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Sample records for absorption magnetic circular

  1. X-ray absorption and magnetic circular dichroism studies of Co2FeAl in magnetic tunnel junctions

    SciTech Connect

    Ebke, D.; Kugler, Z.; Thomas, P.; Schebaum, O.; Schafers, M.; Nissen, D.; Schmalhorst, J.; Hutten, A.; Arenholz, E.; Thomas, A.

    2010-01-11

    The bulk magnetic moment and the element specific magnetic moment of Co{sub 2}FeAl thin films were examined as a function of annealing temperature by alternating gradient magnetometer (AGM) and X-ray absorption spectroscopy (XAS)/X-ray magnetic circular dichroism (XMCD), respectively. A high magnetic moment can be achieved for all annealing temperatures and the predicted bulk and interface magnetic moment of about 5 {tilde A}{sub B} are reached via heating. We will also present tunnel magnetoresistance (TMR) values of up to 153% at room temperature and 260% at 13 K for MgO based magnetic tunnel junctions (MTJs) with Co{sub 2}FeAl and Co-Fe electrodes.

  2. Observation of x-ray absorption magnetic circular dichroism in well-characterized iron-cobalt-platinum multilayers

    SciTech Connect

    Jankowski, A.F.; Waddill, G.D.; Tobin, J.G.

    1993-04-01

    Magnetic circular dichroism in the Fe 2p x-ray absorption is observed in multilayers of(Fe9.5{Angstrom}/Pt9.5{Angstrom}){sub 92}. The magnetization and helicity are both in the plane of this multilayer which is prepared by magnetron sputter deposition. This sample is part of a study to examine magnetization in the ternary multilayer system of FeCo/Pt. Lattice and layer pair spacings are measured using x-ray scattering. The atomic concentration profiles of the multilayer films are characterized using Auger electron spectroscopy coupled with depth profiling. Conventional and high resolution transmission electron microscopy are used to examine the thin film, growth morphology and atomic structure.

  3. X-ray absorption spectroscopy and magnetic circular dichroism studies of L1{sub 0}-Mn-Ga thin films

    SciTech Connect

    Glas, M. Sterwerf, C.; Schmalhorst, J. M.; Reiss, G.; Ebke, D.; Jenkins, C.; Arenholz, E.

    2013-11-14

    Tetragonally distorted Mn{sub 3−x}Ga{sub x} thin films with 0.1magnetic anisotropy and low magnetization and thus have the potential to serve as electrodes in spin transfer torque magnetic random access memory. Because a direct capping of these films with MgO is problematic due to oxide formation, we examined the influence of a CoFeB interlayer and of two different deposition methods for the MgO barrier on the formation of interfacial Mn-O for Mn{sub 62}Ga{sub 38} by element specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). A highly textured L1{sub 0} crystal structure of the Mn-Ga films was verified by X-ray diffraction measurements. For samples with e-beam evaporated MgO barrier no evidence for Mn-O was found whereas in samples with magnetron sputtered MgO, Mn-O was detected, even for the thickest interlayer thickness. Both XAS and XMCD measurements showed an increasing interfacial Mn-O amount with decreasing CoFeB interlayer thickness. Additional element specific full hysteresis loops determined an out-of-plane magnetization axis for the Mn and Co, respectively.

  4. Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser.

    PubMed

    Higley, Daniel J; Hirsch, Konstantin; Dakovski, Georgi L; Jal, Emmanuelle; Yuan, Edwin; Liu, Tianmin; Lutman, Alberto A; MacArthur, James P; Arenholz, Elke; Chen, Zhao; Coslovich, Giacomo; Denes, Peter; Granitzka, Patrick W; Hart, Philip; Hoffmann, Matthias C; Joseph, John; Le Guyader, Loïc; Mitra, Ankush; Moeller, Stefan; Ohldag, Hendrik; Seaberg, Matthew; Shafer, Padraic; Stöhr, Joachim; Tsukamoto, Arata; Nuhn, Heinz-Dieter; Reid, Alex H; Dürr, Hermann A; Schlotter, William F

    2016-03-01

    X-ray magnetic circular dichroism spectroscopy using an X-ray free electron laser is demonstrated with spectra over the Fe L(3,2)-edges. The high brightness of the X-ray free electron laser combined with high accuracy detection of incident and transmitted X-rays enables ultrafast X-ray magnetic circular dichroism studies of unprecedented sensitivity. This new capability is applied to a study of all-optical magnetic switching dynamics of Fe and Gd magnetic sublattices in a GdFeCo thin film above its magnetization compensation temperature. PMID:27036761

  5. Disentanglement of magnetic contributions in multi-component systems by using X-ray magnetic circular dichroism at a single absorption edge.

    PubMed

    Chaboy, Jesús; Laguna-Marco, María Angeles; Piquer, Cristina; Boada, Roberto; Maruyama, Hiroshi; Kawamura, Naomi

    2008-09-01

    X-ray magnetic circular dichroism (XMCD) has become in recent years an outstanding tool for studying magnetism. Its element specificity, inherent to core-level spectroscopy, combined with the application of magneto-optical sum rules allows quantitative magnetic measurements at the atomic level. These capabilities are now incorporated as a standard tool for studying the localized magnetism in many systems. However, the application of XMCD to the study of the conduction-band magnetism is not so straightforward. Here, it is shown that the atomic selectivity is not lost when XMCD probes the delocalized states. On the contrary, it provides a direct way of disentangling the magnetic contributions to the conduction band coming from the different elements in the material. This is demonstrated by monitoring the temperature dependence of the XMCD spectra recorded at the rare-earth L(2)-edge in the case of RT(2) (R = rare-earth, T = 3d transition metal) materials. These results open the possibility of performing element-specific magnetometry by using a single X-ray absorption edge.

  6. X-ray magnetic circular dichroism and x-ray absorption spectroscopy of novel magnetic thin films

    SciTech Connect

    Brewer, M.A.; Ju, H.L.; Krishnan, K.M.

    1997-04-01

    The optimization of the magnetic properties of materials for a wide range of applications requires a dynamic iteration between synthesis, property measurements and characterization at appropriate length scales. The authors interest arises both from the increased appreciation of the degree to which magnetic properties can be influenced by tailored microstructures and the ability to characterize them by x-ray scattering/dichroism techniques. Preliminary results of this work at the ALS on `giant` moment in {alpha}{double_prime}-Fe{sub 16}N{sub 2} and `colossal` magnetoresistance in manganite perovskites is presented here. It has recently been claimed that {alpha}{double_prime}-Fe{sub 16}N{sub 2} possesses a giant magnetization of 2.9 T ({approximately}2300 emu/cc) when grown on lattice-matched In{sub 0.2}Ga{sub 0.8}As(001) and Fe/GaAs(001). However, attempts at growth on simpler substrates have resulted in only a modest enhancement in moment and often in multiphase mixtures. Theoretical calculations based on the band structure of Fe{sub 16}N{sub 2} predict values for the magnetization around 2.3 T ({approximately}1780 emu/cc), well below Sugita`s claims, but consistent with the magnetization reported by several other workers. Using appropriate sum rules applied to the integrated MCD spectrum, they hope to determine the magnetic moment of the iron species in the {alpha}{double_prime}-Fe{sub 16}N{sub 2} films and other phases and resolve the orbital and spin contributions to the moment. There is also rapidly growing interest in the `colossal magnetoresistance` effect observed in manganese oxides for both fundamental and commercial applications. To address some of these issues the authors have measured the electron energy loss spectra (EELS) of manganese perovskites at room temperature.

  7. Local electronic states of Fe{sub 4}N films revealed by x-ray absorption spectroscopy and x-ray magnetic circular dichroism

    SciTech Connect

    Ito, Keita; Toko, Kaoru; Suemasu, Takashi; Takeda, Yukiharu; Saitoh, Yuji; Oguchi, Tamio; Kimura, Akio

    2015-05-21

    We performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at Fe L{sub 2,3} and N K-edges for Fe{sub 4}N epitaxial films grown by molecular beam epitaxy. In order to clarify the element specific local electronic structure of Fe{sub 4}N, we compared experimentally obtained XAS and XMCD spectra with those simulated by a combination of a first-principles calculation and Fermi's golden rule. We revealed that the shoulders observed at Fe L{sub 2,3}-edges in the XAS and XMCD spectra were due to the electric dipole transition from the Fe 2p core-level to the hybridization state generated by σ* anti-bonding between the orbitals of N 2p at the body-centered site and Fe 3d on the face-centered (II) sites. Thus, the observed shoulders were attributed to the local electronic structure of Fe atoms at II sites. As to the N K-edge, the line shape of the obtained spectra was explained by the dipole transition from the N 1s core-level to the hybridization state formed by π* and σ* anti-bondings between the Fe 3d and N 2p orbitals. This hybridization plays an important role in featuring the electronic structures and physical properties of Fe{sub 4}N.

  8. Magnetic circular dichroism in EELS (abstract)

    SciTech Connect

    Harp, G.R.; Farrow, R.F.; Marks, R.F.

    1996-04-01

    We evaluate the possibility of using dichroic electron energy loss spectroscopy (DEELS) as an alternative to x-ray magnetic circular dichroism (XMCD). It is well known that electron energy loss spectroscopy and x-ray absorption spectroscopy are highly analogous, providing similar information. A simple semiclassical model suggests that DEELS might have a magnetic sensitivity similar to that of XMCD. This sensitivity will be reduced, however, by multiple scattering of the probe electron before and after the energy loss event. Thus it is difficult to predict the magnitude of the DEELS effect. Experiments were performed at the {ital L}-edge of polycrystalline Fe, Co, and Ni thin film samples with uniaxial in-plane magnetic anisotropy, prepared {ital in} {ital situ} with a magnetic bias field. Even in those most favorable cases, the DEELS effect is seen to be at least 10 times smaller than similar effects in XMCD. {copyright} {ital 1996 American Institute of Physics.}

  9. Theoretical analysis of X-ray magnetic circular dichroism at the Yb L2, 3 absorption edges of YbInCu4 in high magnetic fields around the field-induced valence transition

    NASA Astrophysics Data System (ADS)

    Kotani, A.

    2012-01-01

    High-magnetic-field X-ray absorption spectra (XAS) and its X-ray magnetic circular dichroism (XMCD) at the Yb L2, 3 edges of YbInCu4 are calculated around the field-induced valence transition at about 30 T. The calculations are made by using a new theoretical framework with an extended single impurity Anderson model (SIAM) developed recently by the present author. Two parameters in SIAM, the 4 f level and the hybridization strength, are taken as different values in low- and high-magnetic-field phases of the field-induced valence transition. The calculated results are compared with recent experimental data measured by Matsuda et al. by utilizing a miniature pulsed magnet up to 40 T. The field-dependence of the calculated XMCD spectra is explained in detail on the basis of the field-dependence of the Yb 4 f wavefunctions in the ground state. Some possibilities are discussed on the negative XMCD signal observed experimentally at the L2 edge.

  10. Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism

    PubMed Central

    Fan, Tingting; Grychtol, Patrik; Knut, Ronny; Hernández-García, Carlos; Hickstein, Daniel D.; Zusin, Dmitriy; Gentry, Christian; Dollar, Franklin J.; Mancuso, Christopher A.; Hogle, Craig W.; Kfir, Ofer; Legut, Dominik; Carva, Karel; Ellis, Jennifer L.; Dorney, Kevin M.; Chen, Cong; Shpyrko, Oleg G.; Fullerton, Eric E.; Cohen, Oren; Oppeneer, Peter M.; Milošević, Dejan B.; Becker, Andreas; Jaroń-Becker, Agnieszka A.; Popmintchev, Tenio; Murnane, Margaret M.; Kapteyn, Henry C.

    2015-01-01

    We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform. PMID:26534992

  11. Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism.

    PubMed

    Fan, Tingting; Grychtol, Patrik; Knut, Ronny; Hernández-García, Carlos; Hickstein, Daniel D; Zusin, Dmitriy; Gentry, Christian; Dollar, Franklin J; Mancuso, Christopher A; Hogle, Craig W; Kfir, Ofer; Legut, Dominik; Carva, Karel; Ellis, Jennifer L; Dorney, Kevin M; Chen, Cong; Shpyrko, Oleg G; Fullerton, Eric E; Cohen, Oren; Oppeneer, Peter M; Milošević, Dejan B; Becker, Andreas; Jaroń-Becker, Agnieszka A; Popmintchev, Tenio; Murnane, Margaret M; Kapteyn, Henry C

    2015-11-17

    We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.

  12. Design of plasmonic circular grating with broadband absorption enhancements

    NASA Astrophysics Data System (ADS)

    Chiu, Nan-Fu; Yang, Cheng-Du; Kao, Yi-Lun; Cheng, Chih-Jen

    2015-05-01

    We have investigated the effect of concentric circles geometry on the performance of focusing plasmonic circular grating (PCG)-coupled surface-omnidirectional absorption. We wish to highlight the essential characteristics of plasmonic circular grating nanostructure to assist researchers in developing and advancing suitable organic solar cells (OSC) for unique applications. Exactly how plasmonic enhancement and the absorption characteristics of the organic materials (P3HT:PCBM and PEDOT:PSS) interact with each other is also examined. We present experimental studies of broadband absorption enhancement in PCG structure. We show that the PCG structure can result in broadband absorption enhancement, the overall optical absorption in organic film can be greatly enhanced up to ~111.2 % compared to the planar device without grating.

  13. Characterization of the coral allene oxide synthase active site with UV-visible absorption, magnetic circular dichroism, and electron paramagnetic resonance spectroscopy: evidence for tyrosinate ligation to the ferric enzyme heme iron.

    PubMed

    Abraham, B D; Sono, M; Boutaud, O; Shriner, A; Dawson, J H; Brash, A R; Gaffney, B J

    2001-02-20

    Coral allene oxide synthase (AOS), a hemoprotein with weak sequence homology to catalase, is the N-terminal domain of a naturally occurring fusion protein with an 8R-lipoxygenase. AOS converts 8R-hydroperoxyeicosatetraenoic acid to the corresponding allene oxide. The UV--visible absorption and magnetic circular dichroism spectra of ferric AOS and of its cyanide and azide complexes, and the electron paramagnetic resonance spectra of native AOS (high-spin, g = 6.56, 5.22, 2.00) and of its cyanide adduct (low-spin, g = 2.86, 2.24, 1.60) closely resemble the corresponding spectra of bovine liver catalase (BLC). These results provide strong evidence for tyrosinate ligation to the heme iron of AOS as has been established for catalases. On the other hand, the positive circular dichroism bands in the Soret region for all three derivatives of ferric AOS are almost the mirror image of those in catalase. In addition, the cyanide affinity of native AOS (K(d) = 10 mM at pH 7) is about 3 orders of magnitude lower than that of BLC. Thus, while these results conclusively support a common tyrosinate-ligated heme in AOS as in catalase, significant differences exist in the interaction between their respective heme prosthetic groups and protein environments, and in the access of small molecules to the heme iron. PMID:11329294

  14. Circular magnetic x-ray dichroism in rare earth compounds

    SciTech Connect

    Jonathan, L.

    1993-09-30

    This report discusses the following topics: Circular magnetic x-ray dichroism at the ER L{sub 3} Edge; angular dependence of circular magnetic x-ray dichroism in rare earth compounds: and circular magnetic x-ray dichroism in crystalline and amorphous GDFE{sub 2}.

  15. Photoemission and magnetic circular dichroism studies of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Fujimori, Atsushi

    2005-03-01

    Recently, a series of novel ferromagnetic semiconductors have been synthesized using MBE and related techniques and have attracted much attention because of unknown mechanisms of carrier-induced ferromagnetism and potential applications as "spin electronics" devices. Some new materials show ferromagnetism even well above room temperature. Photoemission spectroscopy has been used to study the d orbitals of the dilute transition-metal atoms, mostly Mn, and their hybridization with the host band states [1]. Soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the transition-metal 2p-3d absorption edges are useful techniques to study the valence and spin states of the transition-metal atoms. Furthermore, since MCD has different sensitivities to the ferromagnetic and paramagnetic components at different temperatures and magnetic fileds, if the sample is a mixture of ferromagnetic and non-ferromagnetic transition- metal atoms, it can be used to separate the two components and to study their electronic structures. In this talk, results are presented for the prototypical diluted ferromagnetic semiconductor Ga1-xMnxAs [2] and the room-temperature ferromagnets Zn1-xCoxO and Ti1-xCoxO2.I acknowledge collaboration with Y. Ishida, J.-I. Hwang, M. Kobayashi, Y. Takeda, Y. Saitoh, J. Okamoto, T. Okane, Y. Muramatsu, K. Mamiya, T. Koide, A. Tanaka, M. Tanaka, Hayashi, S. Ohya, T. Kondo, H. Munekata, H. Saeki, H. Tabata, T. Kawai, Y. Matsumoto, H. Koinuma, T. Fukumura and M. Kawasaki. This work was supported by a Grant-in-Aid for Scientific Research in Priority Area "Semiconductor nano-spintronics" (14076209) from MEXT, Japan.1. J. Okabayashi et al., Phys. Rev. B 64, 125304 (2001).2. A. Fujimori et al., J. Electron Spectrosc. Relat. Phenom., in press.

  16. New applications of x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Schütz, G.; Fischer, P.; Attenkofer, K.; Ahlers, D.

    1997-01-01

    X-ray magnetic circular dichroism (X-MCD) in core-level absorption is intimately related to the local spin and orbital polarization distribution in the final states, as it is based on angular-momentum conservation and the interplay of exchange and spin-orbit interaction. It provides symmetry and element-selective information about magnetic aspects of electronic structure. In favourable cases spin and orbital contributions to the local magnetic moments can be deduced directly by applying the so-called "sum-rules". Recently studies of the dichroic contributions in the EXAFS energy range have attracted considerable attention. From systematic studies in various systems a direct proportionality between the strengths of the magnetic signal and the spin moment has been found. This can be easily explained by an exchange contribution to the Coulomb backscattering amplitude and gives important new insights into the exchange interactions of low-energy electrons in solids. With the advent of new intense x-ray sources a variety of other x-ray methods, which involve core-level absorption, can be used to study magnetism. Recent examples are magnetic anomalous small-angle x-ray scattering and imaging magnetic domains with a zone-plate x-ray microscope, which both provide a high-resolution quantitative details of the spatial magnetization contributions.

  17. Multipole analysis of circular cylindrical magnetic systems

    NASA Astrophysics Data System (ADS)

    Selvaggi, Jerry P.

    This thesis deals with an alternate method for computing the external magnetic field from a circular cylindrical magnetic source. The primary objective is to characterize the magnetic source in terms of its equivalent multipole distribution. This multipole distribution must be valid at points close to the cylindrical source and a spherical multipole expansion is ill-equipped to handle this problem; therefore a new method must be introduced. This method, based upon the free-space Green's function in cylindrical coordinates, is developed as an alternative to the more familiar spherical harmonic expansion. A family of special functions, called the toroidal functions or Q-functions, are found to exhibit the necessary properties for analyzing circular cylindrical geometries. In particular, the toroidal function of zeroth order, which comes from the integral formulation of the free-space Green's function in cylindrical coordinates, is employed to handle magnetic sources which exhibit circular cylindrical symmetry. The toroidal functions, also called Q-functions, are the weighting coefficients in a "Fourier series-like" expansion which represents the free-space Green's function. It is also called a toroidal expansion. This expansion can be directly employed in electrostatic, magnetostatic, and electrodynamic problems which exhibit cylindrical symmetry. Also, it is shown that they can be used as an alternative to the Elliptic integral formulation. In fact, anywhere that an Elliptic integral appears, one can replace it with its corresponding Q-function representation. A number of problems, using the toroidal expansion formulation, are analyzed and compared to existing known methods in order to validate the results. Also, the equivalent multipole distribution is found for most of the solved problems along with its corresponding physical interpretation. The main application is to characterize the external magnetic field due to a six-pole permanent magnet motor in terms of its

  18. Multipole Analysis of Circular Cylindircal Magnetic Systems

    SciTech Connect

    Selvaggi, Jerry P.

    2005-12-01

    This thesis deals with an alternate method for computing the external magnetic field from a circular cylindrical magnetic source. The primary objective is to characterize the magnetic source in terms of its equivalent multipole distribution. This multipole distribution must be valid at points close to the cylindrical source and a spherical multipole expansion is ill-equipped to handle this problem; therefore a new method must be introduced. This method, based upon the free-space Green's function in cylindrical coordinates, is developed as an alternative to the more familiar spherical harmonic expansion. A family of special functions, called the toroidal functions or Q-functions, are found to exhibit the necessary properties for analyzing circular cylindrical geometries. In particular, the toroidal function of zeroth order, which comes from the integral formulation of the free-space Green's function in cylindrical coordinates, is employed to handle magnetic sources which exhibit circular cylindrical symmetry. The toroidal functions, also called Q-functions, are the weighting coefficients in a ''Fourier series-like'' expansion which represents the free-space Green's function. It is also called a toroidal expansion. This expansion can be directly employed in electrostatic, magnetostatic, and electrodynamic problems which exhibit cylindrical symmetry. Also, it is shown that they can be used as an alternative to the Elliptic integral formulation. In fact, anywhere that an Elliptic integral appears, one can replace it with its corresponding Q-function representation. A number of problems, using the toroidal expansion formulation, are analyzed and compared to existing known methods in order to validate the results. Also, the equivalent multipole distribution is found for most of the solved problems along with its corresponding physical interpretation. The main application is to characterize the external magnetic field due to a six-pole permanent magnet motor in terms of

  19. Simulation of magnetic circular dichroism in the electron microscope

    NASA Astrophysics Data System (ADS)

    Rubino, Stefano; Schattschneider, Peter; Rusz, Jan; Verbeeck, Johan; Leifer, Klaus

    2010-12-01

    As electron energy-loss spectroscopy (EELS) and x-ray absorption spectroscopy (XAS) probe the same transitions from core-shell states to unoccupied states above the Fermi energy, it should always be possible to apply the two techniques to the same physical phenomena, such as magnetic dichroism, and obtain the same information. Indeed, the similarity in the expression of the electron and x-ray cross-sections had been already exploited to prove the equivalence of x-ray magnetic linear dichroism and anisotropy in EELS, by noting that the polarization vector of a photon plays the same role as the momentum transfer in electron scattering. Recently, the same was proven true for x-ray magnetic circular dichroism (XMCD) by establishing a new TEM technique called EMCD (electron energy-loss magnetic chiral dichroism) (Schattschneider P et al 2006 Nature 441 486-8), which makes use of special electron scattering conditions to force the absorption of a circularly polarized virtual photon. The intrinsic advantage of EMCD over XMCD is the high spatial resolution of electron microscopes, which are readily available. Among the particular obstacles in EMCD that do not exist for synchrotron radiation, is the notoriously low signal and the very particular scattering conditions necessary to observe a chiral dichroic signal. In spite of that, impressive progress has been made in recent years. The signal strength could be considerably increased, and some innovations such as using a convergent beam have been introduced. EMCD has evolved into several techniques, which make full use of the versatility of the TEM and energy filtering, spectroscopy or STEM conditions (Rubino S 2007 Magnetic circular dichroism in the transmission electron microscope PhD Thesis Vienna University of Technology, Vienna, Austria).

  20. Magnetic circular dichroism of chlorofullerenes: Experimental and computational study

    NASA Astrophysics Data System (ADS)

    Štěpánek, Petr; Straka, Michal; Šebestík, Jaroslav; Bouř, Petr

    2016-03-01

    Magnetic circular dichroism (MCD) spectra of C60Cl6, C70Cl10 and C60Cl24 were measured and interpreted using a sum-over-state (SOS) protocol exploiting time dependent density functional theory (TDDFT). Unlike for plain absorption, the MCD spectra exhibited easily recognizable features specific for each chlorinated molecule and appear as a useful tool for chlorofullerene identification. MCD spectrum of C60Cl24 was below 400 nm partially obscured due to scattering and low solubility. In all cases a finer vibrational structure of the electronic bands was observed at longer wavelengths. The TDDFT simulations provided a reasonable basis for interpretation of the most prominent spectral features.

  1. Magnetic Field Generation through Angular Momentum Exchange between Circularly Polarized Radiation and Charged Particles

    SciTech Connect

    G. Shvets; N.J. Fisch; J.-M. Rax

    2002-01-18

    The interaction between circularly polarized (CP) radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic field generation.

