibility study that polarized 3He may be compressed this way up to many bars without serious polarization losses. ((orig.))

  11. Manipulating NiFe/AlOx interfacial chemistry for the spin-polarized electrons transport

    International Nuclear Information System (INIS)

    Zhao, Chong-Jun; Sun, Li; Ding, Lei; Li, Jian-Wei; Zhang, Jing-Yan; Cao, Yi; Yu, Guang-Hua

    2013-01-01

    Through vacuum annealing, interfacial chemical composition of sputter-deposited AlO x /NiFe/AlO x can be controlled for electron transport manipulation. Chemical status change at the NiFe/AlO x interface was quantified by X-ray photoelectron spectroscopy and correlated to the structure and electron transport properties of the heterostructure. It is found that elemental Al existed in the insulting AlO x after annealing at intermediate temperature can improve the AlO x /NiFe interface and thus favor the electronic transport. Annealing at higher temperature will result in native AlO x formation and degrade transport properties due to the NiFe/AlO x interfaces deterioration caused by significant difference in thermal expansion coefficients of the two materials.

  12. Spin polarization in high density quark matter under a strong external magnetic field

    DEFF Research Database (Denmark)

    Tsue, Yasuhiko; Da Providência, João; Providência, Constança

    2016-01-01

    In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor-type interact......In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor...... phase appears in the wide range of the quark chemical potential. In both the interactions, the quark mass in zero and small chemical potential regions increases which indicates that the chiral symmetry breaking is enhanced, namely the magnetic catalysis occurs....

  13. Voltage switching technique for detecting nuclear spin polarization in a quantum dot

    International Nuclear Information System (INIS)

    Takahashi, Ryo; Kono, Kimitoshi; Tarucha, Seigo; Ono, Keiji

    2010-01-01

    We have introduced a source-drain voltage switching technique for studying nuclear spins in a vertical double quantum dot. Switching the source-drain voltage between the spin-blockade state and the zero-bias Coulomb blockade state can tune the energy difference between the spin singlet and triplet, and effectively turn on/off the hyperfine interaction. Since the change in the nuclear spin state affects the source-drain current, nuclear spin properties can only be detected by transport measurement. Using this technique, we have succeeded in measuring the timescale of nuclear spin depolarization. Furthermore, combining this technique and an RF ac magnetic field, we successfully detected continuous-wave NMR signals of 75 As, 69 Ga, and 71 Ga, which are contained in a quantum dot. (author)

  14. A laser driven source of spin polarized atomic hydrogen and deuterium

    International Nuclear Information System (INIS)

    Poelker, M.; Coulter, K.P.; Holt, R.J.; Jones, C.E.; Kowalczyk, R.S.; Young, L.; Toporkov, D.

    1993-01-01

    Recent results from a laser-driven source of polarized hydrogen (H) and deuterium (D) are presented. The performance of the source is described as a function of atomic flow rate and magnetic field. The data suggest that because atomic densities in the source are high, the system can approach spin-temperature equilibrium although applied magnetic fields are much larger than the critical field of the atoms. The authors also observe that potassium contamination in the source emittance can be reduced to a negligible amount using a teflon-lined transport tube

  15. Single-Spin Polarization Effects and the Determination of Timelike Proton Form Factors

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, S

    2003-10-24

    We show that measurements of the proton's polarization in e{sup +}e{sup -} {yields} p{bar p} strongly discriminate between analytic forms of models which fit the proton form factors in the spacelike region. In particular, the single-spin asymmetry normal to the scattering plane measures the relative phase difference between the timelike G{sub E} and G{sub M} form factors. The expected proton polarization in the timelike region is large, of order of several tens of percent.

  16. Bounds on the maximum attainable equilibrium spin polarization of protons at high energy in HERA

    International Nuclear Information System (INIS)

    Vogt, M.