  2. Resonant absorption and amplification of circularly-polarized waves in inhomogeneous chiral media.

    PubMed

    Kim, Seulong; Kim, Kihong

    2016-01-25

    It has been found that in the media where the dielectric permittivity ε or the magnetic permeability μ is near zero and in transition metamaterials where ε or μ changes from positive to negative values, there occur a strong absorption or amplification of the electromagnetic wave energy in the presence of an infinitesimally small damping or gain and a strong enhancement of the electromagnetic fields. We attribute these phenomena to the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations and its inverse process. In this paper, we study analogous phenomena occurring in chiral media theoretically using the invariant imbedding method. In uniform isotropic chiral media, right-circularly-polarized and left-circularly-polarized waves are the eigen-modes of propagation with different effective refractive indices n(+) and n(-), whereas in the chiral media with a nonuniform impedance variation, they are no longer the eigenmodes and are coupled to each other. We find that both in uniform chiral slabs where either n(+) or n(-) is near zero and in chiral transition metamaterials where n(+) or n(-) changes from positive to negative values, a strong absorption or amplification of circularly-polarized waves occurs in the presence of an infinitesimally small damping or gain. We present detailed calculations of the mode conversion coefficient, which measures the fraction of the electromagnetic wave energy absorbed into the medium, for various configurations of ε and μ with an emphasis on the influence of a nonuniform impedance. We propose possible applications of these phenomena to linear and nonlinear optical devices that react selectively to the helicity of the circular polarization. PMID:26832557

  3. Resonant absorption and amplification of circularly-polarized waves in inhomogeneous chiral media.

    PubMed

    Kim, Seulong; Kim, Kihong

    2016-01-25

    It has been found that in the media where the dielectric permittivity ε or the magnetic permeability μ is near zero and in transition metamaterials where ε or μ changes from positive to negative values, there occur a strong absorption or amplification of the electromagnetic wave energy in the presence of an infinitesimally small damping or gain and a strong enhancement of the electromagnetic fields. We attribute these phenomena to the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations and its inverse process. In this paper, we study analogous phenomena occurring in chiral media theoretically using the invariant imbedding method. In uniform isotropic chiral media, right-circularly-polarized and left-circularly-polarized waves are the eigen-modes of propagation with different effective refractive indices n(+) and n(-), whereas in the chiral media with a nonuniform impedance variation, they are no longer the eigenmodes and are coupled to each other. We find that both in uniform chiral slabs where either n(+) or n(-) is near zero and in chiral transition metamaterials where n(+) or n(-) changes from positive to negative values, a strong absorption or amplification of circularly-polarized waves occurs in the presence of an infinitesimally small damping or gain. We present detailed calculations of the mode conversion coefficient, which measures the fraction of the electromagnetic wave energy absorbed into the medium, for various configurations of ε and μ with an emphasis on the influence of a nonuniform impedance. We propose possible applications of these phenomena to linear and nonlinear optical devices that react selectively to the helicity of the circular polarization.

  4. A simple circular-polarized antenna: Circular waveguide horn coated with lossy magnetic material

    NASA Technical Reports Server (NTRS)

    Lee, C. S.; Lee, S. W.; Justice, D. W.

    1986-01-01

    A circular waveguide horn coated with a lossy material in its interior wall can be used as an alternative to a corrugated waveguide for radiating a circularly polarized (CP) field. To achieve good CP radiation, the diameter of the structure must be larger than the free-space wavelength, and the coating material must be sufficiently lossy and magnetic. This device is cheaper and lighter in weight than the corrugated one.

  5. A simple circular-polarized antenna: Circular waveguide horn coated with lossy magnetic material

    NASA Technical Reports Server (NTRS)

    Lee, Choon S.; Justice, D. W.; Lee, Shung-Wu

    1988-01-01

    It is shown that a circular waveguide horn coated with a lossy material in its interior wall can be used as an alternative to a corrugated waveguide for radiating a circularly polarized (CP) field. To achieve good CP radiation, the diameter of the structure must be larger than the free-space wavelength, and the coating material must be sufficiently lossy and magnetic. The device is cheaper and lighter in weight than the corrugated one.

  6. Magnetized Weibel filaments as a source of circularly polarized light

    NASA Astrophysics Data System (ADS)

    Sinha, Ujjwal; Martins, Joana; Vieira, Jorge; Fonseca, Ricardo; Silva, Luis

    2015-11-01

    We investigate radiation spectra of plasma particles trapped in Weibel filaments generated from multidimensional particle in cell simulations with OSIRIS in magnetized and unmagnetized plasmas. We show that an important parameter determining polarization of emitted radiation is the magnetization of ambient media. Polarization of radiation emitted during counter-propagating plasma flows with different magnetizations is explored by extracting trajectories of particles sampled from PIC simulations and computing their radiation spectrum. Particle trajectories in magnetized plasmas undergo EXB drift at Weibel boundaries leading to a preferential drift direction, whereas, in unmagnetized case the particles have no net drift. As a result, significant fraction of radiated energy from magnetized filament is circularly polarized (CP). Energy attributed to different polarizations is calculated by measuring degree of polarizations. With increasing magnetization, the fraction of radiated energy attributed to CP increases. The direction of circular polarization also changes with direction of applied magnetic field. The study is of significance for understanding radiation from Gamma Ray Bursts.

  7. Generation of circularly polarized radiation from a compact plasma-based extreme ultraviolet light source for tabletop X-ray magnetic circular dichroism studies.

    PubMed

    Wilson, Daniel; Rudolf, Denis; Weier, Christian; Adam, Roman; Winkler, Gerrit; Frömter, Robert; Danylyuk, Serhiy; Bergmann, Klaus; Grützmacher, Detlev; Schneider, Claus M; Juschkin, Larissa

    2014-10-01

    Generation of circularly polarized light in the extreme ultraviolet (EUV) spectral region (about 25 eV-250 eV) is highly desirable for applications in spectroscopy and microscopy but very challenging to achieve in a small-scale laboratory. We present a compact apparatus for generation of linearly and circularly polarized EUV radiation from a gas-discharge plasma light source between 50 eV and 70 eV photon energy. In this spectral range, the 3p absorption edges of Fe (54 eV), Co (60 eV), and Ni (67 eV) offer a high magnetic contrast often employed for magneto-optical and electron spectroscopy as well as for magnetic imaging. We simulated and designed an instrument for generation of linearly and circularly polarized EUV radiation and performed polarimetric measurements of the degree of linear and circular polarization. Furthermore, we demonstrate first measurements of the X-ray magnetic circular dichroism at the Co 3p absorption edge with a plasma-based EUV light source. Our approach opens the door for laboratory-based, element-selective spectroscopy of magnetic materials and spectro-microscopy of ferromagnetic domains. PMID:25362374

  8. Generation of circularly polarized radiation from a compact plasma-based extreme ultraviolet light source for tabletop X-ray magnetic circular dichroism studies

    SciTech Connect

    Wilson, Daniel; Rudolf, Denis Juschkin, Larissa; Weier, Christian; Adam, Roman; Schneider, Claus M.; Winkler, Gerrit; Frömter, Robert; Danylyuk, Serhiy; Bergmann, Klaus; Grützmacher, Detlev

    2014-10-15

    Generation of circularly polarized light in the extreme ultraviolet (EUV) spectral region (about 25 eV–250 eV) is highly desirable for applications in spectroscopy and microscopy but very challenging to achieve in a small-scale laboratory. We present a compact apparatus for generation of linearly and circularly polarized EUV radiation from a gas-discharge plasma light source between 50 eV and 70 eV photon energy. In this spectral range, the 3p absorption edges of Fe (54 eV), Co (60 eV), and Ni (67 eV) offer a high magnetic contrast often employed for magneto-optical and electron spectroscopy as well as for magnetic imaging. We simulated and designed an instrument for generation of linearly and circularly polarized EUV radiation and performed polarimetric measurements of the degree of linear and circular polarization. Furthermore, we demonstrate first measurements of the X-ray magnetic circular dichroism at the Co 3p absorption edge with a plasma-based EUV light source. Our approach opens the door for laboratory-based, element-selective spectroscopy of magnetic materials and spectro-microscopy of ferromagnetic domains.

  9. Magnetic circular dichroism in the hard X-ray range

    NASA Astrophysics Data System (ADS)

    Rogalev, A.; Wilhelm, F.

    2015-12-01

    An overview of X-ray magnetic circular dichroism (XMCD) spectroscopy in the hard X-ray range is presented. A short historical overview shows how this technique has evolved from the early days of X-ray physics to become a workhorse technique in the modern magnetism research As with all X-ray spectroscopies, XMCD has the advantage of being element specific. Interpretation of the spectra based on magneto-optical sum rules can provide unique information about spin and orbital moment carried by absorbing atom in both amplitude and direction, can infer magnetic interactions from element selective magnetization curves, can allow separation of magnetic and non-magnetic components in heterogeneous systems. The review details the technology currently available for XMCD measurements in the hard X-ray range referring to the ESRF beamline ID12 as an example. The strengths of hard X-ray magnetic circular dichroism technique are illustrated with a wide variety of representative examples, such as actinide based ferromagnets, paramagnetism in metals, pure metallic nanoparticles, exchange spring magnets, half metallic ferromagnets, magnetism at interfaces, and dilute magnetic semiconductors. In this way, we aim to encourage researchers from various scientific communities to consider XMCD as a tool to understanding the electronic and magnetic properties of their samples.

  10. All-optical switching in granular ferromagnets caused by magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Ellis, Matthew O. A.; Fullerton, Eric E.; Chantrell, Roy W.

    2016-07-01

    Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength.

  11. All-optical switching in granular ferromagnets caused by magnetic circular dichroism.

    PubMed

    Ellis, Matthew O A; Fullerton, Eric E; Chantrell, Roy W

    2016-01-01

    Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength. PMID:27466066

  12. All-optical switching in granular ferromagnets caused by magnetic circular dichroism

    PubMed Central

    Ellis, Matthew O. A.; Fullerton, Eric E.; Chantrell, Roy W.

    2016-01-01

    Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength. PMID:27466066

  13. Remediation of Cr(VI) by biogenic magnetic nanoparticles: An x-ray magnetic circular dichroism study

    SciTech Connect

    Telling, N. D.; Coker, V. S.; Cutting, R. S.; van der Laan, G.; Pearce, C. I.; Pattrick, R. A. D.; Arenholz, E.; Lloyd, J. R.

    2009-09-04

    Biologically synthesized magnetite (Fe{sub 3}O{sub 4}) nanoparticles are studied using x-ray absorption and x-ray magnetic circular dichroism following exposure to hexavalent Cr solution. By examining their magnetic state, Cr cations are shown to exist in trivalent form on octahedral sites within the magnetite spinel surface. The possibility of reducing toxic Cr(VI) into a stable, non-toxic form, such as a Cr{sup 3+}-spinel layer, makes biogenic magnetite nanoparticles an attractive candidate for Cr remediation.

  14. Relationship between the magnetic moment of Lu and the magnetic behavior of (Y{sub y}Lu{sub 1-y})(Co{sub 1-x}Al{sub x}){sub 2} from x-ray absorption spectroscopy and x-ray magnetic circular dichroism

    SciTech Connect

    Chaboy, J.; Piquer, C.; Laguna-Marco, M. A.; Kawamura, N.; Suzuki, M.; Takagaki, M.

    2007-02-01

    We present an x-ray magnetic circular dichroism (XMCD) study performed at both the Co K edge and the Lu L{sub 2,3} edges on (Y{sub y}Lu{sub 1-y})(Co{sub 1-x}Al{sub x}){sub 2} systems. The XMCD spectra reflect the different magnetic character of these systems, allowing us to monitor the transition from weak to strong ferromagnetism. The XMCD at the Lu L{sub 2,3} edges indicates the existence of an ordered 5d moment at the lutetium sites that is coupled antiparallel to the Co moment. Estimates of the magnetic moment of Lu have been obtained by applying the XMCD sum rules. Our results show that there is a correlation between the Lu 5d-induced magnetic moment and the magnetic character of the (Y{sub y}Lu{sub 1-y})(Co{sub 1-x}Al{sub x}){sub 2} compounds. These results suggest that the developing of the Lu moment plays an important role in reinforcing the magnetic interactions and favoring the ferromagnetic character of the Lu-rich compounds.

  15. Interpretation of the absorption and circular dichroic spectra of oriented purple membrane films.

    PubMed Central

    Muccio, D D; Cassim, J Y

    1979-01-01

    The absorption and circular dichroic (CD) spectra of purple membrane films in which the plane of the membranes is oriented perpendicular to the incident beam are compared with the solution spectra. This enables one to relate structural features of the purple membrane to a coordinate system as defined by a normal to the membrane plane and two mutually perpendicular in-plane axes. The film and solution absorption spectra were similar except for a relative depression in the 200 - 225-nm region of the film spectrum. However, the CD spectra showed significant differences in the visible region, where the biphasic band in the solution spectrum was replaced by a single positive band at 555 nm in the film spectrum and in the far ultraviolet region, where the 208-nm band was deleted from the film spectra of the native and regenerated membranes. Moreover, a small shoulder occurred at 208 nm in the film spectrum of the bleached membrane. The near ultraviolet spectra also showed differences, whereas the 317-nm band remained essentially the same for both spectra. Based on excitonic interpretations of the visible and far ultraviolet spectra the following conclusions were reached: (a) a relatively strong in-plane monomeric interaction occurs between te retinyl chromophore and apoprotein; (b) the helical axes of the native and regenerated membrane proteins are oriented primarily normal to the membrane plane; and (c) the helical axes of the bleached membrane proteins are tilted more in-plane than the axes of the native or regenerated membrane. Additional conclusions were that an interaction occurs between an in-plane magnetic dipole moment of the retinyl chromophore and probably an in-plane electric dipole moment of a nearby aromatic amino acid(s), and that although the membrane is anisotropic with respect to coupling between electric and magnetic moments of the aromatic amino acids, the transition dipole moments of the aromatic amino acids are not preferentially oriented in either

  16. Time-Resolved X-Ray Magnetic Circular Dichroism - A Selective Probe of Magnetization Dynamics on Nanosecond Timescales

    NASA Astrophysics Data System (ADS)

    Pizzini, Stefania; Vogel, Jan; Bonfim, Marlio; Fontaine, Alain

    Many synchrotron radiation techniques have been developed in the last 15 years for studying the magnetic properties of thin-film materials. The most attractive properties of synchrotron radiation are its energy tunability and its time structure. The first property allows measurements in resonant conditions at an absorption edge of each of the magnetic elements constituting the probed sample, and the latter allows time-resolved measurements on subnanosecond timescales. In this review, we introduce some of the synchrotron-based techniques used for magnetic investigations. We then describe in detail X-ray magnetic circular dichroism (XMCD) and how time-resolved XMCD studies can be carried out in the pump-probe mode. Finally, we illustrate some applications to magnetization reversal dynamics in spin valves and tunnel junctions, using fast magnetic field pulses applied along the easy magnetization axis of the samples. Thanks to the element-selectivity of X-ray absorption spectroscopy, the magnetization dynamics of the soft (Permalloy) and the hard (cobalt) layers can be studied independently. In the case of spin valves, this allowed us to show that two magnetic layers that are strongly coupled in a static regime can become uncoupled on nanosecond timescales.Present address: Universidade Federal do Paraná, Centro Politécnico CP 19011, Curitiba - PR CEP 81531-990, Brazil

  17. Quantum theory of spin alignment in a circular magnetic nanotube

    NASA Astrophysics Data System (ADS)

    Bergmann, Gerd; Thompson, Richard S.; Lu, Jia G.

    2015-12-01

    When electron spin and momentum couple in a solid, one generally obtains intriguing and unexpected phenomena. Metallic ferromagnetic nanotubes of cobalt with circular magnetization, which have been prepared by us and others, are a particularly interesting system. Here the spins of the conduction electrons are frustrated. They would like to align parallel to the magnetic field of the magnetization, but as the electrons move quickly around the tube the spins cannot follow the magnetization direction. In a previous short theoretical paper we solved the spin dynamics using a classical model. Here we generalize our work to a quantum mechanical model. The surprising result is that the spin of most conduction electrons is not parallel or anti-parallel to the circumferential magnetization but mostly parallel or anti-parallel to the axis of the nanotube. This result means that such a cobalt nanotube is a different ferromagnet from a cobalt film or bulk cobalt.

  18. Edge absorption and circular photogalvanic effect in 2D topological insulator edges

    NASA Astrophysics Data System (ADS)

    Entin, M. V.; Magarill, L. I.

    2016-06-01

    The electron absorption on the edge states and the edge photocurrent of a 2D topological insulator (TI) are studied. We consider the optical transitions within linear edge branches of the energy spectrum. The interaction with impurities is taken into account. The circular polarization is found to produce the edge photocurrent, the direction of which is determined by light polarization and edge orientation.

  19. Magnetic dichroism effect of binary alloys using circularly-polarized x-ray

    SciTech Connect

    Wu, S. Z.; Schumann, F.O.; Willis, R.F.; Goodman, K.W.; Tobin, J.G.; Carr, R.

    1997-05-01

    We have studies the magnetic propertied of CoNi binary alloy films with various atomic compositions using soft x-ray magnetic circular dichroism (XMCD) technique. The alloy films were deposited on single Cu(100) crystals in situ using our well-established epitaxial growth technique to achieve a layer-by-layer growth and a metastable fcc structure, with all films exhibiting an in-plane magnetic anistrophy. Utilizing the element-specific ability and nanostructure magnetization sensitivity of this technique, we have been able to perform the absorption measurements at L2 and L3 edge of Co and Ni atoms and observed large dichroism signals. The extraction of spin moment and orbital moment for varying elemental stoichiometry using magneto- optical sum rules is discussed.

  20. Diagnostic of stellar magnetic fields with cumulative circular polarisation profiles

    NASA Astrophysics Data System (ADS)

    Kochukhov, O.

    2015-08-01

    Information about stellar magnetic field topologies is obtained primarily from high-resolution circular polarisation (Stokes V) observations. Because of their generally complex morphologies, the stellar Stokes V profiles are usually interpreted with elaborate inversion techniques such as Zeeman Doppler imaging (ZDI). Here we further develop a new method for interpreting circular polarisation signatures in spectral lines using cumulative Stokes V profiles (anti-derivative of Stokes V). This method is complimentary to ZDI and can be applied to validate the inversion results or when the available observational data are insufficient for an inversion. Based on the rigorous treatment of polarised line formation in the weak-field regime, we show that, for rapidly rotating stars, the cumulative Stokes V profiles contain information about the spatially resolved longitudinal magnetic field density. Rotational modulation of these profiles can be employed for a simple, qualitative characterisation of the stellar magnetic field topologies. We apply this diagnostic method to the archival observations of the weak-line T Tauri star V410 Tau and Bp He-strong star HD 37776. We show that the magnetic field in V410 Tau is dominated by an azimuthal component, in agreement with the ZDI map that we recover from the same data set. For HD 37776 the cumulative Stokes V profile variation indicates the presence of multiple regions of positive and negative field polarity. This behaviour agrees with the ZDI results, but contradicts the popular hypothesis that the magnetic field of this star is dominated by an axisymmetric quadrupolar component.

  1. Electrostatic instabilities in circularly polarized microwave produced magnetized plasmas

    SciTech Connect

    Ghorbanalilu, M.; Shokri, B.

    2009-12-15

    The growth rate of electrostatic instabilities of electron oscillation and low-frequency (LF) ion oscillation are investigated for a plasma produced by a circularly polarized microwave field during the breakdown process. The plasma is magnetized by an external homogenous static magnetic field on the direction of microwave field propagation. Numerical calculations show that the electron and ion perturbations are unstable in such an anisotropic plasma. Electron perturbations have the maximum growth rate across the magnetic field. In addition, ion perturbation growth rate is minimum on this direction. The LF ion oscillation is excited by Cherenkov emission mechanism due to the nonequilibrium form of the electron velocity distribution function. Electron oscillation growth rate decreases by increasing the external magnetic field, while the LF ion oscillation increases smoothly and reaches a maximum when the electron oscillation is stopped.

  2. Magnetic x-ray circular dichroism in Fe Co Pt multilayers

    SciTech Connect

    Tobin, J.G.; Jankowski, A.F.; Waddill, G.D.; Sterne, P.A.

    1994-04-01

    Magnetic x-ray circular dichroism in x-ray absorption has been used to investigate the ternary multilayer system, Fe Co Pt. Samples were prepared by planar magnetron sputter deposition and carefully characterized, using a variety of techniques such as grazing-incidence and high-angle x-ray scattering, Auger depth profiling and cross-section transmission electron microscopy. As previously reported, the Fe9.5{Angstrom} Pt9.5{Angstrom} exhibits a large dichroism in the Fe 2p absorption. Interestingly while the Co9.5{Angstrom} Pt9.5{Angstrom} has no measurable dichroism, the Fe4.7{Angstrom} Co4.7{Angstrom} Pt9.5{Angstrom} sample has a dichroism at both the Fe 2p and Co 2p absorption edges. These and other results are compared to slab calculation predictions. Possible explanations are discussed.

  3. Probing arrays of circular magnetic microdots by ferromagnetic resonance.

    SciTech Connect

    Kakazei, G. N.; Mewes, T.; Wigen, P. E.; Hammel, P. C.; Slavin, A. N.; Pogorelov, Y. G.; Costa, M. D.; Golub, V. O.; Guslienko, K. Y.; Novosad, V.

    2008-06-01

    X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions.

  4. [Microwave absorption by magnetic nanoparticles in organisms].

    PubMed

    Bingi, V N

    2011-01-01

    An estimate of the rate of absorption of the electromagnetic microwaves by magnetic nanoparticles in organisms is presented. The absorption takes place due to the energy dissipation at the ferromagnetic resonance. Based on the known solution of the Landau-Lifshitz equation, the imaginary part of the complex magnetic susceptibility is evaluated that gives the absorption rate. It is shown that even in the conditions of thermal isolation of the particles, their temperature growth would be insignificant at absorption of the emission with the energy flux density of the order of 1 mW/cm2, and the given mechanism is unrelated to the observable effects of low-intensity microwaves. PMID:22279759

  5. Impulse absorption by horizontal magnetic granular chain

    NASA Astrophysics Data System (ADS)

    Leng, Dingxin; Wang, Xiaojie; Liu, Guijie; Sun, Lingyu

    2016-02-01

    The granular medium is known as a protecting material for shock mitigation. We study the impulse absorption of an alignment of magnetic spheres placed horizontally under a non-uniform magnetic field. The phenomenon of the wave dispersion is presented. This system can absorb 85% ˜ 95% (88% ˜ 98%) of the incident peak force (energy) under the applied magnetic field strength in 0.1 T ˜ 1.0 T. The shock attenuation capacities are enhanced by the increment of field strength. With an intelligent control system, it is conceivable that the magnetic granular chain may offer possibilities in developing adaptive shock protectors.

  6. Instrument for x-ray magnetic circular dichroism measurements at high pressures

    SciTech Connect

    Haskel, D.; Tseng, Y. C.; Lang, J. C.; Sinogeikin, S.

    2007-08-15

    An instrument has been developed for x-ray magnetic circular dichroism (XMCD) measurements at high pressures and low temperatures. This instrument couples a nonmagnetic copper-beryllium diamond anvil cell featuring perforated diamonds with a helium flow cryostat and an electromagnet. The applied pressure can be controlled in situ using a gas membrane and calibrated using Cu K-edge x-ray absorption fine structure measurements. The performance of this instrument was tested by measuring the XMCD spectra of the Gd{sub 5}Si{sub 2}Ge{sub 2} giant magnetocaloric material.

  7. Circular polarization in a non-magnetic resonant tunneling device.

    PubMed

    Dos Santos, Lara F; Gobato, Yara Galvão; Teodoro, Márcio D; Lopez-Richard, Victor; Marques, Gilmar E; Brasil, Maria Jsp; Orlita, Milan; Kunc, Jan; Maude, Duncan K; Henini, Mohamed; Airey, Robert J

    2011-01-01

    We have investigated the polarization-resolved photoluminescence (PL) in an asymmetric n-type GaAs/AlAs/GaAlAs resonant tunneling diode under magnetic field parallel to the tunnel current. The quantum well (QW) PL presents strong circular polarization (values up to -70% at 19 T). The optical emission from GaAs contact layers shows evidence of highly spin-polarized two-dimensional electron and hole gases which affects the spin polarization of carriers in the QW. However, the circular polarization degree in the QW also depends on various other parameters, including the g-factors of the different layers, the density of carriers along the structure, and the Zeeman and Rashba effects. PMID:21711613

  8. Multi circular-cavity surface coil for magnetic resonance imaging of monkey's brain at 4 Tesla

    NASA Astrophysics Data System (ADS)

    Osorio, A. I.; Solis-Najera, S. E.; Vázquez, F.; Wang, R. L.; Tomasi, D.; Rodriguez, A. O.

    2014-11-01

    Animal models in medical research has been used to study humans diseases for several decades. The use of different imaging techniques together with different animal models offers a great advantage due to the possibility to study some human pathologies without the necessity of chirurgical intervention. The employ of magnetic resonance imaging for the acquisition of anatomical and functional images is an excellent tool because its noninvasive nature. Dedicated coils to perform magnetic resonance imaging experiments are obligatory due to the improvement on the signal-to-noise ratio and reduced specific absorption ratio. A specifically designed surface coil for magnetic resonance imaging of monkey's brain is proposed based on the multi circular-slot coil. Numerical simulations of the magnetic and electric fields were also performed using the Finite Integration Method to solve Maxwell's equations for this particular coil design and, to study the behavior of various vector magnetic field configurations and specific absorption ratio. Monkey's brain images were then acquired with a research-dedicated magnetic resonance imaging system at 4T, to evaluate the anatomical images with conventional imaging sequences. This coil showed good quality images of a monkey's brain and full compatibility with standard pulse sequences implemented in research-dedicated imager.

  9. All-optical magnetization reversal by circularly polarized laser pulses: Experiment and multiscale modeling

    NASA Astrophysics Data System (ADS)

    Vahaplar, K.; Kalashnikova, A. M.; Kimel, A. V.; Gerlach, S.; Hinzke, D.; Nowak, U.; Chantrell, R.; Tsukamoto, A.; Itoh, A.; Kirilyuk, A.; Rasing, Th.

    2012-03-01

    We present results of detailed experimental and theoretical studies of all-optical magnetization reversal by single circularly-polarized laser pulses in ferrimagnetic rare earth—transition metal (RE-TM) alloys GdxFe90-xCo10 (20%magnetization during the reversal process. This reversal does not involve precessional motion of magnetization but is governed by the longitudinal relaxation and thus has a linear character. We demonstrate that this all-optically driven linear reversal can be modeled as a result of a two-fold impact of the laser pulse on the medium. First, due to absorption of the light and ultrafast laser-induced heating, the medium is brought to a highly nonequilibrium state. Simultaneously, due to the ultrafast inverse Faraday effect the circularly polarized laser pulse acts as an effective magnetic field of the amplitude up to ˜20 T. We show that the polarization-dependent reversal triggered by the circularly polarized light is feasible only in a narrow range (below 10%) of laser fluences. The duration of the laser pulse required for the reversal can be varied from ˜40 fs up to at least ˜1700 fs. We also investigate experimentally the role of the ferrimagnetic properties of GdFeCo in the all-optical reversal. In particular, the optimal conditions for the all-optical reversal are achieved just below the ferrimagnetic compensation temperature, where the magnetic information can be all-optically written by a laser pulse of minimal fluence and read out within just 30 ps. We argue that this is the fastest write-read event demonstrated for magnetic recording so far.

  10. Time-resolved circular dichroism and absorption studies of the photolysis reaction of (carbonmonoxy)myoglobin.

    PubMed Central

    Milder, S J; Bjorling, S C; Kuntz, I D; Kliger, D S

    1988-01-01

    Time-resolved circular dichroism (TRCD) and absorption spectroscopy are used to follow the photolysis reaction of (carbonmonoxy)myoglobin (MbCO). Following the spectral changes associated with the initial loss of CO, a subtle change is observed in the visible absorption spectrum of the Mb product on a time scale of a few hundred nanoseconds. No changes are seen in the CD spectrum of Mb in the visible and near-UV regions subsequent to the loss of CO. The data suggest the existence of an intermediate found after ligand loss from MbCO that is similar in structure to the final Mb product. PMID:3390516

  11. Magnetic instability in a dilute circular rarefaction wave

    SciTech Connect

    Dieckmann, M. E.; Sarri, G.; Borghesi, M.

    2012-12-15

    The growth of magnetic fields in the density gradient of a rarefaction wave has been observed in simulations and in laboratory experiments. The thermal anisotropy of the electrons, which gives rise to the magnetic instability, is maintained by the ambipolar electric field. This simple mechanism could be important for the magnetic field amplification in astrophysical jets or in the interstellar medium ahead of supernova remnant shocks. The acceleration of protons and the generation of a magnetic field by the rarefaction wave, which is fed by an expanding circular plasma cloud, is examined here in form of a 2D particle-in-cell simulation. The core of the plasma cloud is modeled by immobile charges, and the mobile protons form a small ring close to the cloud's surface. The number density of mobile protons is thus less than that of the electrons. The protons of the rarefaction wave are accelerated to 1/10 of the electron thermal speed, and the acceleration results in a thermal anisotropy of the electron distribution in the entire plasma cloud. The instability in the rarefaction wave is outrun by a TM wave, which grows in the dense core distribution, and its magnetic field expands into the rarefaction wave. This expansion drives a secondary TE wave.

  12. First-principles analysis of X-ray magnetic circular dichroism for transition metal complex oxides

    NASA Astrophysics Data System (ADS)

    Ikeno, Hidekazu

    2016-10-01

    X-ray magnetic circular dichroism (XMCD) is widely used for the characterization of magnetism of materials. However, information from XMCD related to the atomic, electronic, and magnetic structures is not fully utilized due to the lack of reliable theoretical tools for spectral analysis. In this work, the first-principles configuration interaction (CI) calculations for X-ray absorption spectra developed by the author were extended for the calculation of XMCD, where the Zeeman energy was taken into the Hamiltonian of the CI to mimic magnetic polarization in the solid state. This technique was applied to interpret the L2,3 XMCD from 3d transition metal complex oxides, such as NiFe2O4 and FeTiO3. The experimental XMCD spectra were quantitatively reproduced using this method. The oxidation states as well as the magnetic ordering between transition metal ions on crystallographically different sites in NiFe2O4 can be unambiguously determined. A first-principles analysis of XMCD in FeTiO3 revealed the presence of Fe3+ and Ti3+ ions, which indicates that the charge transfer from Fe to Ti ions occurs. The origin of magnetic polarization of Ti ions in FeTiO3 was also discussed.

  13. Large-amplitude circularly polarized electromagnetic waves in magnetized plasma

    SciTech Connect

    Vasko, I. Y. Artemyev, A. V.; Zelenyi, L. M.

    2014-05-15

    We consider large-amplitude circularly polarized (LACP) waves propagating in a magnetized plasma. It is well-known that the dispersion relation for such waves coincides with the dispersion relation given by the linear theory. We develop the model of LACP wave containing a finite population of Cerenkov resonant particles. We find that the current of resonant particles modifies the linear dispersion relation. Dispersion curves of low-frequency (i.e., whistler and magnetosonic) waves are shifted toward larger values of the wave vector, i.e., waves with arbitrarily large wavelengths do not exist in this case. Dispersion curves of high-frequency waves are modified so that the wave phase velocity becomes smaller than the speed of light.

  14. Tunable Circularly Polarized Terahertz Radiation from Magnetized Gas Plasma.

    PubMed

    Wang, W-M; Gibbon, P; Sheng, Z-M; Li, Y-T

    2015-06-26

    It is shown, by simulation and theory, that circularly or elliptically polarized terahertz radiation can be generated when a static magnetic (B) field is imposed on a gas target along the propagation direction of a two-color laser driver. The radiation frequency is determined by √[ω(p)(2)+ω(c)(2)/4]+ω(c)/2, where ω(p) is the plasma frequency and ω(c) is the electron cyclotron frequency. With the increase of the B field, the radiation changes from a single-cycle broadband waveform to a continuous narrow-band emission. In high-B-field cases, the radiation strength is proportional to ω(p)(2)/ω(c). The B field provides a tunability in the radiation frequency, spectrum width, and field strength.

  15. Scaling of the L{sub 2,3} circular magnetic x-ray dichroism of Fe nitrides

    SciTech Connect

    Alouani, M. |; Wills, J.M.; Wilkins, J.W.

    1998-04-01

    We have implemented the calculation of the x-ray-absorption cross section for left- and right-circularly polarized x-ray beams within the local-density approximation by means of our all-electron full-relativistic and spin-polarized full-potential linear muffin-tin orbital method. We show that the L{sub 2,3} circular magnetic x-ray dichroism of Fe, Fe{sub 3}N, and Fe{sub 4}N compounds scales to a single curve when divided by the local magnetic moment. Sum rules determine the spin and orbital magnetic moment of iron atoms in these ordered iron nitrides. {copyright} {ital 1998} {ital The American Physical Society}

  16. Time Resolved X-ray Magnetic Circular Dichroism at the Linac Coherent Light Source

    NASA Astrophysics Data System (ADS)

    Schlotter, W.; Higley, D.; Jal, E.; Dakovski, G.; Yuan, E.; MacArthur, J.; Lutman, A.; Hirsch, K.; Granitzka, P.; Chen, Z.; Coslovich, G.; Hoffman, M.; Mitra, A.; Reid, A.; Hart, P.; Nuhn, H.-D.; Duerr, H.; Arenholz, E.; Shafer, P.; Dennes, P.; Joseph, J.; Guyader, L.; Tsukamoto, A.

    We demonstrate ultrafast time resolved X-ray Magnetic Circular Dichroism on optically switchable GdFeCo thin film samples. This method extends the element specificity of time resolved x-ray absorption spectroscopy to characterize the evolution of electron spin and orbital angular momenta. These measurements were enabled by a recent upgrade at the Linac Coherent Light Source (LCLS) to generate circularly polarized x-rays. Additionally these measurements were enhanced by new detection systems that benefit all x-ray absorption spectroscopy experiments performed in transmission. Consequently static XMCD data are in excellent agreement with similar measurements at synchrotron light sources. The LCLS is an x-ray free electron laser user facility accessible via a peer-reviewed proposal process. Acknowledgement: The Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.

  17. Giant Two-photon Absorption in Circular Graphene Quantum Dots in Infrared Region.

    PubMed

    Feng, Xiaobo; Li, Zhisong; Li, Xin; Liu, Yingkai

    2016-01-01

    We investigate theoretically the two-photon absorption (TPA) for circular graphene quantum dots (GQDs) with the edge of armchair and zigzag on the basis of electronic energy states obtained by solving the Dirac-Weyl equation numerically under finite difference method. The expressions for TPA cross section are derived and the transition selection rules are obtained. Results reveal that the TPA is significantly greater in GQDs than conventional semiconductor QDs in infrared spectrum (2-6 um) with a resonant TPA cross section of up to 10(11 )GM. The TPA peaks are tuned by the GQDs' size, edge and electron relaxation rate.

  18. Theoretical electronic absorption and natural circular dichroism spectra of (-)-trans-cyclooctene

    NASA Astrophysics Data System (ADS)

    Pedersen, Thomas Bondo; Koch, Henrik

    2000-02-01

    Using the random phase approximation and coupled cluster singles and doubles linear response theory in conjunction with two basis sets of augmented double-zeta quality and two nuclear geometries, we have calculated electronic absorption and natural circular dichroism spectra of (-)-trans-cyclooctene. We present a density functional theory optimized nuclear geometry whose ground state electric dipole moment and harmonic vibrational spectrum compare well with experimental data. The coupled cluster results obtained with this nuclear geometry are in good agreement with experimental electronic spectra, although the original interpretation of the most intense low-lying band as a π→π* transition is contradicted.

  19. Size-dependent two-photon absorption in circular graphene quantum dots.

    PubMed

    Feng, Xiaobo; Li, Xin; Li, Zhisong; Liu, Yingkai

    2016-02-01

    We investigate theoretically the size-dependence of two-photon absorption (TPA) for circular graphene quantum dots (GQDs) on the basis of electronic energy states obtained by solving the Dirac-Weyl equation analytically under infinite-mass boundary condition. The analytical expressions for TPA coefficient are derived with an arbitrary size-distribution and the transition selection rules are obtained. Results reveal that the intraband transitions in conduction band and valence band contribute much more to TPA than interband transitions. The energy spectrum and TPA peaks are tuned by the size of GQDs. PMID:26906856

  20. Giant Two-photon Absorption in Circular Graphene Quantum Dots in Infrared Region

    NASA Astrophysics Data System (ADS)

    Feng, Xiaobo; Li, Zhisong; Li, Xin; Liu, Yingkai

    2016-09-01

    We investigate theoretically the two-photon absorption (TPA) for circular graphene quantum dots (GQDs) with the edge of armchair and zigzag on the basis of electronic energy states obtained by solving the Dirac-Weyl equation numerically under finite difference method. The expressions for TPA cross section are derived and the transition selection rules are obtained. Results reveal that the TPA is significantly greater in GQDs than conventional semiconductor QDs in infrared spectrum (2-6 um) with a resonant TPA cross section of up to 1011 GM. The TPA peaks are tuned by the GQDs’ size, edge and electron relaxation rate.

  1. Giant Two-photon Absorption in Circular Graphene Quantum Dots in Infrared Region.

    PubMed

    Feng, Xiaobo; Li, Zhisong; Li, Xin; Liu, Yingkai

    2016-01-01

    We investigate theoretically the two-photon absorption (TPA) for circular graphene quantum dots (GQDs) with the edge of armchair and zigzag on the basis of electronic energy states obtained by solving the Dirac-Weyl equation numerically under finite difference method. The expressions for TPA cross section are derived and the transition selection rules are obtained. Results reveal that the TPA is significantly greater in GQDs than conventional semiconductor QDs in infrared spectrum (2-6 um) with a resonant TPA cross section of up to 10(11 )GM. The TPA peaks are tuned by the GQDs' size, edge and electron relaxation rate. PMID:27629800

  2. Giant Two-photon Absorption in Circular Graphene Quantum Dots in Infrared Region

    PubMed Central

    Feng, Xiaobo; Li, Zhisong; Li, Xin; Liu, Yingkai

    2016-01-01

    We investigate theoretically the two-photon absorption (TPA) for circular graphene quantum dots (GQDs) with the edge of armchair and zigzag on the basis of electronic energy states obtained by solving the Dirac-Weyl equation numerically under finite difference method. The expressions for TPA cross section are derived and the transition selection rules are obtained. Results reveal that the TPA is significantly greater in GQDs than conventional semiconductor QDs in infrared spectrum (2–6 um) with a resonant TPA cross section of up to 1011 GM. The TPA peaks are tuned by the GQDs’ size, edge and electron relaxation rate. PMID:27629800

  3. Magnetic particle hyperthermia: Néel relaxation in magnetic nanoparticles under circularly polarized field.

    PubMed

    de Châtel, P F; Nándori, I; Hakl, J; Mészáros, S; Vad, K

    2009-03-25

    The mechanism of magnetization reversal in single-domain ferromagnetic particles is of interest in many applications, in most of which losses must be minimized. In cancer therapy by hyperthermia the opposite requirement prevails: the specific loss power should be maximized. Of the mechanisms of dissipation, here we study the effect of Néel relaxation on magnetic nanoparticles unable to move or rotate and compare the losses in linearly and circularly polarized fields. We present exact analytical solutions of the Landau-Lifshitz equation as derived from the Gilbert equation and use the calculated time-dependent magnetizations to find the energy loss per cycle. In frequencies lower than the Larmor frequency, linear polarization is found to be the better source of heat power, at high frequencies (beyond the Larmor frequency) circular polarization is preferable.

  4. Magnetic circular dichroism spectroscopy on the Cr₈ antiferromagnetic ring.

    PubMed

    van Slageren, Joris; Piligkos, Stergios; Neese, Frank

    2010-05-28

    A Magnetic Circular Dichroism (MCD) spectroscopic study of the antiferromagnetic ring [Cr₈F₈Piv₁₆] (Piv = pivalate) is reported. From the splitting of the MCD bands, the single ion anisotropy parameters in the cluster spin ground state at different fields were determined to be d(Cr) = -0.33 ± 0.02 cm⁻¹, e(Cr) = 0.11 ± 0.01 cm⁻¹. Analysis of the MCD intensity as a function of field and temperature revealed the influence of spin mixing effects and yielded independent estimates of the single ion anisotropies (d(Cr) = -0.19 cm⁻¹, e(Cr) = 4.3 × 10-4 cm⁻¹), as well as yielding the isotropic exchange interaction strength (J = -6.00 cm⁻¹). Thus it is shown that MCD is a powerful method to unravel the relation between single-ion and cluster anisotropy, furthering the design of molecular magnets with desired properties.

  5. Facility for combined in situ magnetron sputtering and soft x-ray magnetic circular dichroism

    SciTech Connect

    Telling, N. D.; Laan, G. van der; Georgieva, M. T.; Farley, N. R. S.

    2006-07-15

    An ultrahigh vacuum chamber that enables the in situ growth of thin films and multilayers by magnetron sputtering techniques is described. Following film preparation, x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements are performed by utilizing an in vacuum electromagnet. XMCD measurements on sputtered thin films of Fe and Co yield spin and orbital moments that are consistent with those obtained previously on films measured in transmission geometry and grown in situ by evaporation methods. Thin films of FeN prepared by reactive sputtering are also examined and reveal an apparent enhancement in the orbital moment for low N content samples. The advantages of producing samples for in situ XAS and XMCD studies by magnetron sputtering are discussed.

  6. Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip

    PubMed Central

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin; Kersell, Heath; Chang, Hao; Rosenmann, Daniel; Miller, Dean; Freeland, John W.; Hla, Saw-Wai; Rose, Volker

    2016-01-01

    Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L 2,3-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain. PMID:26917146

  7. Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip

    DOE PAGES

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin; Kersell, Heath; Chang, Hao; Rosenmann, Daniel; Miller, Dean; Freeland, John W.; Hla, Saw -Wai; Rose, Volker

    2016-01-28

    Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the FeL2,3-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

  8. Irradiation induced ferromagnetism at room temperature in TiO{sub 2} thin films: X-ray magnetic circular dichroism characterizations

    SciTech Connect

    Thakur, Hardeep; Sharma, K. K.; Thakur, P.; Brookes, N. B.; Kumar, Ravi; Singh, A. P.; Kumar, Yogesh; Gautam, S.; Chae, K. H.

    2011-05-09

    We report on the room temperature ferromagnetism in the swift heavy ion (SHI) irradiated TiO{sub 2} thin films by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) experiments at the O K and Ti L{sub 3,2} absorption edges. The XAS/XMCD measurements provide direct evidence of magnetic polarization of the O 2p and Ti 3d orbitals. The unquenched orbital magnetic moment within the O 2p shell is ferromagnetically coupled to the neighboring Ti moments, which illustrates the intense hybridization of the O 2p and Ti 3d orbitals induced by SHI irradiation.

  9. Experimental test of absorption flattening correction for circular dichroism of particle suspensions.

    PubMed

    Gerdova, Anna; Kelly, Sharon M; Halling, Peter

    2011-08-01

    There are well established theoretical models for correction for absorption flattening of circular dichroism (CD) measurements on particle suspensions. However, these have not been directly tested experimentally. We describe a test system with the chiral tris(ethylenediamine)Co(III) complex dissolved in water trapped inside sephadex particles, suspended in 1-butanol. Independent measurements of particle size distribution, volume fraction, and the absorbance of the suspension are used to calculate the required CD correction. The corrected CD signal is found to agree rather well with that for the same amount of Co-complex dispersed uniformly throughout the sample cell. This holds for different particle volume fractions and Co-complex concentrations inside the particles. The correction seems to work despite a substantial scattering contribution to the absorbance, which is not considered in the theoretical models.

  10. Absorption and scattering by bispheres, quadspheres, and circular rings of spheres and their equivalent coated spheres.

    PubMed

    Heng, Ri-Liang; Sy, Ki Cheong; Pilon, Laurent

    2015-01-01

    This study demonstrates that the absorption and scattering cross sections and asymmetry factor of randomly oriented and optically soft bispheres, quadspheres, and circular rings of spheres, with either monodisperse or polydisperse monomers, can be approximated by an equivalent coated sphere with identical volume and average projected area. This approximation could also apply to the angle-dependent scattering matrix elements for monomer size parameter less than 0.1. However, it quickly deteriorated with increasing monomer number and/or size parameter. It was shown to be superior to previously proposed approximations considering a volume equivalent homogeneous sphere and a coated sphere with identical volume and surface area. These results provide a rapid and accurate way of predicting the radiation characteristics of bispheres, quadspheres, and rings of spheres representative of various unicellular and multicellular cyanobacteria considered for producing food supplements, biofuels, and fertilizers. They could also be used in inverse methods for retrieving the monomers' optical properties, morphology, and/or concentration.

  11. Analyses of optical absorption and circular dichroism spectra of spinach ferredoxin at alkaline pH.

    PubMed

    Hasumi, H

    1982-10-01

    The whole protein structure and the microenvironments of the iron-sulfur cluster and of the side chains of amino acid residues of spinach ferredoxin were studied by optical absorption and circular dichroism (CD) spectroscopy in the alkaline pH range. From the pH-dependence of the optical absorption changes at 245 nm, the four tyrosyl residues of ferredoxin were classified into three groups: one exposed residue with a normal apparent pK value of 10.1, two exposed residues with abnormal apparent pK values of 12.0, and one buried residue showing time-dependent ionization. The absorption in the visible region disappeared gradually with the ionization of the buried residue rather than that of the three exposed residues. The apparent pK value of 10.0 was obtained from the rapid CD changes at 258 nm caused by pH elevation from neutral to alkaline pH. The structural alteration associated with the CD change had no effect on the secondary structure of the protein moiety other than the iron-sulfur cluster and the microenvironment of the cluster. The rate constants obtained from the time courses of the CD changes in the near-ultraviolet and visible regions were in good agreement with those obtained from the time courses of the optical absorption changes. These results lead to the conclusions that (1) the native ferredoxin structure is maintained through the interaction with the iron-sulfur cluster and (2) the protein structure in the neighborhood of the cluster, important for the physiological activity, is not perturbed even though the exposed tyrosyl residues are ionized.

  12. A new soft X-ray magnetic circular dichroism facility at the BSRF beamline 4B7B

    NASA Astrophysics Data System (ADS)

    Guo, Zhi-Ying; Hong, Cai-Hao; Xing, Hai-Ying; Tang, Kun; Zheng, Lei; Xui, Wei; Chen, Dong-Liang; Cui, Ming-Qi; Zhao, Yi-Dong

    2015-04-01

    X-ray magnetic circular dichroism (XMCD) has become an important and powerful tool because it allows the study of material properties in combination with elemental specificity, chemical state specificity, and magnetic specificity. A new soft X-ray magnetic circular dichroism apparatus has been developed at the Beijing Synchrotron Radiation Facility (BSRF). The apparatus combines three experimental conditions: an ultra-high-vacuum environment, moderate magnetic fields and in-situ sample preparation to measure the absorption signal. We designed a C-type dipole electromagnet that provides magnetic fields up to 0.5 T in parallel (or anti-parallel) direction relative to the incoming X-ray beam. The performances of the electromagnet are measured and the results show good agreement with the simulation ones. Following film grown in situ by evaporation methods, XMCD measurements are performed. Combined polarization corrections, the magnetic moments of the Fe and Co films determined by sum rules are consistent with other theoretical predictions and experimental measurements. Supported by National Natural Science Foundation of China (61204008)

  13. Binding of anti-prion agents to glycosaminoglycans: Evidence from electronic absorption and circular dichroism spectroscopy

    SciTech Connect

    Zsila, Ferenc . E-mail: zsferi@chemres.hu; Gedeon, Gabor

    2006-08-11

    The polyanionic glycosaminoglycans (GAGs) are intimately involved in the pathogenesis of protein conformational disorders such as amyloidosis and prion diseases. Several cationic agents are known to exhibit anti-prion activity but their mechanism of action is poorly understood. In this study, UV absorption and circular dichroism (CD) spectroscopic techniques were used to investigate the interaction between heparin and chondroitin-6-sulfate and anti-prion drugs including acridine, quinoline, and phenothiazine derivatives. UV band hypochromism of ({+-})-quinacrine, ({+-})-primaquine, tacrine, quinidine, chlorpromazine, and induced CD spectra of ({+-})-quinacrine upon addition of GAGs provided evidence for the GAG binding of these compounds. The association constants ({approx}10{sup 6}-10{sup 7} M{sup -1}) estimated from the UV titration curves show high-affinity drug-heparin interactions. Ionic strength-dependence of the absorption spectra suggested that the interaction between GAGs and the cationic drugs is principally electrostatic in nature. Drug binding differences of heparin and chondroitin-6-sulfate were attributed to their different negative charge density. These results call the attention to the alteration of GAG-prion/GAG-amyloid interactions by which these compounds might exert their anti-prion/anti-amyloidogenic activities.