    2000-12-01

    For some years HERA has been supplying longitudinally spin polarised electron and positron (e ± ) beams to the HERMES experiment and in the future longitudinal polarisation will be supplied to the II1 and ZEUS experiments. As a result there has been a development of interest in complementing the polarised e ± beams with polarised protons. In contrast to the case of e ± where spin flip due to synchrotron radiation in the main bending dipoles leads to self polarisation owing to an up-down asymmetry in the spin flip rates (Sokolov-Ternov effect), there is no convincing self polarisation mechanism for protons at high energy. Therefore protons must be polarised almost at rest in a source and then accelerated to the working energy. At HERA, if no special measures are adopted, this means that the spins must cross several thousand ''spin-orbit resonances''. Resonance crossing can lead to loss of polarisation and at high energy such effects are potentially strong since spin precession is very pronounced in the very large magnetic fields needed to contain the proton beam in HERA-p. Moreover simple models which have been successfully used to describe spin motion at low and medium energies are no longer adequate. Instead, careful numerical spin-orbit tracking simulations are needed and a new, mathematically rigorous look at the theoretical concepts is required. This thesis describes the underlying theoretical concepts, the computational tools (SPRINT) and the results of such a study. In particular strong emphasis is put on the concept of the invariant spin field and its non-perturbative construction. The invariant spin field is then used to define the amplitude dependent spin tune and to obtain numerical non-perturbative estimates of the latter. By means of these two key concepts the nature of higher order resonances in the presence of snakes is clarified and their impact on the beam polarisation is analysed. We then go on to discuss the special aspects of the HERA-p ring and measures for minimising the perturbations to the spin motion (→ depolarisation) and thereby obtain first upper bounds on the permissible beam emittances needed to maintain polarisation up to high energy in HERA-p. (orig.)

  17. Calculating magnetohydrodynamic flow spectra

    NARCIS (Netherlands)

    Nijboer, R. J.; van der Holst, B.; Poedts, S.; Goedbloed, J. P.

    1997-01-01

    We describe a numerical method for calculating the magnetohydrodynamic (MHD) spectrum of one-dimensional equilibria with Bow. Due to a general formulation, the spectrum for two different equilibrium geometries, viz. a plane slab and a cylinder, can be investigated. The linearised equations are

  18. Languages for structural calculations

    International Nuclear Information System (INIS)

    Thomas, J.B.; Chambon, M.R.

    1988-01-01

    The differences between human and computing languages are recalled. It is argued that they are to some extent structured in antagonistic ways. Languages in structural calculation, in the past, present, and future, are considered. The contribution of artificial intelligence is stressed [fr

  19. Monte Carlo alpha calculation

    Energy Technology Data Exchange (ETDEWEB)

    Brockway, D.; Soran, P.; Whalen, P.

    1985-01-01

    A Monte Carlo algorithm to efficiently calculate static alpha eigenvalues, N = ne/sup ..cap alpha..t/, for supercritical systems has been developed and tested. A direct Monte Carlo approach to calculating a static alpha is to simply follow the buildup in time of neutrons in a supercritical system and evaluate the logarithmic derivative of the neutron population with respect to time. This procedure is expensive, and the solution is very noisy and almost useless for a system near critical. The modified approach is to convert the time-dependent problem to a static ..cap alpha../sup -/eigenvalue problem and regress ..cap alpha.. on solutions of a/sup -/ k/sup -/eigenvalue problem. In practice, this procedure is much more efficient than the direct calculation, and produces much more accurate results. Because the Monte Carlo codes are intrinsically three-dimensional and use elaborate continuous-energy cross sections, this technique is now used as a standard for evaluating other calculational techniques in odd geometries or with group cross sections.

  20. Cooling tower calculations

    International Nuclear Information System (INIS)

    Simonkova, J.

    1988-01-01

    The problems are summed up of the dynamic calculation of cooling towers with forced and natural air draft. The quantities and relations are given characterizing the simultaneous exchange of momentum, heat and mass in evaporative water cooling by atmospheric air in the packings of cooling towers. The method of solution is clarified in the calculation of evaporation criteria and thermal characteristics of countercurrent and cross current cooling systems. The procedure is demonstrated of the calculation of cooling towers, and correction curves and the effect assessed of the operating mode at constant air number or constant outlet air volume flow on their course in ventilator cooling towers. In cooling towers with the natural air draft the flow unevenness is assessed of water and air relative to its effect on the resulting cooling efficiency of the towers. The calculation is demonstrated of thermal and resistance response curves and cooling curves of hydraulically unevenly loaded towers owing to the water flow rate parameter graded radially by 20% along the cross-section of the packing. Flow rate unevenness of air due to wind impact on the outlet air flow from the tower significantly affects the temperatures of cooled water in natural air draft cooling towers of a design with lower demands on aerodynamics, as early as at wind velocity of 2 m.s -1 as was demonstrated on a concrete example. (author). 11 figs., 10 refs