  14. Circularly polarized Magnetic Field of Whistler Wave during Fast Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Zhai, Xiang; Wongwaitayakornkul, Pakorn; Bellan, Paul; Bellan Group Team

    2014-10-01

    Obliquely propagating whistler waves are expected to have circularly polarized magnetic components and to be associated with fast magnetic reconnection. In the Caltech plasma jet experiment, a current-carrying collimated jet is created from the merging of eight plasma-filled flux ropes. Fast magnetic reconnection occurs during the merging process. When the current- carrying jet undergoes fast kink instability, a lateral Rayleigh-Taylor instability occurs on the jet surface and induces another fast magnetic reconnection event. A capacitive coupling probe placed near the jet has measured fast electric field fluctuations at 15MHz which is in the whistler regime for this plasma. A 3D fast Bdot probe with good electrostatic rejection has been specifically designed to measure the 3D magnetic components of the whistler wave. Preliminary results have revealed a 3D 15 MHz magnetic fluctuation. Work is underway to increase the sensitivity of the induction probe and also to reduce electrostatic pickup. With the improved probe, the polarization property of the magnetic component of the whistler wave is expected to be resolved if it exists.

  15. Magnetic properties of transition-metal multilayers studied with x-ray magnetic circular dichroism spectroscopy

    SciTech Connect

    Stoehr, J.; Nakajima, R.

    1998-01-01

    The detailed understanding of the magnetic properties of transition-metal multilayers requires the use of state-of-the-art experimental techniques. Over the last few years, the X-ray magnetic circular dichroism (XMCD) technique has evolved into an important magnetometry tool. This paper is an overview of the principles and unique strengths of the technique. Aspects covered include the quantitative determination of element-specific spin and orbital magnetic moments and their anisotropies through sumrule analyses of experimental spectra. A discussion is presented on how the spin and orbital magnetic moments in transition-metal thin films and sandwiches are modified relative to the bulk. The authors show that a thin film of a nonmagnetic metal such as Cu may become magnetically active when adjacent to a magnetic layer, and a thin film of a ferromagnetic metal such as Fe may become magnetically inactive. The orbital moment is found to become anisotropic in thin films; it can be regarded as the microscopic origin of the magnetocrystalline anisotropy.

  16. Scanning magnetic microscopy model analysis of circular flaws in thin metallic plates

    NASA Astrophysics Data System (ADS)

    Adamo, M.; Calvano, F.; Nappi, C.; Sarnelli, E.

    2009-12-01

    We studied the eddy currents excited by a time varying external magnetic field in thin metallic plates in the presence of a circular hole piercing the plate. The value of the normal component of the magnetic field over the circular defect is analytically calculated and a complete scanning magnetic operation along a line crossing the defect is simulated. The analytical solution is then tested against a direct numerical simulation with good results. The aim is the reconstruction and interpretation of magnetic signatures due to structural defects in nondestructive evaluation made by superconducting quantum interference device microscopy measurements.

  17. Binary information propagation in circular magnetic nanodot arrays using strain induced magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Salehi-Fashami, M.; Al-Rashid, M.; Sun, Wei-Yang; Nordeen, P.; Bandyopadhyay, S.; Chavez, A. C.; Carman, G. P.; Atulasimha, J.

    2016-10-01

    Nanomagnetic logic has emerged as a potential replacement for traditional Complementary Metal Oxide Semiconductor (CMOS) based logic because of superior energy-efficiency (Salahuddin and Datta 2007 Appl. Phys. Lett. 90 093503, Cowburn and Welland 2000 Science 287 1466-68). One implementation of nanomagnetic logic employs shape-anisotropic (e.g. elliptical) ferromagnets (with two stable magnetization orientations) as binary switches that rely on dipole-dipole interaction to communicate binary information (Cowburn and Welland 2000 Science 287 1466-8, Csaba et al 2002 IEEE Trans. Nanotechnol. 1 209-13, Carlton et al 2008 Nano Lett. 8 4173-8, Atulasimha and Bandyopadhyay 2010 Appl. Phys. Lett. 97 173105, Roy et al 2011 Appl. Phys. Lett. 99 063108, Fashami et al 2011 Nanotechnology 22 155201, Tiercelin et al 2011 Appl. Phys. Lett. 99 , Alam et al 2010 IEEE Trans. Nanotechnol. 9 348-51 and Bhowmik et al 2013 Nat. Nanotechnol. 9 59-63). Normally, circular nanomagnets are incompatible with this approach since they lack distinct stable in-plane magnetization orientations to encode bits. However, circular magnetoelastic nanomagnets can be made bi-stable with a voltage induced anisotropic strain, which provides two significant advantages for nanomagnetic logic applications. First, the shape-anisotropy energy barrier is eliminated which reduces the amount of energy required to reorient the magnetization. Second, the in-plane size can be reduced (˜20 nm) which was previously not possible due to thermal stability issues. In circular magnetoelastic nanomagnets, a voltage induced strain stabilizes the magnetization even at this size overcoming the thermal stability issue. In this paper, we analytically demonstrate the feasibility of a binary ‘logic wire’ implemented with an array of circular nanomagnets that are clocked with voltage-induced strain applied by an underlying piezoelectric substrate. This leads to an energy-efficient logic paradigm orders of magnitude superior to

  18. Binary information propagation in circular magnetic nanodot arrays using strain induced magnetic anisotropy.

    PubMed

    Salehi-Fashami, M; Al-Rashid, M; Sun, Wei-Yang; Nordeen, P; Bandyopadhyay, S; Chavez, A C; Carman, G P; Atulasimha, J

    2016-10-28

    Nanomagnetic logic has emerged as a potential replacement for traditional Complementary Metal Oxide Semiconductor (CMOS) based logic because of superior energy-efficiency (Salahuddin and Datta 2007 Appl. Phys. Lett. 90 093503, Cowburn and Welland 2000 Science 287 1466-68). One implementation of nanomagnetic logic employs shape-anisotropic (e.g. elliptical) ferromagnets (with two stable magnetization orientations) as binary switches that rely on dipole-dipole interaction to communicate binary information (Cowburn and Welland 2000 Science 287 1466-8, Csaba et al 2002 IEEE Trans. Nanotechnol. 1 209-13, Carlton et al 2008 Nano Lett. 8 4173-8, Atulasimha and Bandyopadhyay 2010 Appl. Phys. Lett. 97 173105, Roy et al 2011 Appl. Phys. Lett. 99 063108, Fashami et al 2011 Nanotechnology 22 155201, Tiercelin et al 2011 Appl. Phys. Lett. 99 , Alam et al 2010 IEEE Trans. Nanotechnol. 9 348-51 and Bhowmik et al 2013 Nat. Nanotechnol. 9 59-63). Normally, circular nanomagnets are incompatible with this approach since they lack distinct stable in-plane magnetization orientations to encode bits. However, circular magnetoelastic nanomagnets can be made bi-stable with a voltage induced anisotropic strain, which provides two significant advantages for nanomagnetic logic applications. First, the shape-anisotropy energy barrier is eliminated which reduces the amount of energy required to reorient the magnetization. Second, the in-plane size can be reduced (∼20 nm) which was previously not possible due to thermal stability issues. In circular magnetoelastic nanomagnets, a voltage induced strain stabilizes the magnetization even at this size overcoming the thermal stability issue. In this paper, we analytically demonstrate the feasibility of a binary 'logic wire' implemented with an array of circular nanomagnets that are clocked with voltage-induced strain applied by an underlying piezoelectric substrate. This leads to an energy-efficient logic paradigm orders of magnitude superior to

  19. Binary information propagation in circular magnetic nanodot arrays using strain induced magnetic anisotropy.

    PubMed

    Salehi-Fashami, M; Al-Rashid, M; Sun, Wei-Yang; Nordeen, P; Bandyopadhyay, S; Chavez, A C; Carman, G P; Atulasimha, J

    2016-10-28

    Nanomagnetic logic has emerged as a potential replacement for traditional Complementary Metal Oxide Semiconductor (CMOS) based logic because of superior energy-efficiency (Salahuddin and Datta 2007 Appl. Phys. Lett. 90 093503, Cowburn and Welland 2000 Science 287 1466-68). One implementation of nanomagnetic logic employs shape-anisotropic (e.g. elliptical) ferromagnets (with two stable magnetization orientations) as binary switches that rely on dipole-dipole interaction to communicate binary information (Cowburn and Welland 2000 Science 287 1466-8, Csaba et al 2002 IEEE Trans. Nanotechnol. 1 209-13, Carlton et al 2008 Nano Lett. 8 4173-8, Atulasimha and Bandyopadhyay 2010 Appl. Phys. Lett. 97 173105, Roy et al 2011 Appl. Phys. Lett. 99 063108, Fashami et al 2011 Nanotechnology 22 155201, Tiercelin et al 2011 Appl. Phys. Lett. 99 , Alam et al 2010 IEEE Trans. Nanotechnol. 9 348-51 and Bhowmik et al 2013 Nat. Nanotechnol. 9 59-63). Normally, circular nanomagnets are incompatible with this approach since they lack distinct stable in-plane magnetization orientations to encode bits. However, circular magnetoelastic nanomagnets can be made bi-stable with a voltage induced anisotropic strain, which provides two significant advantages for nanomagnetic logic applications. First, the shape-anisotropy energy barrier is eliminated which reduces the amount of energy required to reorient the magnetization. Second, the in-plane size can be reduced (∼20 nm) which was previously not possible due to thermal stability issues. In circular magnetoelastic nanomagnets, a voltage induced strain stabilizes the magnetization even at this size overcoming the thermal stability issue. In this paper, we analytically demonstrate the feasibility of a binary 'logic wire' implemented with an array of circular nanomagnets that are clocked with voltage-induced strain applied by an underlying piezoelectric substrate. This leads to an energy-efficient logic paradigm orders of magnitude superior to

  20. Applications of circularly polarized photons at the ALS with a bend magnet source

    SciTech Connect

    Not Available

    1992-02-01

    The purpose of this workshop is to focus attention on, and to stimulate the scientific exploitation of, the natural polarization properties of bend-magnet synchrotron radiation at the ALS -- for research in biology, materials science, physics, and chemistry. The topics include: The Advanced Light Source; Magnetic Circular Dichroism and Differential Scattering on Biomolecules; Tests of Fundamental Symmetries; High {Tc} Superconductivity; Photoemission from Magnetic and Non-magnetic Solids; Studies of Highly Correlated Systems; and Instrumentation for Photon Transport and Polarization Measurements.

  1. Direct observation of depth profile of magnetic moment by magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Mun, Bongjin Simon; Yang, See-Hun; Mannella, Norman; Kay, Alex W.; Kim, Sang-Koog; Kortright, Jeffrey B.; Underwood, Jim H.; Hussain, Zahid; Fadley, Charles S.

    2001-03-01

    The magnetic properties at the interface between Fe and Cr wedge layers are investigated with a new depth-resolved soft x-ray photoemission spectroscopy (SXPS)[1], combined with magnetic circular dichroism (MCD). The layers of Fe (10 A)/ Cr (50 A wedge- shaped) are grown on a periodic multilayer (B 4 C(22.5A)/W(17.1 A)) _40, which provides the strong standing wave effects of 40 The unique angular dependence of photoelectron intensity of Fe and Cr has been observed at each different Cr wedge thickness and show excellent agreement with the theoretical calculation. To maximize the enhancement and contrast of standing wave effect inside of sample, the sample position is tuned to the Bragg angle position, at which the MCD measurement with SXPS along the different thickness of Cr wedge layer provides the depth profile of the magnetic moment of Fe and Cr. A strong antiparallel coupling across the interface of Cr magnetic moment is clearly resolved while the apparent reduction of Fe magnetic moment is observed near the interface. This observation is consistent with the other works on the same system [2] and even describes how the magnetic moment behaves inside of the sample from the top surface to the interface in one single sample preparation. In this experiment, a new depth-resolved SXPS has been successfully implemented to magnetic multilayer system and prove to be powerful technique to study the buried interface of magnetic system, as proposed by our former work [1]. [1] S.-H. Yang, B. S. Mun, A.W. Kay, S.-K. Kim, J. B. Kortright , J.H. Underwood, Z. Hussain, C. S. Fadley, Surf. Sci. 461 L557-L564 (2000) [2] G. Panaccione, F. Sirotti, E. Narducci, and G. Rossi, Phys. Rev. B 55, 389 (1997)

  2. Circular Samples as Objects for Magnetic Resonance Imaging - Mathematical Simulation, Experimental Results

    NASA Astrophysics Data System (ADS)

    Frollo, Ivan; Krafčík, Andrej; Andris, Peter; Přibil, Jiří; Dermek, Tomáš

    2015-12-01

    Circular samples are the frequent objects of "in-vitro" investigation using imaging method based on magnetic resonance principles. The goal of our investigation is imaging of thin planar layers without using the slide selection procedure, thus only 2D imaging or imaging of selected layers of samples in circular vessels, eppendorf tubes,.. compulsorily using procedure "slide selection". In spite of that the standard imaging methods was used, some specificity arise when mathematical modeling of these procedure is introduced. In the paper several mathematical models were presented that were compared with real experimental results. Circular magnetic samples were placed into the homogenous magnetic field of a low field imager based on nuclear magnetic resonance. For experimental verification an MRI 0.178 Tesla ESAOTE Opera imager was used.

  3. Absorption and scattering by bispheres, quadspheres, and circular rings of spheres and their equivalent coated spheres.

    PubMed

    Heng, Ri-Liang; Sy, Ki Cheong; Pilon, Laurent

    2015-01-01

    This study demonstrates that the absorption and scattering cross sections and asymmetry factor of randomly oriented and optically soft bispheres, quadspheres, and circular rings of spheres, with either monodisperse or polydisperse monomers, can be approximated by an equivalent coated sphere with identical volume and average projected area. This approximation could also apply to the angle-dependent scattering matrix elements for monomer size parameter less than 0.1. However, it quickly deteriorated with increasing monomer number and/or size parameter. It was shown to be superior to previously proposed approximations considering a volume equivalent homogeneous sphere and a coated sphere with identical volume and surface area. These results provide a rapid and accurate way of predicting the radiation characteristics of bispheres, quadspheres, and rings of spheres representative of various unicellular and multicellular cyanobacteria considered for producing food supplements, biofuels, and fertilizers. They could also be used in inverse methods for retrieving the monomers' optical properties, morphology, and/or concentration. PMID:26366489

  4. Plastocyanin conformation: an analysis of its near ultraviolet absorption and circular dichroic spectra

    SciTech Connect

    Draheim, J.E.; Anderson, G.P.; Duane, J.W.; Gross, E.L.

    1986-04-01

    The near-ultraviolet absorption and circular dichroic spectra of plastocyanin are dependent upon the redox state, solution pH, and ammonium sulfate concentration. This dependency was observed in plastocyanin isolated from spinach, poplar, and lettuce. Removal of the copper atom also perturbed the near-ultraviolet spectra. Upon reduction there are increases in both extinction and ellipticity at 252 nm. Further increases at 252 nm were observed upon formation of apo plastocyanin eliminating charge transfer transitions as the cause. The spectral changes in the near-ultraviolet imply a flexible tertiary conformation for plastocyanin. There are at least two charge transfer transitions at approx.295-340 nm. One of these transitions is sensitive to low pH's and is attributed to the His 87 copper ligand. The redox state dependent changes observed in the near-ultraviolet spectra of plastocyanin are attenuated either by decreasing the pH to 5 or by increasing the ammonium sulfate concentration to 2.7 M. This attenuation cannot be easily explained by simple charge screening. Hydrophobic interactions probably play an important role in this phenomenon. The pH and redox state dependent conformational changes may play an important role in regulating electron transport.

  5. Angle and temperature dependence of magnetic circular dichroism in core-level photoemission from Gd(0001)

    SciTech Connect

    Denecke, R.; Morais, J.; Ynzunza, R. X.; Menchero, J. G.; Liesegang, J.; Rice, M.; Kortright, J.; Hussain, Z.; Fadley, C. S.

    1997-04-01

    Magnetic dichroism in core-level photoelectron emission from solids represents a promising new element-specific probe of surface and interface atomic structure and magnetic order. One way of measuring such effects is by using photoelectrons excited by circular polarized radiation, thus leading to magnetic circular dichroism (MCD) if the intensity with right-circular polarized (RCP) light is not equal to that with left-circular polarized (LCP) light. The spin-integrated photoelectron intensity in a certain emission direction also in general depends on the direction of the magnetization in a magnetic material. In fact, if the magnetization lies in a surface mirror plane, then inverting its direction can provide a second way of measuring MCD. Purely atomic theoretical models have been successful in explaining many aspects of such data. By varying the emission direction one also probes the geometric structure of the sample. But such MCD in photoelectron angular distributions (MCDAD) then has to be interpreted also in terms of photoelectron diffraction. Measuring the temperature dependence of such MCD effects also provides a useful tool for studying magnetic transition temperatures. The authors have here studied such effects in core-level emission from Gd(0001).

  6. Magnetization reversal assisted by half antivortex states in nanostructured circular cobalt disks

    SciTech Connect

    Lara, A.; Aliev, F. G.; Dobrovolskiy, O. V.; Prieto, J. L.; Huth, M.

    2014-11-03

    The half antivortex, a fundamental topological structure which determines magnetization reversal of submicron magnetic devices with domain walls, has been suggested also to play a crucial role in spin torque induced vortex core reversal in circular disks. Here, we report on magnetization reversal in circular disks with nanoholes through consecutive metastable states with half antivortices. In-plane anisotropic magnetoresistance and broadband susceptibility measurements accompanied by micromagnetic simulations reveal that cobalt (Co) disks with two and three linearly arranged nanoholes directed at 45° and 135° with respect to the external magnetic field show reproducible step-like changes in the anisotropic magnetoresistance and magnetic permeability due to transitions between different intermediate states mediated by vortices and half antivortices confined to the dot nanoholes and edges, respectively. Our findings are relevant for the development of multi-hole based spintronic and magnetic memory devices.

  7. Element and orbital-specific observation of two-step magnetic transition in NpNiGa5 : X-ray magnetic circular dichroism study

    NASA Astrophysics Data System (ADS)

    Okane, T.; Ohkochi, T.; Inami, T.; Takeda, Y.; Fujimori, S.-I.; Kawamura, N.; Suzuki, M.; Tsutsui, S.; Yamagami, H.; Fujimori, A.; Tanaka, A.; Aoki, D.; Homma, Y.; Shiokawa, Y.; Yamamoto, E.; Haga, Y.; Nakamura, A.; Ōnuki, Y.

    2009-09-01

    X-ray magnetic circular dichroism (XMCD) experiments were performed at the NpM4,5 and the GaK absorption edges of NpNiGa5 to investigate the temperature-dependent changes of magnetic properties of Np5f and Ga4p electron states. By the sum-rule analysis of the NpM4,5 XMCD data, the orbital magnetic moment μL and the spin magnetic moment μS were estimated for the Np5f3 and 5f4 electronic configurations and their comparison to the previous magnetization and neutron-scattering experiments suggests that the 5f4 configuration is more likely than the 5f3 configuration in NpNiGa5 . It was found that |μL/μS| tends to increase from the high-temperature low-moment ordered state to the low-temperature high-moment ordered state. The result of the GaK XMCD indicates that the Ga4p electrons are magnetically polarized and the temperature and magnetic-field dependences of the Ga4p orbital moment are proportional to those of the magnetization measurements.

  8. Inertial spin alignment in a circular magnetic nanotube

    NASA Astrophysics Data System (ADS)

    Bergmann, Gerd; Thompson, Richard S.; Lu, Jia G.

    2015-09-01

    In cobalt nanotubes with a curling magnetization, the orbital motion of the conduction electrons interacts with their spin. As the spin goes around the nanotube it cannot follow the magnetization, since with the Fermi velocity it moves too fast. Instead, we predict that the spin precesses about an axis that is almost parallel to the axis of the nanotube and that rotates with the angular velocity of the electron. Therefore, the (absolute) value of the magnetic energy of the spin | μ ṡ B | is strongly reduced. The physics of the ferromagnet is considerably modified.

  9. ABSORPTION OF p MODES BY THIN MAGNETIC FLUX TUBES

    SciTech Connect

    Jain, Rekha; Hindman, Bradley W.; Braun, Doug C.; Birch, Aaron C.

    2009-04-10

    We study the interaction between p modes and the many magnetic fibrils that lace the solar convection zone. In particular, we investigate the resulting absorption of p-mode energy by the fibril magnetic field. Through mechanical buffeting, the p modes excite tube waves on the magnetic fibrils-in the form of longitudinal sausage waves and transverse kink waves. The tube waves propagate up and down the magnetic fibrils and out of the p-mode cavity, thereby removing energy from the incident acoustic waves. We compute the absorption coefficient associated with this damping mechanism and model the absorption that would be observed for magnetic plage. We compare our results to the absorption coefficient that is measured using the local-helioseismic technique of ridge-filtered holography. We find that, depending on the mode order and the photospheric boundary conditions, we can achieve absorption coefficients for simulated plage that exceed 50%. The observed increase of the absorption coefficient as a function of frequency is reproduced for all model parameters.

  10. Experiments on Inductive Magnetic Levitation with a Circular Halbach Array

    NASA Astrophysics Data System (ADS)

    Bean, Ian; Goncz, Doug; Raymer, Austin; Specht, Jason; Zalles, Ricardo; Majewski, Walerian

    2013-03-01

    Using a ring Halbach array, we are investigating a repulsive levitating force and a drag force acting on the magnet from a ring of inductors rotating below the magnet. After measuring induced currents, voltages and magnetic fields in the individual inductors (in the form of short solenoids), we investigated the dependence of lift/drag forces on the speed of relative rotation. The ratio of lift to drag increases with the angular velocity, as expected from a related theory of the induction effects in a linear motion. We are experimenting with the shape and density of inductors, and their material, in an attempt to maximize the lift at a minimal velocity of rotation. Eventually this design could have applications as frictionless bearings or as frictionless gear in a wide range of systems, especially in machinery that cannot be easily accessed.

  11. Magnetic Circular Dichroism Studies XXV. A Preliminary Investigation of Microsomal Cytochromes*

    PubMed Central

    Dolinger, Peter M.; Kielczewski, Michael; Trudell, James R.; Barth, Günter; Linder, Robert E.; Bunnenberg, Edward; Djerassi, Carl

    1974-01-01

    The application of magnetic circular dichroism as an optical probe for simultaneous identification and determination of at least two microsomal cytochromes is demonstrated. The assignments of the bands in the spectra of microsomal suspensions are made from the spectra of soluble preparations of cytochrome P-450 obtained from Pseudomonas putida and of cytochrome b5 obtained from rat livers. PMID:4521811

  12. X-ray magnetic circular dichroic magnetometry on Ni/Pt multilayers

    NASA Astrophysics Data System (ADS)

    Poulopoulos, P.; Wilhelm, F.; Wende, H.; Ceballos, G.; Baberschke, K.; Benea, D.; Ebert, H.; Angelakeris, M.; Flevaris, N. K.; Rogalev, A.; Brookes, N. B.

    2001-04-01

    X-ray magnetic circular dichroism measurements have been performed on Ni/Pt multilayers at a temperature of 10 K. The element specificity and shell selectivity of the technique allows us to probe Ni and Pt magnetic moments and to separate them into their constituent spin (μS) and orbital (μL) magnetic moments. The Ni magnetic moment at the interface is found to be reduced. However, magnetically "dead" Ni layers are unambiguously ruled out. Induced Pt magnetic moments up to about 0.3 μB/atom are reported. The results are compared to ab initio calculations and to previous experiments performed on NiPt alloys. The role of intermixing in the reduction of the Ni magnetic moments is also discussed.

  13. Near infrared light absorption in magnetic nanoemulsion under external magnetic field

    NASA Astrophysics Data System (ADS)

    Brojabasi, Surajit; Mahendran, V.; Lahiri, B. B.; Philip, John

    2014-07-01

    We study the magnetic field dependent near infrared photon absorption behavior in a magnetically polarizable oil-in-water emulsion of droplet radius ~110 nm. The absorption of near infrared photons in magnetic nanoemulsion is found to be dependent on the volume fraction and applied magnetic field, which is attributed to the variation in the Mie absorption efficiency during the structural transitions of nanoemulsion droplets in dispersion. Also, the absorption linearly increases with incident near infrared photon energy up to certain external magnetic field. The imaginary part of the refractive index (k1) of magnetic nanoemulsion obtained from the near infrared absorption profile in the Rayleigh regime is found to vary with external magnetic field and the sample volume fraction (ϕ). The measured k1 follows a power law increment with sample volume fraction (k1~ϕ, where p is the exponent). The exponent (p) decreases with external magnetic field implying that the structural transition of nanoemulsion droplets increases k1. After a critical magnetic field (beyond Rayleigh regime), field induced absorption of near infrared photons decreases because of the increase in the aspect ratio of the chain like aggregates and interchain spacing which in turn reduces the Mie absorption efficiency.

  14. Absorption spectra of graphene nanoribbons in a composite magnetic field

    NASA Astrophysics Data System (ADS)

    Li, T. S.; Wu, M. F.; Hsieh, C. T.

    2015-10-01

    The low-frequency optical absorption properties of graphene nanoribbons in a composite magnetic field are investigated by using the gradient approximation. The spectral function exhibits symmetric delta-function like prominent peaks structure in a uniform magnetic field, and changes to asymmetric square-root divergent peaks structure when subjecting to a composite field. These asymmetric divergent peaks can be further classified into principal and secondary peaks. The spectral intensity and frequency of the absorption peaks depend sensitively on the strength and modulation period of the composite field. The transition channels of the absorption peaks are also analyzed. There exists an optical selection rule which is caused by the orthogonal properties of the sublattice wave functions. The evolution of the spectral frequency of the absorption peaks with the field strength is explored.

  15. Polarization measurement and vertical aperture optimization for obtaining circularly polarized bend-magnet radiation

    SciTech Connect

    Kortright, J.B.; Rice, M.; Hussain, Z.

    1997-04-01

    Growing interest in utilizing circular polarization prompted the design of bend-magnet beamline 9.3.2 at the Advanced Light Source, covering the 30-1500 eV spectral region, to include vertical aperturing capabilities for optimizing the collection of circular polarization above and below the orbit plane. After commissioning and early use of the beamline, a multilayer polarimeter was used to characterize the polarization state of the beam as a function of vertical aperture position. This report partially summarizes the polarimetry measurements and compares results with theoretical calculations intended to simulate experimental conditions.

  16. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    SciTech Connect

    Miwa, Shinji Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige; Kotani, Yoshinori; Nakamura, Tetsuya

    2015-10-19

    In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.

  17. Circular current loops, magnetic dipoles and spherical harmonic analysis.

    USGS Publications Warehouse

    Alldredge, L.R.

    1980-01-01

    Spherical harmonic analysis (SHA) is the most used method of describing the Earth's magnetic field, even though spherical harmonic coefficients (SHC) almost completely defy interpretation in terms of real sources. Some moderately successful efforts have been made to represent the field in terms of dipoles placed in the core in an effort to have the model come closer to representing real sources. Dipole sources are only a first approximation to the real sources which are thought to be a very complicated network of electrical currents in the core of the Earth. -Author

  18. Degree of circular polarization in II-VI diluted magnetic semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Rana, Shivani; Sen, Pratima; Sen, Pranay Kumar

    2012-07-01

    Degree of circular polarization (DCP) in II-VI diluted magnetic semiconductor quantum dots (QDs) has been studied analytically. Energy levels have been calculated using Luttinger-Kohn Hamiltonian and effective mass approximation. Effects due to application of externa magnetic field have been investigated, followed by calculation of transition dipole moment and DCP. Numerical estimates made for Mn-doped CdSe/ZnSe QDs show that DCP in undoped QDs is negligible while transition metal ion doping yields substantial polarization rotation (≈-2.20%) even at moderate magnetic fields (≈0.5T).

  19. A Circular-cylindrical Flux-rope Analytical Model for Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Nieves-Chinchilla, T.; Linton, M. G.; Hidalgo, M. A.; Vourlidas, A.; Savani, N. P.; Szabo, A.; Farrugia, C.; Yu, W.

    2016-05-01

    We present an analytical model to describe magnetic flux-rope topologies. When these structures are observed embedded in Interplanetary Coronal Mass Ejections (ICMEs) with a depressed proton temperature, they are called Magnetic Clouds (MCs). Our model extends the circular-cylindrical concept of Hidalgo et al. by introducing a general form for the radial dependence of the current density. This generalization provides information on the force distribution inside the flux rope in addition to the usual parameters of MC geometrical information and orientation. The generalized model provides flexibility for implementation in 3D MHD simulations. Here, we evaluate its performance in the reconstruction of MCs in in situ observations. Four Earth-directed ICME events, observed by the Wind spacecraft, are used to validate the technique. The events are selected from the ICME Wind list with the magnetic obstacle boundaries chosen consistently with the magnetic field and plasma in situ observations and with a new parameter (EPP, the Electron Pitch angle distribution Parameter) which quantifies the bidirectionally of the plasma electrons. The goodness of the fit is evaluated with a single correlation parameter to enable comparative analysis of the events. In general, at first glance, the model fits the selected events very well. However, a detailed analysis of events with signatures of significant compression indicates the need to explore geometries other than the circular-cylindrical. An extension of our current modeling framework to account for such non-circular CMEs will be presented in a forthcoming publication.

  20. ON THE 2012 OCTOBER 23 CIRCULAR RIBBON FLARE: EMISSION FEATURES AND MAGNETIC TOPOLOGY

    SciTech Connect

    Yang, Kai; Guo, Yang; Ding, M. D. E-mail: dmd@nju.edu.cn

    2015-06-20

    Circular ribbon flares are usually related to spine-fan type magnetic topology containing null points. In this paper, we investigate an X-class circular ribbon flare on 2012 October 23, using the multiwavelength data from the Solar Dynamics Observatory, Hinode, and RHESSI. In Ca ii H emission, the flare showed three ribbons with two highly elongated ones inside and outside a quasi-circular one, respectively. A hot channel was displayed in the extreme-ultraviolet emissions that infers the existence of a magnetic flux rope. Two hard X-ray (HXR) sources in the 12–25 keV energy band were located at the footpoints of this hot channel. Using a nonlinear force-free magnetic field extrapolation, we identify three topological structures: (1) a three-dimensional null point, (2) a flux rope below the fan of the null point, and (3) a large-scale quasi-separatrix layer (QSL) induced by the quadrupolar-like magnetic field of the active region. We find that the null point is embedded within the large-scale QSL. In our case, all three identified topological structures must be considered to explain all the emission features associated with the observed flare. Besides, the HXR sources are regarded as the consequence of the reconnection within or near the border of the flux rope.

  1. Embedding Circular Force-Free Flux Ropes in Potential Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Titov, V. S.; Torok, T.; Mikic, Z.; Linker, J.

    2013-12-01

    We propose a method for constructing approximate force-free equilibria in active regions that locally have a potential bipolar-type magnetic field with a thin force-free flux rope embedded inside it. The flux rope has a circular-arc axis and circular cross-section in which the interior magnetic field is predominantly toroidal (axial). Its magnetic pressure is balanced outside by that of the poloidal (azimuthal) field created at the boundary by the electric current sheathing the flux rope. To facilitate the implementation of the method in our numerical magnetohydrodynamic (MHD) code, the entire solution is described in terms of the vector potential of the magnetic field. The parameters of the flux rope can be chosen so that a subsequent MHD relaxation of the constructed configuration under line-tied conditions at the boundary provides a numerically exact equilibrium. Such equilibria are an approximation for the magnetic configuration preceding solar eruptions, which can be triggered in our model by imposing suitable photospheric flows beneath the flux rope. The proposed method is a useful tool for constructing pre-eruption magnetic fields in data-driven simulations of solar active events. Research supported by NASA's Heliophysics Theory and LWS Programs, and NSF/SHINE and NSF/FESD.

  2. Simulation of Vacuum UV Absorption and Electronic Circular Dichroism Spectra of Methyl Oxirane: The Role of Vibrational Effects.

    PubMed

    Hodecker, Manuel; Biczysko, Malgorzata; Dreuw, Andreas; Barone, Vincenzo

    2016-06-14

    Vibrationally resolved one-photon absorption and electronic circular dichroism spectra of (R)-methyl oxirane were calculated with different electronic and vibronic models selecting, through an analysis of the convergence of the results, the best compromise between reliability and computational cost. Linear-response TD-DFT/CAM-B3LYP/SNST electronic computations in conjunction with the simple vertical gradient vibronic model were chosen and employed for systematic comparison with the available experimental data. Remarkable agreement between simulated and experimental spectra was achieved for both one-photon absorption and circular dichroism concerning peak positions, relative intensities, and general spectral shapes considering the computational efficiency of the chosen theoretical approach. The significant improvement of the results with respect to smearing of vertical electronic transitions by phenomenological Gaussian functions and the possible inclusion of solvent effects by polarizable continuum models at a negligible additional cost paves the route toward the simulation and analysis of spectral shapes of complex molecular systems in their natural environment. PMID:27159495

  3. Ground-state wave function of plutonium in PuSb as determined via x-ray magnetic circular dichroism

    SciTech Connect

    Janoschek, M.; Haskel, D.; Fernandez-Rodriguez, J.; van Veenendaal, M.; Rebizant, J.; Lander, G. H.; Zhu, J. -X.; Thompson, J. D.; Bauer, E. D.

    2015-01-14

    Measurements of x-ray magnetic circular dichroism (XMCD) and x-ray absorption near-edge structure (XANES) spectroscopy at the Pu M₄,₅ edges of the ferromagnet PuSb are reported. Using bulk magnetization measurements and a sum rule analysis of the XMCD spectra, we determine the individual orbital [μL = 2.8(1)μB/Pu] and spin moments [μS = –2.0(1)μB/Pu] of the Pu 5f electrons for the first time. Atomic multiplet calculations of the XMCD and XANES spectra reproduce well the experimental data and are consistent with the experimental value of the spin moment. These measurements of Lz and Sz are in excellent agreement with the values that have been extracted from neutron magnetic form factor measurements, and confirm the local character of the 5f electrons in PuSb. We demonstrate that a split M₅ as well as a narrow M₄ XMCD signal may serve as a signature of 5f electron localization in actinide compounds.

  4. Ground-state wave function of plutonium in PuSb as determined via x-ray magnetic circular dichroism

    DOE PAGES

    Janoschek, M.; Haskel, D.; Fernandez-Rodriguez, J.; van Veenendaal, M.; Rebizant, J.; Lander, G. H.; Zhu, J. -X.; Thompson, J. D.; Bauer, E. D.

    2015-01-14

    Measurements of x-ray magnetic circular dichroism (XMCD) and x-ray absorption near-edge structure (XANES) spectroscopy at the Pu M₄,₅ edges of the ferromagnet PuSb are reported. Using bulk magnetization measurements and a sum rule analysis of the XMCD spectra, we determine the individual orbital [μL = 2.8(1)μB/Pu] and spin moments [μS = –2.0(1)μB/Pu] of the Pu 5f electrons for the first time. Atomic multiplet calculations of the XMCD and XANES spectra reproduce well the experimental data and are consistent with the experimental value of the spin moment. These measurements of Lz and Sz are in excellent agreement with the values thatmore » have been extracted from neutron magnetic form factor measurements, and confirm the local character of the 5f electrons in PuSb. We demonstrate that a split M₅ as well as a narrow M₄ XMCD signal may serve as a signature of 5f electron localization in actinide compounds.« less

  5. Room-temperature ferromagnetism of Cu-doped ZnO films probed by soft X-ray magnetic circular dichroism.

    PubMed

    Herng, T S; Qi, D-C; Berlijn, T; Yi, J B; Yang, K S; Dai, Y; Feng, Y P; Santoso, I; Sánchez-Hanke, C; Gao, X Y; Wee, Andrew T S; Ku, W; Ding, J; Rusydi, A

    2010-11-12

    We report direct evidence of room-temperature ferromagnetic ordering in O-deficient ZnO:Cu films by using soft x-ray magnetic circular dichroism and x-ray absorption. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu2+ ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V(O)) and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order. Based on first-principles calculations, we propose a microscopic "indirect double-exchange" model, in which alignments of localized large moments of Cu in the vicinity of the V(O) are mediated by the large-sized vacancy orbitals.

  6. Room-Temperature Ferromagnetism of Cu-Doped ZnO Films Probed by Soft X-Ray Magnetic Circular Dichroism

    SciTech Connect

    Herng, T.S.; Ku, W.; Qi, D.-C.; Berlijn, T.; Yi, J.B.; Yang, K.S.; Dai, Y.; Feng, Y.P.; Santoso, I.; Sanchez-Hanke, C.; Gao, X.Y.; Wee, A.T.S.; Ding, J.; Rusydi, A.

    2010-11-08

    We report direct evidence of room-temperature ferromagnetic ordering in O-deficient ZnO:Cu films by using soft x-ray magnetic circular dichroism and x-ray absorption. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu{sup 2+} ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V{sub O}) and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order. Based on first-principles calculations, we propose a microscopic 'indirect double-exchange' model, in which alignments of localized large moments of Cu in the vicinity of the V{sub O} are mediated by the large-sized vacancy orbitals.

  7. Direct observation of high-spin states in manganese dimer and trimer cations by x-ray magnetic circular dichroism spectroscopy in an ion trap

    SciTech Connect

    Zamudio-Bayer, V.; Hirsch, K.; Langenberg, A.; Kossick, M.; Ławicki, A.; Lau, J. T.; Terasaki, A.; Issendorff, B. von

    2015-06-21

    The electronic structure and magnetic moments of free Mn{sub 2}{sup +} and Mn{sub 3}{sup +} are characterized by 2p x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap that is coupled to a synchrotron radiation beamline. Our results directly show that localized magnetic moments of 5 μ{sub B} are created by 3d{sup 5}({sup 6}S) states at each ionic core, which are coupled ferromagnetically to form molecular high-spin states via indirect exchange that is mediated in both cases by a delocalized valence electron in a singly occupied 4s derived antibonding molecular orbital with an unpaired spin. This leads to total magnetic moments of 11 μ{sub B} for Mn{sub 2}{sup +} and 16 μ{sub B} for Mn{sub 3}{sup +}, with no contribution of orbital angular momentum.

  8. Magnetic circular x-ray dichroisms of Fe-Ni alloys at K edge.

    SciTech Connect

    Freeman, A. J.; Gofron, K. J.; Kimball, C. W.; Lee, P. L.; Montano, P. A.; Rao, F.; Wang, X.

    1997-04-03

    Magnetic Circular X-ray Dichroism (MCXD) studies at K edges of Fe-Ni alloys reveal changes of the MCXD signal with composition and crystal structure. We observe that the signal at the invar composition is of comparable strength as other compositions. Moreover, the edge position is strongly dependent on lattice constant. First principles calculations demonstrate that the shape and strength of the signal strongly depends on the crystal orientation, composition, and lattice constant. We find direct relation between the MCXD signal and the p DOS. We find that the MCXD at K edge probes the magnetism due to itinerant electrons.

  9. A novel design of iron dominated superconducting multipole magnets with circular coils

    SciTech Connect

    Kashikhin, Vladimir; /Fermilab

    2009-10-01

    Linear accelerators based on superconducting magnet technology use a large number of relatively weak superconducting quadrupoles. In this case an iron dominated quadrupole is the most cost effective solution. The field quality in this magnet is defined by iron poles; the magnet air gap is minimal as are coil ampere-turns. Nevertheless, it has long racetrack type coils, which must be rigid and fixed by a mechanical structure to provide the needed mechanical stability. The novel concept of using circular superconducting coils in such a quadrupole type is described, with a discussion of quadrupole parameters, and results of 3D magnetic designs. Variants of short and long sectional quadrupoles and multipoles are presented.

  10. Attosecond-magnetic-field-pulse generation by electronic currents in bichromatic circularly polarized UV laser fields

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2015-12-01

    Attosecond-magnetic-field-pulse generation is simulated from numerical solutions of time-dependent Schrödinger equations for oriented H2 +. Two schemes with high frequency co- and counter-rotating bichromatic ω2=2 ω1 circularly polarized UV laser pulses are investigated. Results show that comparing to single color processes, stronger induced localized magnetic fields B at the molecular center O (r =0 ) are obtained with attosecond duration. This is attributed to frequent recollision and to interference effects of two pathways in photoionization. The induced magnetic fields are shown to be sensitive to (i) the helicity of the combined laser pulses due to different recollision laser-induced electron trajectories and currents, and (ii) also the carrier envelope phases of the combined attosecond laser pulses. The sensitivity of recollision to bichromatic pulses thus allows one to control the induced magnetic-field-pulse generation.

  11. SEARCH FOR A MAGNETIC FIELD VIA CIRCULAR POLARIZATION IN THE WOLF-RAYET STAR EZ CMa

    SciTech Connect

    De la Chevrotiere, A.; St-Louis, N.; Moffat, A. F. J.; Collaboration: MiMeS Collaboration

    2013-02-20

    We report on the first deep, direct search for a magnetic field via the circular polarization of Zeeman splitting in a Wolf-Rayet (W-R) star. Using the highly efficient ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, we observed at three different epochs one of the best W-R candidates in the sky expected to harbor a magnetic field, the bright, highly variable WN4 star EZ CMa = WR6 = HD 50896. We looked for the characteristic circular polarization (Stokes V) pattern in strong emission lines that would arise as a consequence of a global, rotating magnetic field with a split monopole configuration. We also obtained nearly simultaneous linear polarization spectra (Stokes Q and U), which are dominated by electron scattering, most likely from a flattened wind with large-scale corotating structures. As the star rotates with a period of 3.766 days, our view of the wind changes, which in turn affects the value of the linear polarization in lines versus continuum at the {approx}0.2% level. Depending on the epoch of observation, our Stokes V data were affected by significant crosstalk from Stokes Q and U to V. We removed this spurious signal from the circular polarization data and experimented with various levels of spectral binning to increase the signal-to-noise ratio of our data. In the end, no magnetic field is unambiguously detected in EZ CMa. Assuming that the star is intrinsically magnetic and harbors a split monopole configuration, we find an upper limit of B {approx} 100 G for the intensity of its field in the line-forming regions of the stellar wind.

  12. Absorption Features in Spectra of Magnetized Neutron Stars

    SciTech Connect

    Suleimanov, V.; Hambaryan, V.; Neuhaeuser, R.; Potekhin, A. Y.; Pavlov, G. G.; Adelsberg, M. van; Werner, K.

    2011-09-21

    The X-ray spectra of some magnetized isolated neutron stars (NSs) show absorption features with equivalent widths (EWs) of 50-200 eV, whose nature is not yet well known.To explain the prominent absorption features in the soft X-ray spectra of the highly magnetized (B{approx}10{sup 14} G) X-ray dim isolated NSs (XDINSs), we theoretically investigate different NS local surface models, including naked condensed iron surfaces and partially ionized hydrogen model atmospheres, with semi-infinite and thin atmospheres above the condensed surface. We also developed a code for computing light curves and integral emergent spectra of magnetized neutron stars with various temperature and magnetic field distributions over the NS surface. We compare the general properties of the computed and observed light curves and integral spectra for XDINS RBS 1223 and conclude that the observations can be explained by a thin hydrogen atmosphere above the condensed iron surface, while the presence of a strong toroidal magnetic field component on the XDINS surface is unlikely.We suggest that the harmonically spaced absorption features in the soft X-ray spectrum of the central compact object (CCO) 1E 1207.4-5209 (hereafter 1E 1207) correspond to peaks in the energy dependence of the free-free opacity in a quantizing magnetic field, known as quantum oscillations. To explore observable properties of these quantum oscillations, we calculate models of hydrogen NS atmospheres with B{approx}10{sup 10}-10{sup 11} G(i.e., electron cyclotron energy E{sub c,e}{approx}0.1-1 keV) and T{sub eff} = 1-3 MK. Such conditions are thought to be typical for 1E 1207. We show that observable features at the electron cyclotron harmonics with EWs {approx_equal}100-200 eV can arise due to these quantum oscillations.

  13. Exploring 360 domain walls in ferromagnetic nanostructures using circular magnetic fields

    NASA Astrophysics Data System (ADS)

    Sarella, Anandakumar; Kaya, F. I.; Aidala, K. E.

    Ferromagnetic nanostructures can exhibit intriguing magnetic states, such as the metastable 360 domain wall (DW), in which two 180 DWs combine to form a nearly flux closed state in sufficiently thin structures. These composite structures have potential to maximize storage densities due to their minimal stray fields. We study a straightforward method to nucleate 360 DWs in nanorings, nanowires, using in-plane circular fields, as if from a current carrying wire passing through the substrate in close proximity to the nanostructures. Our simulations, using OOMMF, predict that the vortex state of a ring with appropriate geometry will reverse from CW to CCW through an intermediate state consisting of pairs of 360 DWs. We examine the dependence of the switching field and intermediate states on geometric properties such as the diameter, thickness, and width of the ring. Using the local circular field, we can also nucleate 360 DWs in nanowires, pinning the location of the DWs at notches spaced as close as 100 nm apart, suggesting high density storage. We are currently studying these structures experimentally using AFM/MFM. We generate the circular field by passing current through AFM tip and image the resulting magnetic states with MFM. NSF Grants No. DMR 1208042 and 1207924. Simulations were run on the Odyssey cluster, Research Computing Group at Harvard.

  14. Near-infrared Imaging Polarimetry of GGD 27: Circular Polarization and Magnetic Field Structures

    NASA Astrophysics Data System (ADS)

    Kwon, Jungmi; Tamura, Motohide; Hough, James H.; Nagata, Tetsuya; Kusakabe, Nobuhiko; Saito, Hiro

    2016-06-01

    Near-infrared imaging polarimetry in the J, H, and K s bands was carried out for GGD 27 in the dark cloud Lynds 291. Details of an infrared reflection nebula associated with the optical nebulosity GGD 27 and the infrared nebula GGD 27 IRS are presented. Aperture photometry of 1263 point-like sources, detected in all three bands, was used to classify them based on a color–color diagram, and the linear polarization of several hundred sources was determined, with the latter used to map the magnetic field structure around GGD 27. This field, around GGD 27 IRS, appears to be associated with the extended CO outflow of IRAS 18162–2048 however, there are partly distorted or bent components in the field. The Chandrasekhar–Fermi method gives an estimate of the magnetic field strength as ˜90 μG. A region associated with GGD 27 IRS is discovered to have a circular polarization in the range of ˜2%–11% in the K s band. The circular polarization has an asymmetric positive/negative pattern and extends out to ˜ 120″ or 1.0 pc. The circular and linear polarization patterns are explained as resulting from a combination of dense inner and fainter outer lobes, suggesting episodic outflow.

  15. Circular-cylindrical flux-rope analytical model for Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Nieves-Chinchilla, Teresa; Linton, Mark; Hidalgo, Miguel A.; Vourlidas, Angelos; Savani, Neel P.; Szabo, Adam; Farrugia, Charlie; Yu, Wenyuan

    2016-05-01

    We present an analytical model to describe magnetic flux-rope topologies. When these structures are observed embedded in Interplanetary Coronal Mass Ejections (ICMEs) with a depressed proton temperature, they are called Magnetic Clouds ( MCs). The model extends the circular-cylindrical concept of Hidalgo et al. (2000) by introducing a general form for the radial dependence of the current density. This generalization provides information on the force distribution inside the flux rope in addition to the usual parameters of MC geometrical information and orientation.The generalized model provides flexibility for implementation in 3D MHD simulations. Here, we evaluate its performance in the reconstruction of MCs in in-situ observations. Four Earth directed ICME events, observed by the Wind spacecraft, are used to validate the technique. The events are selected from the ICME Wind list with the magnetic obstacle boundaries chosen consistently with the magnetic fi eld and plasma in situ observations and with a new parameter (EPP, Electron Pitch angle distribution Parameter) which quantifies the bidirectionally of theplasma electrons. The goodness of the fit is evaluated with a single correlation parameter to enable comparative analysis of the events. In general, at first glance, the model fits the selected events very well. However, a detailed analysis of events with signatures of significant compression indicates the need to explore geometries other than the circular-cylindrical.

  16. A method for embedding circular force-free flux ropes in potential magnetic fields

    SciTech Connect

    Titov, V. S.; Török, T.; Mikic, Z.; Linker, J. A.

    2014-08-01

    We propose a method for constructing approximate force-free equilibria in pre-eruptive configurations in which a thin force-free flux rope is embedded into a locally bipolar-type potential magnetic field. The flux rope is assumed to have a circular-arc axis, a circular cross-section, and electric current that is either concentrated in a thin layer at the boundary of the rope or smoothly distributed across it with a maximum of the current density at the center. The entire solution is described in terms of the magnetic vector potential in order to facilitate the implementation of the method in numerical magnetohydrodynamic (MHD) codes that evolve the vector potential rather than the magnetic field itself. The parameters of the flux rope can be chosen so that its subsequent MHD relaxation under photospheric line-tied boundary conditions leads to nearly exact numerical equilibria. To show the capabilities of our method, we apply it to several cases with different ambient magnetic fields and internal flux-rope structures. These examples demonstrate that the proposed method is a useful tool for initializing data-driven simulations of solar eruptions.

  17. Classical Magnetic Dipole Moments for the Simulation of Vibrational Circular Dichroism by ab Initio Molecular Dynamics.

    PubMed

    Thomas, Martin; Kirchner, Barbara

    2016-02-01

    We present a new approach for calculating vibrational circular dichroism spectra by ab initio molecular dynamics. In the context of molecular dynamics, these spectra are given by the Fourier transform of the cross-correlation function of magnetic dipole moment and electric dipole moment. We obtain the magnetic dipole moment from the electric current density according to the classical definition. The electric current density is computed by solving a partial differential equation derived from the continuity equation and the condition that eddy currents should be absent. In combination with a radical Voronoi tessellation, this yields an individual magnetic dipole moment for each molecule in a bulk phase simulation. Using the chiral alcohol 2-butanol as an example, we show that experimental spectra are reproduced very well. Our approach requires knowing only the electron density in each simulation step, and it is not restricted to any particular electronic structure method. PMID:26771403

  18. Detection of magnetic circular dichroism on the two-nanometer scale

    NASA Astrophysics Data System (ADS)

    Schattschneider, Peter; Stöger-Pollach, Michael; Rubino, Stefano; Sperl, Matthias; Hurm, Christian; Zweck, Josef; Rusz, Ján

    2008-09-01

    Magnetic circular dichroism (MCD) is a standard technique for the study of magnetic properties of materials in synchrotron beamlines. We present here a scattering geometry in the transmission electron microscope through which MCD can be observed with unprecedented spatial resolution. A convergent electron beam is used to scan a cross sectional preparation of a Fe/Au multilayer sample. Differences in the energy-loss spectra induced by the magnetic moments of the Fe atoms can be resolved with a resolution of better than 2 nm. This is a breakthrough achievement when compared both to the previous energy-loss MCD resolution (200 nm) or the best x-ray MCD experiments (approximately 20 nm).

  19. X-ray magnetic circular dichroism on La2/3Ca1/3Mn0.97Fe0.03O3 thin films

    NASA Astrophysics Data System (ADS)

    Figueroa, Adriana I.; Campillo, Gloria E.; Baker, Alexander A.; Osorio, Jaime A.; Arnache, Oscar L.; van der Laan, Gerrit

    2015-11-01

    The element-selective technique of X-ray magnetic circular dichroism (XMCD) has been used to study the magnetic properties of La2/3Ca1/3Mn0.97Fe0.03O3 (LCMFO) thin films. XMCD measurements below the ferromagnetic ordering temperature at the Mn and Fe L2,3 absorption edges allow the determination of the contributions and relative orientations of the Mn and Fe magnetic moments. A reduction in the Mn L2,3 XMCD signal of the LCMFO sample compared to that for the parent La2/3Ca1/3MnO3 (LCMO) system reveals important modifications in the electronic and magnetic properties with the presence of Fe. The Fe L2,3 X-ray absorption (XAS) for the LCMFO film is characteristic of Fe3+, and the comparison with multiplet calculations shows that the Fe dopants occupy octahedral sites in the crystal, which is consistent with Fe3+ substituting Mn3+ in LCMO. The magnetic moments of Mn and Fe are found to align antiparallel, which suggests the presence of Mn-O-Fe superexchange coupling. This result is consistent with macroscopic magnetometry measurements on the LCMFO system, which show a decrease in saturation magnetization of LCMO with Fe doping.

  20. Simple Analytic Expressions for the Magnetic Field of a Circular Current Loop

    NASA Technical Reports Server (NTRS)

    Simpson, James C.; Lane, John E.; Immer, Christopher D.; Youngquist, Robert C.

    2001-01-01

    Analytic expressions for the magnetic induction (magnetic flux density, B) of a simple planar circular current loop have been published in Cartesian and cylindrical coordinates [1,2], and are also known implicitly in spherical coordinates [3]. In this paper, we present explicit analytic expressions for B and its spatial derivatives in Cartesian, cylindrical, and spherical coordinates for a filamentary current loop. These results were obtained with extensive use of Mathematica "TM" and are exact throughout all space outside of the conductor. The field expressions reduce to the well-known limiting cases and satisfy V · B = 0 and V x B = 0 outside the conductor. These results are general and applicable to any model using filamentary circular current loops. Solenoids of arbitrary size may be easily modeled by approximating the total magnetic induction as the sum of those for the individual loops. The inclusion of the spatial derivatives expands their utility to magnetohydrodynamics where the derivatives are required. The equations can be coded into any high-level programming language. It is necessary to numerically evaluate complete elliptic integrals of the first and second kind, but this capability is now available with most programming packages.

  1. Electronic studies of chrysene. Linear and magnetic circular dichroism and quantum chemical calculations

    SciTech Connect

    Spanget-Larsen, J. ); Waluk, J. ); Thulstrup, E.W. )

    1990-03-08

    The electronic transitions of chrysene are investigated by linear dichroism spectroscopy in stretched polyethylene and by magnetic circular dichroism spectroscopy, leading to the assignment of seven excited singlet states below 47,000 cm{sup {minus}1}. One of these has not previously been observed. The linear dichroism data, combined with previously published fluorescence polarization results, lead to precise determination of transition moment directions for five transitions. The experimental results are compared with theoretical predictions with the PPP, LCOAO, CNDO/S, and INDO/S quantum chemical models.

  2. Numerical characterization of a flexible circular coil for magnetic resonance imaging

    NASA Astrophysics Data System (ADS)

    Bautista, T.; Hernandez, R.; Solis-Najera, S. E.; Rodriguez, A. O.

    2012-10-01

    Numerical simulations of the magnetic field generated by a flexible surface coil were conducted to study its behavior for applications of animal models at 7 Tesla. This coil design is able to fully cover a volume of interest. The Finite Difference Method in Time Domain (FDTD) was used because of its ability to accurately model complex problems in electromagnetism. This particular coil design is best suited for regions of interests with a spherical shape, since B1 uniformity is not significantly attenuated as in the case of a circular-loop coil. It still remains to investigate the feasibility to actually construct a coil prototype.

  3. Uniform magnetic fields generated by circular current-carrying coils. [for spacecraft

    NASA Technical Reports Server (NTRS)

    Williams, V. L.; Cain, J. C.

    1975-01-01

    The study described was carried out to evaluate known systems of circular coils with a view toward their application on board the space probes Ranger 1, Ranger 2, and Explorer 10. Particular attention is given to a new method, developed during the investigation, for determining the constants of systems composed of 6 to 8 coils. Such systems were found to generate magnetic fields of very high uniformity. By using advanced computational techniques, it proved possible to evaluate the field uniformity of various systems without recourse to complex analytical methods. Means of evaluating the influence of coil dimensions on the uniformity of the field of any system are described.

  4. Optical and structural properties of plasma-treated Cordyceps bassiana spores as studied by circular dichroism, absorption, and fluorescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Geon Joon; Sim, Geon Bo; Choi, Eun Ha; Kwon, Young-Wan; Kim, Jun Young; Jang, Siun; Kim, Seong Hwan

    2015-01-01

    To understand the killing mechanism of fungal spores by plasma treatment, the optical, structural, and biological properties of the insect pathogenic fungus Cordyceps bassiana spores were studied. A nonthermal atmospheric-pressure plasma jet (APPJ) was used to treat the spores in aqueous solution. Optical emission spectra of the APPJ acquired in air indicated emission peaks corresponding to hydroxyl radicals and atomic oxygen. When the APPJ entered the aqueous solution, additional reactive species were derived from the interaction of plasma radicals with the aqueous solution. Fluorescence and absorption spectroscopy confirmed the generation of hydroxyl radicals and hydrogen peroxide in the plasma-activated water (PAW). Spore counting showed that plasma treatment significantly reduced spore viability. Absorption spectroscopy, circular dichroism (CD) spectroscopy, and agarose gel electrophoresis of the DNA extracted from plasma-treated spores showed a reduction in spore DNA content. The magnitude of the dip in the CD spectrum was lower in the plasma-treated spores than in the control, indicating that plasma treatment causes structural modifications and/or damage to cellular components. Tryptophan fluorescence intensity was lower in the plasma-treated spores than in the control, suggesting that plasma treatment modified cell wall proteins. Changes in spore viability and DNA content were attributed to structural modification of the cell wall by reactive species coming from the APPJ and the PAW. Our results provided evidence that the plasma radicals and the derived reactive species play critical roles in fungal spore inactivation.

  5. Optical and structural properties of plasma-treated Cordyceps bassiana spores as studied by circular dichroism, absorption, and fluorescence spectroscopy

    SciTech Connect

    Lee, Geon Joon Sim, Geon Bo; Choi, Eun Ha; Kim, Jun Young; Jang, Siun; Kim, Seong Hwan

    2015-01-14

    To understand the killing mechanism of fungal spores by plasma treatment, the optical, structural, and biological properties of the insect pathogenic fungus Cordyceps bassiana spores were studied. A nonthermal atmospheric-pressure plasma jet (APPJ) was used to treat the spores in aqueous solution. Optical emission spectra of the APPJ acquired in air indicated emission peaks corresponding to hydroxyl radicals and atomic oxygen. When the APPJ entered the aqueous solution, additional reactive species were derived from the interaction of plasma radicals with the aqueous solution. Fluorescence and absorption spectroscopy confirmed the generation of hydroxyl radicals and hydrogen peroxide in the plasma-activated water (PAW). Spore counting showed that plasma treatment significantly reduced spore viability. Absorption spectroscopy, circular dichroism (CD) spectroscopy, and agarose gel electrophoresis of the DNA extracted from plasma-treated spores showed a reduction in spore DNA content. The magnitude of the dip in the CD spectrum was lower in the plasma-treated spores than in the control, indicating that plasma treatment causes structural modifications and/or damage to cellular components. Tryptophan fluorescence intensity was lower in the plasma-treated spores than in the control, suggesting that plasma treatment modified cell wall proteins. Changes in spore viability and DNA content were attributed to structural modification of the cell wall by reactive species coming from the APPJ and the PAW. Our results provided evidence that the plasma radicals and the derived reactive species play critical roles in fungal spore inactivation.

  6. Interaction of a circularly polarised gravitational wave with a charged particle in a static magnetic background

    NASA Astrophysics Data System (ADS)

    Gangopadhyay, Sunandan; Saha, Anirban; Saha, Swarup

    2015-06-01

    Interaction of a charged particle in a static magnetic background, i.e., a Landau system with circularly polarised gravitational wave (GW) is studied quantum mechanically in the long wavelength and low velocity limit. We quantize the classical Hamiltonian following (Speliotopoulos in Phys Rev D 51:1701, 1995). The rotating polarization vectors of the circularly polarized GW are employed to form a unique directional triad which served as the coordinate axes. The Schrodinger equations for the system are cast in the form of a set of coupled linear differential equations. This system is solved by iterative technique. We compute the time-evolution of the position and momentum expectation values of the particle. The results show that the resonance behaviour obtained earlier (Macedo and Nelson in Astrophys J 362:584, 1990; Papadopoulos in Astron Astrophys 396:1045, 2002) by classical treatements of the system has a quantum analogue not only for the linearly polarized GW (Gangopadhyay and Saha in Mod Phys Lett A 27:1250192, 2012), but for circularly polarized GW as well.

  7. Circular Polarimetry: Diagnostic of Magnetic Fields, Atmospheric Aerosols and Biologic Activity

    NASA Astrophysics Data System (ADS)

    Yanamandra-Fisher, P. A.

    2013-12-01

    The overarching goals for the remote sensing and robotic exploration of planetary systems are: (1) understanding the formation of planetary systems and their diversity; and (2) search for habitability. Our solar system is a dynamic laboratory with unique linear and circular polarimetric signatures of planets, satellites, comets, asteroids, dust, etc.. The study of both linear and circular polarization of a given system, therefore, provides insight into its origin and physical properties. Specifically, linear and circular polarimetric signatures of the object arise from different physical processes. Additionally, spectral dependence of polarization is important to separate the macroscopic (bulk) properties of the scattering medium from the microscopic (particulate) properties of the scattering medium. Linear polarization of reflected light by various solar system objects provides insight into the scattering characteristics of atmospheric aerosols and hazes; and surficial properties of atmosphereless bodies. Measurements of linear limb polarization characterizes the variation of aerosol properties across the planetary disk. Many optically active materials are anisotropic and so their scattering properties differ with the object's principal axes (such as dichroic or birefringent materials) and are crystalline in structure instead of amorphous, eg., the presence of olivines and silicates in cometary dust and circumstellar disks; Titan, etc.). Ices (water and other species) are abundant in the system indicated in their near-infrared spectra. Gas giants form outside the frost line (where ices condense), and their satellites and ring systems exhibit signature of water ice; clathrates, non-ices (Si, C, Fe) in their NIR spectra and spectral dependence of linear polarization. Circular polarization is diagnostic of magnetic fields, atmospheric aerosols and biologic activity. Aurorae occur in response to changing local magnetic fields (Earth, Jupiter, Ganymede, etc.). Biologic

  8. Circular Rydberg States of the Hydrogen Atom in a Magnetic Field

    SciTech Connect

    Germann, T.C.; Herschbach, D.R. ); Dunn, M.; Watson, D.K. )

    1995-01-30

    Dimensional perturbation theory is used to study circular Rydberg states ([vert bar][ital m][vert bar]=[ital n][minus]1[much gt]1) and other large [vert bar][ital m][vert bar] states of the hydrogen atom in a uniform magnetic field. Because of a degeneracy between states of increased angular momentum and states of increased Cartesian dimensionality, the accuracy of the zeroth-order [ital D][r arrow][infinity] limit and a dimensional perturbation expansion improves significantly for states with larger [vert bar][ital m][vert bar]. In contrast to other approaches, this method is applicable to the entire range of magnetic field strengths. Energies and expectation values are presented as functions of the field strength.

  9. Interference of spin states in resonant photoemission induced by circularly polarized light from magnetized Gd

    SciTech Connect

    Mueller, N.; Khalil, T.; Pohl, M.; Uphues, T.; Heinzmann, U.; Polcik, M.; Rader, O.; Heigl, F.; Starke, K.; Fritzsche, S.; Kabachnik, N. M.

    2006-10-15

    We have observed the spin-state interference by measuring the photoelectron spin polarization in the resonant preedge 4d{yields}4f photoemission from magnetized Gd. The photoemission is induced by circularly polarized light which determines one preferential direction of electron spin orientation due to polarization transfer and spin-orbit interaction. Another direction perpendicular to the first one is determined by the target electron spin orientation connected with the target magnetization. We have measured the component of spin polarization perpendicular to those two directions which can only appear due to spin-state interference which implies coherence of the spin states produced by the two mechanisms of the photoelectron spin polarization.

  10. Spin-wave spectra of perpendicularly magnetized circular submicron dot arrays

    NASA Astrophysics Data System (ADS)

    Kakazei, G. N.; Wigen, P. E.; Guslienko, K. Yu.; Novosad, V.; Slavin, A. N.; Golub, V. O.; Lesnik, N. A.; Otani, Y.

    2004-07-01

    Dynamic microwave properties of arrays of circular Ni and Ni81Fe19 dots were studied by X-band ferromagnetic resonance (FMR) technique. All of the dots had the same radius 0.5μm, thickness 50-70nm, and were arranged into rectangular or square array with different interdot separations. In the case of perpendicular magnetization multiple (up to 8) sharp resonance peaks were observed below the main FMR peak, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra is given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account.

  11. Geometry effects on magnetization dynamics in circular cross-section wires

    SciTech Connect

    Sturma, M.; Toussaint, J.-C. E-mail: daria.gusakova@cea.fr; Gusakova, D. E-mail: daria.gusakova@cea.fr

    2015-06-28

    Three-dimensional magnetic memory design based on circular-cross section nanowires with modulated diameter is the emerging field of spintronics. The consequences of the mutual interaction between electron spins and local magnetic moments in such non-trivial geometries are still open to debate. This paper describes the theoretical study of domain wall dynamics within such wires subjected to spin polarized current. We used our home-made finite element software to characterize the variety of domain wall dynamical regimes observed for different constriction to wire diameter ratios d/D. Also, we studied how sizeable geometry irregularities modify the internal micromagnetic configuration and the electron spin spatial distribution in the system, the geometrical reasons underlying the additional contribution to the system's nonadiabaticity, and the specific domain wall width oscillations inherent to fully three-dimensional systems.

  12. Circular polarization dependent cyclotron resonance in large-area graphene in ultrahigh magnetic fields

    NASA Astrophysics Data System (ADS)

    Booshehri, L. G.; Mielke, C. H.; Rickel, D. G.; Crooker, S. A.; Zhang, Q.; Ren, L.; Hároz, E. H.; Rustagi, A.; Stanton, C. J.; Jin, Z.; Sun, Z.; Yan, Z.; Tour, J. M.; Kono, J.

    2012-05-01

    Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 μm, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular polarization dependent studies reveal strong p-type doping for as-grown graphene, and the dependence of the cyclotron resonance on radiation wavelength allows for a determination of the Fermi energy. Thermal annealing shifts the Fermi energy to near the Dirac point, resulting in the simultaneous appearance of hole and electron cyclotron resonance in the magnetic quantum limit, even though the sample is still p-type, due to graphene's linear dispersion and unique Landau level structure. These high-field studies therefore allow for a clear identification of cyclotron resonance features in large-area, low-mobility graphene samples.

  13. Fermionic condensate in a conical space with a circular boundary and magnetic flux

    SciTech Connect

    Bellucci, S.; Bezerra de Mello, E. R.; Saharian, A. A.

    2011-04-15

    The fermionic condensate is investigated in a (2+1)-dimensional conical spacetime in the presence of a circular boundary and a magnetic flux. It is assumed that on the boundary the fermionic field obeys the MIT bag boundary condition. For irregular modes, we consider a special case of boundary conditions at the cone apex, when the MIT bag boundary condition is imposed at a finite radius, which is then taken to zero. The fermionic condensate is a periodic function of the magnetic flux with the period equal to the flux quantum. For both exterior and interior regions, the fermionic condensate is decomposed into boundary-free and boundary-induced parts. Two integral representations are given for the boundary-free part for arbitrary values of the opening angle of the cone and magnetic flux. At distances from the boundary larger than the Compton wavelength of the fermion particle, the condensate decays exponentially, with the decay rate depending on the opening angle of the cone. If the ratio of the magnetic flux to the flux quantum is not a half-integer number for a massless field the boundary-free part in the fermionic condensate vanishes, whereas the boundary-induced part is negative. For half-integer values of the ratio of the magnetic flux to the flux quantum, the irregular mode gives a nonzero contribution to the fermionic condensate in the boundary-free conical space.

  14. Circular polarimetry reveals helical magnetic fields in the young stellar object HH 135-136.

    PubMed

    Chrysostomou, Antonio; Lucas, Philip W; Hough, James H

    2007-11-01

    Magnetic fields are believed to have a vital role in regulating and shaping the flow of material onto and away from protostars during their initial mass accretion phase. It is becoming increasingly accepted that bipolar outflows are generated and collimated as material is driven along magnetic field lines and centrifugally accelerated off a rotating accretion disk. However, the precise role of the magnetic field is poorly understood and evidence for its shape and structure has not been forthcoming. Here we report imaging circular polarimetry in the near-infrared and Monte Carlo modelling showing that the magnetic field along the bipolar outflow of the HH 135-136 young stellar object is helical. The field retains this shape for large distances along the outflow, so the field structure can also provide the necessary magnetic pressure for collimation of the outflow. This result lends further weight to the hypothesis--central to any theory of star formation--that the outflow is an important instrument for the removal of high-angular-momentum material from the accretion disk, thereby allowing the central protostar to increase its mass.

  15. Ab initio calculations of X-ray magnetic circular dichroism spectra within the projector augmented wave method: An implementation into the VASP code

    NASA Astrophysics Data System (ADS)

    Dixit, Anant; Alouani, M.

    2016-10-01

    X-ray absorption and X-ray magnetic circular dichroism (XMCD) are very powerful tools for probing the orbital and spin moments of each atomic species orbital of magnetic materials. In this work, we present the implementation of a module for computing the X-ray absorption and XMCD spectra into the VASP code. We provide a derivation of the absorption cross-section in the electric dipole approximation. The matrix elements, which make up the X-ray absorption cross-section for a given polarization of light, are then computed using either the momentum operator p or the position operator r, within the projector augmented wave method. The core electrons are described using the relativistic basis-set whereas for the valence electrons, the spin-orbit coupling is added perturbatively to the semi-relativistic Hamiltonian. We show that both the p and the r implementations lead to the same results. The results for the K-edge and L23-edges of bcc-iron are then computed and compared to experiment.

  16. X-ray magnetic-circular-dichroism study of Ni/Fe (001) multilayers

    SciTech Connect

    Lin, T.; Schwickert, M.M.; Tomaz, M.A.; Chen, H.; Harp, G.R.

    1999-06-01

    The structure and magnetic properties of Fe/Ni(001) multilayers are studied using x-ray diffraction, magneto-optical Kerr effect magnetometry, and x-ray magnetic circular dichroism. Multilayers are deposited with constant Fe layers (12 {Angstrom}) and wedged Ni layers (0{endash}30 {Angstrom}), repeated 20 times, to explore the magnetic moment and the structure dependence upon thickness of Ni (t{sub Ni}). Up to t{sub Ni}{approx}16 {Angstrom} (11 ML), both the Fe and the Ni have a bct structure, similar to the bulk structure of bcc Fe. The magnetic moments of Ni in the bct region are nearly constant at 0.85{mu}{sub B} for a Ni thickness t{sub Ni} in the range 3 {Angstrom}{lt}t{sub Ni}{lt}16 {Angstrom}. This represents a significant enhancement over the moment in bulk fcc Ni (0.59{mu}B). The Fe/Ni multilayer undergoes a crystalline phase transition between 16 {Angstrom}{lt}t{sub Ni}{lt}23 {Angstrom}, beyond which both the Fe and Ni have an fct structure. In the fct region, the Ni magnetic moment is close to its bulk value and the Fe magnetic moment drops to 1.5{mu}{sub B}, which is {approximately}70{percent} of its bulk value. The crystalline phase transition is also accompanied by a rotation of the magnetic easy axis by 45{degree} in the plane of the film. {copyright} {ital 1999} {ital The American Physical Society}

  17. Magnetic and structural properties of Fe/Pd multilayers studied by magnetic x-ray dichroism and x-ray absorption spectroscopy

    SciTech Connect

    Mini, S.M. |; Fullerton, E.E.; Sowers, C.H.; Fontaine, A.; Pizzini, S.; Bommannavar, A.S.; Traverse, A.; Baudelet, F.

    1994-12-01

    The results of magnetic circular x-ray dichroism (MCXD) measurements and extended x-ray absorption fine structure measurements (EXAFS) of the Fe K-edges of textured Fe(110)/Pd(111) multilayers are reported. The EXAFS results indicates that the iron in the system goes from bcc to a more densely packed system as the thickness of the iron layer is decreased. The magnetic properties were measured by SQUID magnetometry from 5-350 K. For all the samples, the saturation magnetization was significantly enhanced over the bulk values indicating the interface Pd atoms are polarized by the Fe layer. The enhancement corresponds to a moment of {approx}2.5{mu}{sub B} per interface Pd atom.

  18. Resonant Absorption of Axisymmetric Modes in Twisted Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    Giagkiozis, I.; Goossens, M.; Verth, G.; Fedun, V.; Van Doorsselaere, T.

    2016-06-01

    It has been shown recently that magnetic twist and axisymmetric MHD modes are ubiquitous in the solar atmosphere, and therefore the study of resonant absorption for these modes has become a pressing issue because it can have important consequences for heating magnetic flux tubes in the solar atmosphere and the observed damping. In this investigation, for the first time, we calculate the damping rate for axisymmetric MHD waves in weakly twisted magnetic flux tubes. Our aim is to investigate the impact of resonant damping of these modes for solar atmospheric conditions. This analytical study is based on an idealized configuration of a straight magnetic flux tube with a weak magnetic twist inside as well as outside the tube. By implementing the conservation laws derived by Sakurai et al. and the analytic solutions for weakly twisted flux tubes obtained recently by Giagkiozis et al. we derive a dispersion relation for resonantly damped axisymmetric modes in the spectrum of the Alfvén continuum. We also obtain an insightful analytical expression for the damping rate in the long wavelength limit. Furthermore, it is shown that both the longitudinal magnetic field and the density, which are allowed to vary continuously in the inhomogeneous layer, have a significant impact on the damping time. Given the conditions in the solar atmosphere, resonantly damped axisymmetric modes are highly likely to be ubiquitous and play an important role in energy dissipation. We also suggest that, given the character of these waves, it is likely that they have already been observed in the guise of Alfvén waves.

  19. Quasi-static magnetic measurements to predict specific absorption rates in magnetic fluid hyperthermia experiments

    NASA Astrophysics Data System (ADS)

    Coral, D. F.; Mendoza Zélis, P.; de Sousa, M. E.; Muraca, D.; Lassalle, V.; Nicolás, P.; Ferreira, M. L.; Fernández van Raap, M. B.

    2014-01-01

    In this work, the issue on whether dynamic magnetic properties of polydispersed magnetic colloids modeled using physical magnitudes derived from quasi-static magnetic measurement can be extrapolated to analyze specific absorption rate data acquired at high amplitudes and frequencies of excitation fields is addressed. To this end, we have analyzed two colloids of magnetite nanoparticles coated with oleic acid and chitosan in water displaying, under a radiofrequency field, high and low specific heat power release. Both colloids are alike in terms of liquid carrier, surfactant and magnetic phase composition but differ on the nanoparticle structuring. The colloid displaying low specific dissipation consists of spaced magnetic nanoparticles of mean size around 4.8 nm inside a large chitosan particle of 52.5 nm. The one displaying high specific dissipation consists of clusters of magnetic nanoparticles of mean size around 9.7 nm inside a chitosan particle of 48.6 nm. The experimental evaluation of Néel and Brown relaxation times (˜10-10 s and 10-4 s, respectively) indicate that the nanoparticles in both colloids magnetically relax by Néel mechanism. The isothermal magnetization curves analysis for this mechanism show that the magnetic nanoparticles behave in the interacting superparamagnetic regime. The specific absorption rates were determined calorimetrically at 260 kHz and up to 52 kA/m and were well modeled within linear response theory using the anisotropy density energy retrieved from quasi-static magnetic measurement, validating their use to predict heating ability of a given polydispersed particle suspension. Our findings provide new insight in the validity of quasi-static magnetic characterization to analyze the high frequency behavior of polydispersed colloids within the framework of the linear response and Wohlfarth theories and indicate that dipolar interactions play a key role being their strength larger for the colloid displaying higher dissipation, i

  20. Dust Particle Alignment in the Solar Magnetic Field: a Possible Cause of the Cometary Circular Polarization

    NASA Astrophysics Data System (ADS)

    Kolokolova, L.; Koenders, C.; Rosenbush, V.; Kiselev, N.; Ivanova, A.; Afanasiev, V.

    2015-12-01

    Circular polarization (CP) produced by scattering of sunlight on cometary dust has been observed in 11 comets, and showed the values from 0.01% to 0.8%. CP of both signs was observed, although negative (left-handed) CP dominates. Recent observations of several comets using SCORPIO-2 focal reducer at the 6-m BTA telescope of the Special Astrophysical Observatory (Russia) allowed producing maps of CP in the comet continuum filter at 684 nm and red wide-band filter. A gradual increase of the CP with the nucleocentric distance was usually observed. The most plausible reason why the light scattered by cometary dust becomes circularly polarized is alignment of the dust particles in the solar magnetic field. However, in-situ data for comet Halley, indicated that the solar magnetic field could not penetrate deep into the coma, limited by the diamagnetic cavity, and, thus, could not be responsible for the CP observed closer than ~4000 km from the nucleus. Advanced theoretical studies of interaction of the solar magnetic field with cometary ions led to reconsidering the diamagnetic cavity boundary - it is defined by the cometary ionopause, at which a balance is achieved between the magnetic pressure in the magnetic pile up region and the neutral friction force. The nucleocentric distance where this balance is achieved depends on the comet characteristics, increasing with the increase of the gas production rate, and local solar wind conditions, approximatively given by the comet location, specifically, its heliocentric distance. The size of diamagnetic cavity was calculated for the conditions of our CP observations. We found that it could be as small as dozens (comets 73P, 8P, 290P) or hundreds (comets Q4 NEAT, K1 PanSTARRS, Tago-Sato-Kosaka) kilometers. Thus, non-zero CP close to the nucleus can be easily explained by the interaction of the dust particles with the solar magnetic field. This mechanism also explains the observed increase in CP with the distance from the

  1. X-ray magnetic circular dichroism and reflection anisotropy spectroscopy Kerr effect studies of capped magnetic nanowires

    SciTech Connect

    Cunniffe, J. P.; McNally, D.E.; Liberati, M.; Arenholz, E.; McGuinness, C.; McGilp, J. F.

    2010-03-02

    Aligned Co wires grown on Pt(997) under ultra-high vacuum conditions have been capped successfully by the epitaxial growth of Au monolayers (ML) at room temperature. The samples were kept under vacuum except when transferring between apparatus or when making some of the measurements. No degradation of the Co wires was detected during the measurements. The magneto-optic response of the system was measured using X-ray magnetic circular dichroism (XMCD) at the Co L{sub 2,3} edge and reflection anisotropy spectroscopy (RAS) at near normal incidence, which is sensitive to the normal component of the out-of-plane magnetization via the Kerr effect (MOKE). Capping the wires significantly impacts their magnetic properties. Comparison of the magneto-optic response of the system at X-ray and optical energies reveals small differences that are attributed to the induced moment in the Pt substrate and Au capping layer not picked up by the element specific XMCD measurements. The sensitivity of RAS-MOKE is sufficient to allow the determination of the easy axis direction of the capped wires to within a few degrees. The results for a 6-atom-wide Co wire sample, capped with 6 ML of Au, are consistent with the capped wires possessing perpendicular magnetization.

  2. Perpendicular magnetic anisotropy at the interface between ultrathin Fe film and MgO studied by angular-dependent x-ray magnetic circular dichroism

    SciTech Connect

    Okabayashi, J.; Koo, J. W.; Mitani, S.; Sukegawa, H.; Takagi, Y.; Yokoyama, T.

    2014-09-22

    Interface perpendicular magnetic anisotropy (PMA) in ultrathin Fe/MgO (001) has been investigated using angular-dependent x-ray magnetic circular dichroism (XMCD). We found that anisotropic orbital magnetic moments deduced from the analysis of XMCD contribute to the large PMA energies, whose values depend on the annealing temperature. The large PMA energies determined from magnetization measurements are related to those estimated from the XMCD and the anisotropic orbital magnetic moments through the spin-orbit interaction. The enhancement of anisotropic orbital magnetic moments can be explained mainly by the hybridization between the Fe 3d{sub z}{sup 2} and O 2p{sub z} states.

  3. Magnetic anisotropy in Ta/CoFeB/MgO investigated by x-ray magnetic circular dichroism and first-principles calculation

    SciTech Connect

    Kanai, Shun; Tsujikawa, Masahito; Shirai, Masafumi; Miura, Yoshio; Matsukura, Fumihiro Ohno, Hideo

    2014-12-01

    We study the spin and orbital magnetic moments in Ta/Co{sub 0.4}Fe{sub 0.4}B{sub 0.2}/MgO by x-ray magnetic circular dichroism measurements as well as first-principles calculations, in order to clarify the origin of the perpendicular magnetic anisotropy. Both experimental and theoretical results show that orbital magnetic moment of Fe is more anisotropic than that of Co with respect to the magnetization direction. The anisotropy is larger for thinner CoFeB, indicating that Fe atoms at the interface with MgO contribute more than Co to the observed perpendicular magnetic anisotropy.

  4. Polarization measurement and vertical aperture optimization for obtaining circularly polarized bend-magnet radiation

    SciTech Connect

    Kortright, J.B.; Rice, M.; Hussain, Z.

    1995-10-01

    Using multilayer linear polarizers, we have studied the polarization state of radiation from bend magnet beamline 9.3.2 at Advanced Light Source as function of vertical oping angle at photon energies 367 and 722 eV. Both a fine slit and a coarse semi-aperture were stepped across the beam to accept different parts of the vertical radiation fan. Polarimetry yields the degree of linear polarization directly and the degree of circular polarization indirectly assuming an immeasurably small amount of unpolarized radiation based on close agreement of theory and experiment for linear polarization. Results are in good agreement with theoretical calculations, with departures from theory owing to uncertainty in effective aperture of the measured beam. The narrow 0.037 mrad aperture on the orbit plane transmits a beam whose degree of linear polarization exceeds 0.99 at these energies. The wide semi-aperture blocking the beam from above and below transmits a beam with a max figure of merit, given by the square root of flux times degree of circular polarization, when the aperture edge is on the orbit plane thus blocking only half of the total available flux.

  5. Microwave absorption in nanocomposite material of magnetically functionalized carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Labunov, V. A.; Danilyuk, A. L.; Prudnikava, A. L.; Komissarov, I.; Shulitski, B. G.; Speisser, C.; Antoni, F.; Le Normand, F.; Prischepa, S. L.

    2012-07-01

    The interaction of electromagnetic radiation in X and Ka bands with magnetic nanocomposite of disordered carbon nanotubes arrays has been investigated both experimentally and theoretically. Samples were synthesized on the quartz reactor walls by decomposition of ferrocene and xylene which provided random intercalation of iron phase nanoparticles in carbon nanotube array. The exhaustive characterization of the samples by means of the scanning electron microscopy, Raman spectroscopy, and x-ray photoemission spectroscopy was performed. It was found that the absorption of the electromagnetic wave monotonically increases with the frequency. To describe these experimental data, we extended the Bruggeman effective medium theory to a more complex case of a magnetic nanocomposite with randomly distributed spherical ferromagnetic nanoparticles in a conducting medium. The essential feature of the developed model is the consideration of the complex nature of the studied material. In particular, such important parameters as magnetic and dielectric properties of both the carbon nanotube medium and the nanoparticles, the volume concentration and the dimensions of the nanoparticles, the wave impedance of the resistive-capacitive shells of the conductive nanoparticles are explicitly taken into account in our model. Moreover, analysing the experimental results, we were able to obtain the frequency dependencies of permittivity and permeability of the studied nanocomposite.

  6. Zeeman Splitting of Ferromagnetic GaMnAs on InP Observed by Magnetic Circular Dichroism in Reflection Mode

    NASA Astrophysics Data System (ADS)

    Tanaka, H.; Bsatee, M.; Jadwisienczak, W. M.

    2016-08-01

    Systematic investigations of Ga1- x Mn x As grown on InP with different Mn concentrations have been conducted using magnetic circular dichroism (MCD) in reflection mode. The MCD spectrum of Ga0.97Mn0.03As/InP was decomposed into two dispersion curves originating from E 1 and E 1 + Δ1 optical transitions using the energy derivative of a Gaussian function. The Zeeman splitting energy E 1 at the L critical point (0.6 meV) of ferromagnetic Ga0.97Mn0.03As/InP was estimated using a rigid band shift model. Based on the relationship between E 1 and E 0 (Γ critical point) observed in Cd1- x Mn x Te dilute magnetic semiconductor (DMS), the Zeeman splitting energy E 1 (9.6 meV) of ferromagnetic Ga1- x Mn x As/InP was calculated. In addition, it was established that the peaks in the MCD spectra at L critical points shift toward the lower energy side as the Mn concentration is increased, and the observed shift saturates for Mn content of x = 0.001. Furthermore, the measured absorption spectra for Ga1- x Mn x As/InP did not show noticeable peak shifts with increasing Mn content. This suggests that the s, p- d exchange interaction induced in Ga1- x Mn x As/InP has localized nature due to the presence of a Mn rigid sphere of influence.

  7. Von Zeipel's theorem for a magnetized circular flow around a compact object

    NASA Astrophysics Data System (ADS)

    Zanotti, O.; Pugliese, D.

    2015-04-01

    We analyze a class of physical properties, forming the content of the so-called von Zeipel theorem, which characterizes stationary, axisymmetric, non-selfgravitating perfect fluids in circular motion in the gravitational field of a compact object. We consider the extension of the theorem to the magnetohydrodynamic regime, under the assumption of an infinitely conductive fluid, both in the Newtonian and in the relativistic framework. When the magnetic field is toroidal, the conditions required by the theorem are equivalent to integrability conditions, as it is the case for purely hydrodynamic flows. When the magnetic field is poloidal, the analysis for the relativistic regime is substantially different with respect to the Newtonian case and additional constraints, in the form of PDEs, must be imposed on the magnetic field in order to guarantee that the angular velocity depends only on the specific angular momentum . In order to deduce such physical constraints, it is crucial to adopt special coordinates, which are adapted to the surfaces. The physical significance of these results is briefly discussed.

  8. High Field Magnetic Circular Dichroism in Ferromagnetic InMnSb and InMnAs

    NASA Astrophysics Data System (ADS)

    Meeker, M. A.; Magill, B. A.; Khodaparast, G. A.; Saha, D.; Stanton, C. J.; McGill, S.; Wessels, B. W.

    An understanding of the fundamental interactions in narrow gap ferromagnetic semiconductors such as InMnAs and InMnSb has been developed primarily from static magnetization and electrical transport measurements. In this study, to provide a better understanding of the coupling of the Mn impurities to the conduction and valence bands through the sp-d exchange interactions, we have performed magnetic circular dichroism measurements (MCD) on MOVPE grown InMnAs and InMnSb. In our samples, the Mn content varies from 2% to 10.7% and all the samples have Curie temperatures above 300 K. The samples were photo-excited using a Quartz Tungsten Halogen lamp with energies ranging between 0.92-1.45 eV, and in magnetic fields up to 31 T. The temperatures ranged from 15-190 K. Comparison of the observed MCD with theoretical calculations provides a direct method to probe the band structure including the temperature dependence of the spin-orbit split-off bandgap and g-factors, as well as a means to estimate the sp-d coupling constants. Supported by the AFOSR through grant FA9550-14-1-0376, NSF-Career Award DMR-0846834 , NSF-DMR-60035274 , NSF-DMR-1305666, NSF MRI program (DMR-1229217).

  9. Magnetic circular dichroism spectroscopy of N-confused porphyrin and its ionized forms.

    PubMed

    Ziegler, Christopher J; Erickson, Nathan R; Dahlby, Michael R; Dalby, Michael R; Nemykin, Victor N

    2013-11-14

    N-Confused porphyrin (NCP) and its externally methylated variant (MeNCP) were investigated using UV-vis and magnetic circular dichrosim (MCD) spectroscopies. In addition to evaluating the spectroscopy of the neutral compounds, the acid/base chemistry of these macrocycles was examined by the same methods. NCP exhibits two tautomeric states depending on the polarity of the solvent, and their protonation/deprotonation chemistries also differ depending on solvent polarity. DFT and TDDFT calculations were employed to evaluate the observed spectroscopic changes. Using both experimental and calculated results, we were able to determine the sites of protonation/deprotonation for both tautomeric forms of NCP. Inspection of the MCD Faraday B terms for all of the macrocycles presented in this report showed that the ΔHOMO > ΔLUMO condition is maintained in all cases, and these observations were in good agreement with the DFT calculations. PMID:24131398

  10. Optically detected electron paramagnetic resonance by microwave modulated magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Börger, Birgit; Bingham, Stephen J.; Gutschank, Jörg; Schweika, Marc Oliver; Suter, Dieter; Thomson, Andrew J.

    1999-11-01

    Electron paramagnetic resonance (EPR) can be detected optically, with a laser beam propagating perpendicular to the static magnetic field. As in conventional EPR, excitation uses a resonant microwave field. The detection process can be interpreted as coherent Raman scattering or as a modulation of the laser beam by the circular dichroism of the sample oscillating at the microwave frequency. The latter model suggests that the signal should show the same dependence on the optical wavelength as the MCD signal. We check this for two different samples [cytochrome c-551, a metalloprotein, and ruby (Cr3+:Al2O3)]. In both cases, the observed wavelength dependence is almost identical to that of the MCD signal. A quantitative estimate of the amplitude of the optically detected EPR signal from the MCD also shows good agreement with the experimental results.

  11. Magnetic circular dichroism spectroscopy of N-confused porphyrin and its ionized forms.

    PubMed

    Ziegler, Christopher J; Erickson, Nathan R; Dahlby, Michael R; Dalby, Michael R; Nemykin, Victor N

    2013-11-14

    N-Confused porphyrin (NCP) and its externally methylated variant (MeNCP) were investigated using UV-vis and magnetic circular dichrosim (MCD) spectroscopies. In addition to evaluating the spectroscopy of the neutral compounds, the acid/base chemistry of these macrocycles was examined by the same methods. NCP exhibits two tautomeric states depending on the polarity of the solvent, and their protonation/deprotonation chemistries also differ depending on solvent polarity. DFT and TDDFT calculations were employed to evaluate the observed spectroscopic changes. Using both experimental and calculated results, we were able to determine the sites of protonation/deprotonation for both tautomeric forms of NCP. Inspection of the MCD Faraday B terms for all of the macrocycles presented in this report showed that the ΔHOMO > ΔLUMO condition is maintained in all cases, and these observations were in good agreement with the DFT calculations.

  12. Pitch angle scattering of an energetic magnetized particle by a circularly polarized electromagnetic wave

    SciTech Connect

    Bellan, P. M.

    2013-04-15

    The interaction between a circularly polarized wave and an energetic gyrating particle is described using a relativistic pseudo-potential that is a function of the frequency mismatch. Analysis of the pseudo-potential provides a means for interpreting numerical results. The pseudo-potential profile depends on the initial mismatch, the normalized wave amplitude, and the initial angle between the wave magnetic field and the particle perpendicular velocity. For zero initial mismatch, the pseudo-potential consists of only one valley, but for finite mismatch, there can be two valleys separated by a hill. A large pitch angle scattering of the energetic electron can occur in the two-valley situation but fast scattering can also occur in a single valley. Examples relevant to magnetospheric whistler waves show that the energetic electron pitch angle can be deflected 5 Degree-Sign towards the loss cone when transiting a 10 ms long coherent wave packet having realistic parameters.

  13. Suppressed Magnetic Circular Dichroism and Valley-Selective Magnetoabsorption due to the Effective Mass Anisotropy in Bismuth.

    PubMed

    de Visser, Pieter J; Levallois, Julien; Tran, Michaël K; Poumirol, Jean-Marie; Nedoliuk, Ievgeniia O; Teyssier, Jérémie; Uher, Ctirad; van der Marel, Dirk; Kuzmenko, Alexey B

    2016-07-01

    We measure the far-infrared reflectivity and Kerr angle spectra on a high-quality crystal of pure semimetallic bismuth as a function of magnetic field, from which we extract the conductivity for left- and right-handed circular polarizations. The high spectral resolution allows us to separate the intraband Landau level transitions for electrons and holes. The hole transition exhibits 100% magnetic circular dichroism; it appears only for one polarization as expected for a circular cyclotron orbit. However, the dichroism for electron transitions is reduced to only 13±1%, which is quantitatively explained by the large effective mass anisotropy of the electron pockets of the Fermi surface. This observation is a signature of the mismatch between the metric experienced by the photons and the electrons. It allows for a contactless measurement of the effective mass anisotropy and provides a direction towards valley polarized magnetooptical pumping with elliptically polarized light. PMID:27419590

  14. {sup 57}Fe Moessbauer and x-ray magnetic circular dichroism study of magnetic compensation of the rare-earth sublattice in Nd{sub 2-x}Ho{sub x}Fe{sub 14}B compounds

    SciTech Connect

    Chaboy, J.; Piquer, C.; Plugaru, N.; Bartolome, F.; Laguna-Marco, M. A.

    2007-10-01

    We present here a study of the magnetic properties of the Nd{sub 2-x}Ho{sub x}Fe{sub 14}B series. The macroscopic properties of these compounds evolve continuously from those of Nd{sub 2}Fe{sub 14}B to those of Ho{sub 2}Fe{sub 14}B as Ho gradually replaces Nd. The system shows a compensation of the rare-earth sublattice magnetization for a critical concentration, x{sub c}=0.55, that is reflected into the anomalous behavior of both macroscopic and microscopic magnetic probes. The combined analysis of magnetization, {sup 57}Fe Moessbauer spectroscopy and Fe K-edge x-ray magnetic circular dichroism (XMCD) measurements suggests that the origin of the anomalous magnetic behavior found at x{sub c}=0.55 is mainly due to the Ho sublattice. Moreover, the analysis of the Fe K-edge XMCD signals reveal the presence of a rare-earth contribution, reflecting the coupling of the rare-earth and Fe magnetic moments, which can lead to the possibility of disentangling the magnetic behavior of both Fe and R atoms using a single absorption edge.

  15. Electron holography study of the temperature variation of the magnetic order parameter within circularly chained nickel nanoparticle rings

    SciTech Connect

    Sugawara, Akira; Fukunaga, Kei-ichi; Scheinfein, M. R.; Kobayashi, H.; Kitagawa, H.; Tonomura, A.

    2007-12-24

    The magnetic structure within circular chains composed of 30-nm-diameter, polymer-coated nickel particles was studied by electron holography. The magnetic flux closure due to dipolar coupling was confirmed at zero external magnetic field. Its long-range order parameter was determined from the magnitude of the electron phase shift, and it was found to decrease more rapidly than that of bulk nickel as a function of temperature. The results of Monte Carlo simulations indicated that the temperature variation of the order-parameter was explained in terms of weakened dipolar coupling field ascribed to the decay of the bulk magnetization and enhanced thermal fluctuations.

  16. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    DOE PAGES

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D. A.; Heiman, D.

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  17. Control of transmission of right circularly polarized laser light in overdense plasma by applied magnetic field pulses.

    PubMed

    Ma, Guangjin; Yu, Wei; Yu, M Y; Luan, Shixia; Wu, Dong

    2016-05-01

    The effect of a transient magnetic field on right-hand circularly polarized (RHCP) laser light propagation in overcritical-density plasma is investigated. When the electron gyrofrequency is larger than the wave frequency, RHCP light can propagate along the external magnetic field in an overcritical density plasma without resonance or cutoff. However, when the magnetic field falls to below the cyclotron resonance point, the propagating laser pulse will be truncated and the local plasma electrons resonantly heated. Particle-in-cell simulation shows that when applied to a thin slab, the process can produce intense two-cycle light pulses as well as long-lasting self-magnetic fields. PMID:27300997

  18. Control of transmission of right circularly polarized laser light in overdense plasma by applied magnetic field pulses

    NASA Astrophysics Data System (ADS)

    Ma, Guangjin; Yu, Wei; Yu, M. Y.; Luan, Shixia; Wu, Dong

    2016-05-01

    The effect of a transient magnetic field on right-hand circularly polarized (RHCP) laser light propagation in overcritical-density plasma is investigated. When the electron gyrofrequency is larger than the wave frequency, RHCP light can propagate along the external magnetic field in an overcritical density plasma without resonance or cutoff. However, when the magnetic field falls to below the cyclotron resonance point, the propagating laser pulse will be truncated and the local plasma electrons resonantly heated. Particle-in-cell simulation shows that when applied to a thin slab, the process can produce intense two-cycle light pulses as well as long-lasting self-magnetic fields.

  19. Magnetic resonance microwave absorption imaging: Feasibility of signal detection

    PubMed Central

    Xie, Bin; Weaver, John B.; Meaney, Paul M.; Paulsen, Keith D.

    2009-01-01

    Purpose: Magnetic resonance (MR) technique was used to detect small displacements induced by localized absorption of pulsed 434 MHz microwave power as a potential method for tumor detection. Methods: Phase contrast subtraction was used to separate the phase change due to motion from thermoelastic expansion from other contributions to phase variation such as the bulk temperature rise of the medium and phase offsets from the MR scanner itself. A simple set of experiments was performed where the motion was constrained to be one dimensional which provided controls on the data acquisition and motion extraction procedures. Specifically, the MR-detected motion signal was isolated by altering the direction of the microwave-induced motion and sampling the response with motion encoding gradients in all three directions when the microwave power was turned on and turned off. Results: Successful signal detection, as evidenced by the recording of a systematic alternating (zigzag) phase pattern, occurred only when the motion encoding was in parallel with either the vertical or horizontal direction of the microwave-induced motion on both 10 and 4 mm spatial scales. Conclusions: These results demonstrate, for the first time, that motion associated with thermoelastic expansion from the absorption of pulsed microwave power can be detected with MR. PMID:19994529

  20. Detection of electron magnetic circular dichroism signals under zone axial diffraction geometry.

    PubMed

    Song, Dongsheng; Rusz, Jan; Cai, Jianwang; Zhu, Jing

    2016-10-01

    EMCD (electron magnetic circular dichroism) technique provides us a new opportunity to explore magnetic properties in the transmission electron microscope. However, specific diffraction geometry is the major limitation. Only the two-beam and three-beam case are demonstrated in the experiments until now. Here, we present the more general case of zone axial (ZA) diffraction geometry through which the EMCD signals can be detected even with the very strong sensitivity to dynamical diffraction conditions. Our detailed calculations and well-controlled diffraction conditions lead to experiments in agreement with theory. The effect of dynamical diffraction conditions on EMCD signals are discussed both in theory and experiments. Moreover, with the detailed analysis of dynamical diffraction effects, we experimentally obtain the separate EMCD signals for each crystallographic site in Y3Fe5O12, which is also applicable for other materials and cannot be achieved by site-specific EMCD and XMCD technique directly. Our work extends application of more general diffraction geometries and will further promote the development of EMCD technique. PMID:27448200

  1. Beamline 9.3.2 - a high-resolution, bend-magnet beamline with circular polarization capability

    SciTech Connect

    Moler, E.J.; Hussain, Z.; Howells, M.R.

    1997-04-01

    Beamline 9.3.2 is a high resolution, SGM beamline on an ALS bending magnet with access to photon energies from 30-1500 eV. Features include circular polarization capability, a rotating chamber platform that allows switching between experiments without breaking vacuum, an active feedback system that keeps the beam centered on the entrance slit of the monochromator, and a bendable refocusing mirror. The beamline optics consist of horizontally and vertically focussing mirrors, a Spherical Grating Monochromator (SGM) with movable entrance and exit slits, and a bendable refocussing mirror. In addition, a movable aperature has been installed just upstream of the vertically focussing mirror which can select the x-rays above or below the plane of the synchrotron storage ring, allowing the user to select circularly or linearly polarized light. Circularly polarized x-rays are used to study the magnetic properties of materials. Beamline 9.3.2 can supply left and right circularly polarized x-rays by a computer controlled aperture which may be placed above or below the plane of the synchrotron storage ring. The degree of linear and circular polarization has been measured and calibrated.

  2. Parametric distortion of the optical absorption edge of a magnetic semiconductor by a strong laser field

    SciTech Connect

    Nunes, O.A.C.

    1985-09-15

    The influence of a strong laser field on the optical absorption edge of a direct-gap magnetic semiconductor is considered. It is shown that as the strong laser intensity increases the absorption coefficient is modified so as to give rise to an absorption tail below the free-field forbidden gap. An application is made for the case of the EuO.

  3. Magnetic circular dichroism spectroscopic characterization of the NOS-like protein from Geobacillus stearothermophilus (gsNOS).

    PubMed

    Kinloch, Ryan D; Sono, Masanori; Sudhamsu, Jawahar; Crane, Brian R; Dawson, John H

    2010-03-01

    Nitric oxide synthase (NOS) catalyzes the NADPH- and O(2)-dependent oxidation of l-arginine (l-Arg) to nitric oxide (NO) and citrulline via an N(G)-hydroxy-l-arginine (NHA) intermediate. Mammalian NOSs have been studied quite extensively; other eukaryotes and some prokaryotes appear to express NOS-like proteins comparable to the oxygenase domain of mammalian NOSs. In this study, a recombinant NOS-like protein from the thermostable bacterium Geobacillus stearothermophilus (gsNOS) has been characterized using magnetic circular dichroism (MCD) and UV-Vis absorption spectroscopic techniques. Spectral comparisons of ligand complexes (with O(2), NO and CO) of substrate-bound (l-Arg or NHA) gsNOS, including the key oxyferrous complex studied at -50 degrees C in cryogenic mixed solvents, with analogous mammalian NOS complexes indicate overall spectroscopic similarities between gsNOS and mammalian NOSs. However, more detailed spectral comparisons reflect subtle structural differences between gsNOS and mammalian NOSs. This may be due to an incomplete tetrahydrobiopterin (BH(4))-binding site and low BH(4)-binding affinity, which may become even lower in the presence of cryosolvent in gsNOS. Although BH(4)-binding may be altered, gsNOS appears to require the pterin for NO production since formation of the stable ferric-NO product complex was only observed when excess BH(4) (>150muM) over gsNOS was present upon single turnover reaction in which O(2) was bubbled into dithionite-reduced NHA-bound protein solution at -35 degrees C or -50 degrees C. PMID:20110129

  4. Indication of intrinsic room-temperature ferromagnetism in Ti1-xCoxO2-δ thin film: An x-ray magnetic circular dichroism study

    NASA Astrophysics Data System (ADS)

    Mamiya, K.; Koide, T.; Fujimori, A.; Tokano, H.; Manaka, H.; Tanaka, A.; Toyosaki, H.; Fukumura, T.; Kawasaki, M.

    2006-08-01

    Soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3 edges of Co-doped rutile TiO2 at room temperature revealed clear multiplet features characteristic of ferromagnetic Co2+ ions coordinated by O2- ions, being in sharp contrast to the featureless XMCD spectrum of Co metal or metallic clusters. The absorption and XMCD spectra agree well with a full atomic-multiplet calculation for the Co2+ high-spin state in the D2h-symmetry crystal field at the Ti site in rutile TiO2. The results indicate that the ferromagnetism arises from the Co2+ ions substituting the Ti4+ ions.

  5. Acceleration of electrons by a circularly polarized laser pulse in the presence of an intense axial magnetic field in vacuum

    SciTech Connect

    Singh, K. P.

    2006-08-15

    Acceleration of electrons by a circularly polarized laser pulse in the presence of a short duration intense axial magnetic field has been studied. Resonance occurs between the electrons and the laser field for an optimum magnetic field leading to effective energy transfer from laser to electrons. The value of optimum magnetic field is independent of the laser intensity and decreases with initial electron energy. The electrons rotate around the axis of the laser pulse with small angle of emittance and small energy spread. Acceleration gradient increases with laser intensity and decreases with initial electron energy.

  6. Magnetic Nanoparticles with High Specific Absorption Rate at Low Alternating Magnetic Field

    PubMed Central

    Kekalo, K.; Baker, I.; Meyers, R.; Shyong, J.

    2015-01-01

    This paper describes the synthesis and properties of a new type of magnetic nanoparticle (MNP) for use in the hyperthermia treatment of tumors. These particles consist of 2–4 nm crystals of gamma-Fe2O3 gathered in 20–40 nm aggregates with a coating of carboxymethyl-dextran, producing a zetasize of 110–120 nm. Despite their very low saturation magnetization (1.5–6.5 emu/g), the specific absorption rate (SAR) of the nanoparticles is 22–200 W/g at applied alternating magnetic field (AMF) with strengths of 100–500 Oe at a frequency of 160 kHz. PMID:26884816

  7. On a theory of an FEL amplifier with circular waveguide and guiding magnetic field

    SciTech Connect

    Saldin, E.L.; Schneidmiller, E.A.; Yurkov, M.V.

    1995-12-31

    We consider an FEL amplifier with an axisymmetric electron beam, circular waveguide, helical undulator and guiding magnetic field. The presented nonlinear theory of the FEL amplifier is based on Hamiltonian description of particle motion and radiation field representation with Green function method. The space charge fields, energy spread and diffraction effects are taken into consideration. Such an FEL amplifier configuration possesses some peculiarities when it operates in a regime with the negative longitudinal mass (i.e. when{mu}{sup -1}{proportional_to}dv{sub z}/dE < 0). It is shown that in the presence of strong space charge fields, the so-called {open_quotes}negative mass{close_quotes} instability may influence significantly on the FEL amplifier operation resulting in a significant increase in the FEL amplifier efficiency. It is proposed in the presented paper to use the effect of the {open_quotes}negative mass instability{close_quotes} to achieve an effective bunching of the CERN Linear Collider (LIC) driving beam.

  8. Electrochemical titrations and reaction time courses monitored in situ by magnetic circular dichroism spectroscopy.

    PubMed

    Bradley, Justin M; Butt, Julea N; Cheesman, Myles R

    2011-12-15

    Magnetic circular dichroism (MCD) spectra, at ultraviolet-visible or near-infrared wavelengths (185-2000 nm), contain the same transitions observed in conventional absorbance spectroscopy, but their bisignate nature and more stringent selection rules provide greatly enhanced resolution. Thus, they have proved to be invaluable in the study of many transition metal-containing proteins. For mainly technical reasons, MCD has been limited almost exclusively to the measurement of static samples. But the ability to employ the resolving power of MCD to follow changes at transition metal sites would be a potentially significant advance. We describe here the development of a cuvette holder that allows reagent injection and sample mixing within the 50-mm-diameter ambient temperature bore of an energized superconducting solenoid. This has allowed us, for the first time, to monitor time-resolved MCD resulting from in situ chemical manipulation of a metalloprotein sample. Furthermore, we report the parallel development of an electrochemical cell using a three-electrode configuration with physically separated working and counter electrodes, allowing true potentiometric titration to be performed within the bore of the MCD solenoid.

  9. Insoluble protein characterization by circular dichroism (CD) spectroscopy and nuclear magnetic resonance (NMR).

    PubMed

    Goyal, Shaveta; Qin, Haina; Lim, Liangzhong; Song, Jianxing

    2015-01-01

    Besides misfolded proteins, which still retain the capacity to fold into uniquely defined structures but are misled to "off-pathway" aggregation, there exists a group of proteins which are unrefoldable and insoluble in buffers. Previously no general method was available to solubilize them and consequently their solution conformations could not be characterized. Recently, we discovered that these insoluble proteins could in fact be solubilized in pure water. Circular dichroism (CD) spectroscopy and nuclear magnetic resonance (NMR) characterization led to their classification into three groups, all of which lack the tight tertiary packing and consequently anticipated to unavoidably aggregate in vivo with ~150 mM ions, thus designated as "intrinsically insoluble proteins (IIPs)." It appears that eukaryotic genomes contain many "IIP," which also have a potential to interact with membranes to trigger neurodegenerative diseases. In this chapter, we provide a detailed procedure to express and purify these proteins, followed by CD and NMR spectroscopy characterization of their conformation and interaction with dodecylphosphocholine (DPC).

  10. Azimuthally asymmetric eigenmodes of a magnetized plasma cylinder around a dielectric rod in a circular waveguide

    SciTech Connect

    Shlapakovski, A. S.; Krasnitskiy, M. Yu.

    2008-01-15

    The electrodynamics of a circular waveguide with a dielectric rod surrounded by a magnetized plasma layer is considered. A general dispersion relation for azimuthally asymmetric perturbations is derived, and its solutions describing slow waves-specifically, electromagnetic and plasma modes, as well as (and primarily) hybrid waves that combine the properties of both mode types-are investigated numerically. For the fundamental waveguide mode of the system-the HE{sub 11} mode-the parameters of the plasma layer are determined at which the mode cannot be subject to Cherenkov interaction with a relativistic electron beam at a given frequency. For both waveguide and plasma modes, the radial profiles of the longitudinal components of the electric field and Poynting vector, the fractions of RF power carried within the dielectric and plasma regions and vacuum gap, and the coupling impedance are calculated as functions of the parameters of the plasma layer. The evolution of the field structure during the formation of asymmetric hybrid waves is traced. The results of calculating the dispersion and coupling impedance are analyzed as applied to an antenna-amplifier-a relativistic traveling-wave tube operating on the HE{sub 11} mode of the dielectric rod: specifically, the implementability of the concept in the presence of a plasma at the rod surface is estimated, and the possible role of azimuthally asymmetric and symmetric plasma modes is examined.

  11. Magnetic Circular Dichroism Spectroscopy of meso-Tetraphenylporphyrin-Derived Hydroporphyrins and Pyrrole-Modified Porphyrins.

    PubMed

    Rhoda, Hannah M; Akhigbe, Joshua; Ogikubo, Junichi; Sabin, Jared R; Ziegler, Christopher J; Brückner, Christian; Nemykin, Victor N

    2016-07-28

    A large set of free-base and transition-metal 5,10,15,20-tetraphenyl-substituted chlorins, bacteriochlorins, and isobacteriochlorins and their pyrrole-modified analogues were investigated by combined UV-visible spectroscopy, magnetic circular dichroism (MCD), density functional theory (DFT), and time-dependent DFT (TDDFT) approaches and their spectral characteristics were compared to those of the parent compounds, free-base tetraphenylporphyrin 1H2 and chlorin 2H2. It was shown that the nature of the pyrroline substituents in the chlorin derivatives dictates their specific UV-vis and MCD spectroscopic signatures. In all hydroporphyrin-like cases, MCD spectroscopy suggests that the ΔHOMO is smaller than the ΔLUMO for the macrocycle-centered frontier molecular orbitals. DFT and TDDFT calculations were able to explain the large broadening of the UV-vis and MCD spectra of the chlorin diones and their derivatives compared to the other hydroporphyrins and hydroporphyrin analogues. This study contributes to the further understanding of the electronic effects of replacing a pyrrole in porphyrins by pyrrolines or other five-membered heterocycles (oxazoles and imidazoles). PMID:27400337

  12. Novel technique for injecting and extracting beams in a circular hadron accelerator without using septum magnets

    NASA Astrophysics Data System (ADS)

    Franchi, Andrea; Giovannozzi, Massimo

    2015-07-01

    With a few exceptions, all on-axis injection and extraction schemes implemented in circular particle accelerators, synchrotrons, and storage rings, make use of magnetic and electrostatic septa with systems of slow-pulsing dipoles acting on tens of thousands of turns and fast-pulsing dipoles on just a few. The dipoles create a closed orbit deformation around the septa, usually referred to as an orbit bump. A new approach is presented which obviates the need for the septum deflectors. Fast-pulsing elements are still required, but their strength can be minimized by choosing appropriate local accelerator optics. This technique should increase the beam clearance and reduce the usually high radiation levels found around the septa and also reduce the machine impedance introduced by the fast-pulsing dipoles. The basis of the technique is the creation of stable islands around stable fixed points in horizontal phase space. The trajectories of these islands may then be adjusted to match the position and angle of the incoming or outgoing beam.

  13. Sting-free measurements on a magnetically supported right circular cylinder aligned with the free stream

    NASA Astrophysics Data System (ADS)

    Higuchi, Hiroshi; Sawada, Hideo; Kato, Hiroyuki

    The flow over cylinders of varying fineness ratio (length to diameter) aligned with the free stream was examined using a magnetic suspension and balance system in order to avoid model support interference. The drag coefficient variation of a right circular cylinder was obtained for a wide range of fineness ratios. Particle image velocimetry (PIV) was used to examine the flow field, particularly the behaviour of the leading-edge separation shear layer and its effect on the wake. Reynolds numbers based on the cylinder diameter ranged from 5105, while the major portion of the experiment was conducted at ReD=1.0×105. For moderately large fineness ratio, the shear layer reattaches with subsequent growth of the boundary layer, whereas over shorter cylinders, the shear layer remains detached. Differences in the wake recirculation region and the immediate wake patterns are clarified in terms of both the mean velocity and turbulent flow fields, including longitudinal vortical structures in the cross-flow plane of the wake. The minimum drag corresponded to the fineness ratio for which the separated shear layer reattached at the trailing edge of the cylinder. The base pressure was obtained with a telemetry technique. Pressure fields and aerodynamic force fluctuations are also discussed.

  14. Magnetic circular dichroism in the ion yield of polarized chromium atoms at the 2p edge

    SciTech Connect

    Pruemper, G.; Viefhaus, J.; Becker, U.; Kroeger, S.; Mueller, R.; Zimmermann, P.; Martins, M.

    2003-09-01

    The effect of magnetic dichroism in the partial and total ion yield of chromium, i.e., the absorption of polarized chromium vapor was observed in the gas phase. The measurements were performed at the 2p edge and at photon energies above the 2p edge. The structure of the dichroism at the 2p edge can be understood by including the coupling of the 2p hole with the 3d and 4s shells. Our experimental results for the dichroism at the 2p edge are similar to results of solid-state experiments. Implications for the sum rules used as a standard tool to calculate the spin and orbital momentum are discussed.

  15. Circularly polarized microwaves for magnetic resonance study in the GHz range: Application to nitrogen-vacancy in diamonds

    SciTech Connect

    Mrózek, M. Rudnicki, D. S.; Gawlik, W.; Mlynarczyk, J.

    2015-07-06

    The ability to create time-dependent magnetic fields of controlled polarization is essential for many experiments with magnetic resonance. We describe a microstrip circuit that allows us to generate strong magnetic field at microwave frequencies with arbitrary adjusted polarization. The circuit performance is demonstrated by applying it to an optically detected magnetic resonance and Rabi nutation experiments in nitrogen-vacancy color centers in diamond. Thanks to high efficiency of the proposed microstrip circuit and degree of circular polarization of 85%; it is possible to address the specific spin states of a diamond sample using a low power microwave generator. The circuit may be applied to a wide range of magnetic resonance experiments with a well-controlled polarization of microwaves.

  16. Circular dichroism and optical absorption spectra of mononuclear and trinuclear chiral Cu(II) amino-alcohol coordinated compounds: A combined theoretical and experimental study

    NASA Astrophysics Data System (ADS)

    Valencia, Israel; Ávila-Torres, Yenny; Barba-Behrens, Norah; Garzón, Ignacio L.

    2015-04-01

    Studies on the physicochemical properties of biomimetic compounds of multicopper oxidases are fundamental to understand their reaction mechanisms and catalytic behavior. In this work, electronic, optical, and chiroptical properties of copper(II) complexes with amino-alcohol chiral ligands are theoretically studied by means of time-dependent density functional theory. The calculated absorption and circular dichroism spectra are compared with experimental measurements of these spectra for an uncoordinated pseudoephedrine derivative, as well as for the corresponding mononuclear and trinuclear copper(II)-coordinated complexes. This comparison is useful to gain insights into their electronic structure, optical absorption and optical activity. The optical absorption and circular dichroism bands of the pseudoephedrine derivative are located in the UV-region. They are mainly due to transitions originated from n to π anti-bonding orbitals of the alcohol and amino groups, as well as from π bonding to π anti-bonding orbitals of carboxyl and phenyl groups. In the case of the mononuclear and trinuclear compounds, additional signals in the visible spectral region are present. In both systems, the origin of these bands is due to charge transfer from ligand to metal and d-d transitions.

  17. Intensity-dependent circular polarization and circumstellar magnetic fields from the observation of SiO masers

    NASA Technical Reports Server (NTRS)

    Nedoluha, Gerald E.; Watson, William D.

    1994-01-01

    A new aspect of the propagation of astrophysical maser radiation in the presence of a magnetic field is described in which circular polarization is created. The resulting antisymmetric spectral line profile for this circular polarization resembles that produced by the ordinary Zeeman effect when the Zeeman splittings are much less than the spectral line breadth. It is caused by the change, with increasing maser intensity, in the axis of symmetry for the molecular quantum states from a direction that is parallel to the magnetic field to a direction that is parallel to the direction of propagation. When the maser is radiatively saturated, and the rate for stimulated emission is within an order of magnitude of the Zeeman splitting in frequency units, this 'intensity-dependent circular polarization' is greater than that due to the ordinary Zeeman effect by factors as large as 1000. The circular polarization that is observed in the spectra of circumstellar SiO (J = 1-0) masers associated with late-type giants and supergiants may then be caused by magnetic fields as weak as about 10 mG. With the standard Zeeman interpretation of the observations, magnetic fields of 10-100 G are indicated. The lower fields are similar to the limits obtained from the observation of the 22 GHz water masers which are typically somewhat further from the central star. The observed tendency for the fractional linear polarization of SiO masers to increase with increasing angular momentum of the molecular state is shown to be a likely result of anisotropic pumping. Errors are identified that invalidate a recent conflicting claim in the literature about the basic theory of maser polarization in the regime that is relevant here.

  18. SPATIAL DISTRIBUTIONS OF ABSORPTION, LOCAL SUPPRESSION, AND EMISSIVITY REDUCTION OF SOLAR ACOUSTIC WAVES IN MAGNETIC REGIONS

    SciTech Connect

    Chou, D.-Y.; Yang, M.-H.; Zhao Hui; Liang Zhichao; Sun, M.-T.

    2009-11-20

    Observed acoustic power in magnetic regions is lower than the quiet Sun because of absorption, emissivity reduction, and local suppression of solar acoustic waves in magnetic regions. In the previous studies, we have developed a method to measure the coefficients of absorption, emissivity reduction, and local suppression of sunspots. In this study, we go one step further to measure the spatial distributions of three coefficients in two active regions, NOAA 9055 and 9057. The maps of absorption, emissivity reduction, and local suppression coefficients correlate with the magnetic map, including plage regions, except the emissivity reduction coefficient of NOAA 9055 where the emissivity reduction coefficient is too weak and lost among the noise.

  19. Analysis of the near-ultraviolet absorption and circular dichroic spectra of parsley plastocyanin for the effects of pH and copper center conformation changes.

    PubMed

    Durell, S R; Gross, E L; Draheim, J E

    1988-11-15

    The absorption and circular dichroic (CD) spectra of parsley plastocyanin (PC) were measured in order to determine the effects of changes in primary amino acid sequence on both the copper center and protein components of the PC molecule. The near-ultraviolet (uv) absorption and CD spectra of parsley PC were found to be qualitatively similar to those of spinach, poplar, and lettuce PC, except for the near-uv CD spectrum of the reduced form at low pH (ca. pH 5.0). The CD spectrum of reduced parsley PC in the 250-265 nm wavelength region changes from positive to negative ellipticity upon reduction of pH, and is characterized by a pKa value of 5.7. This pKa value is the same as that for the protonation of the histidine 87 copper ligand, observed by NMR, and the change in conformation of the copper center. Similar processes are believed to occur in the other PC species at lower pH values. Thus, the pH-dependent perturbations of the near-uv CD spectra of reduced PC are interpreted as due to transitions in the reduced copper center. The increase in the near-uv absorption spectrum of reduced PC can be divided into pH-independent and pH-dependent portions. The pH-independent portion resembles the absorption spectrum of tetrahedral Cu(I) metallothionein, suggesting the presence of Cu(I)-Cys 84 and/or Cu(I)-Met 92 charge transfer transitions in the near-uv absorption spectra of reduced PC. The pH dependence of the absorption spectrum changes and the pH difference absorption spectrum indicate that tyrosine residues may contribute to at least a part of the pH-dependent portion of the absorption increase of reduced PC.

  20. Ab initio ground state and L{sub 2,3} x-ray magnetic circular dichroism of Mn-based Heusler alloys

    SciTech Connect

    Galanakis, I.; Ostanin, S.; Alouani, M.; Dreysse, H.; Wills, J. M.

    2000-02-01

    Relativistic full-potential calculations within the generalized gradient approximation (GGA) for a series of Mn-based Heusler alloys are presented. Calculated equilibrium lattice parameters deviate less than 1.2% from the experimental values. The main features of a half metallic system are present in the density of states for the PtMnSb and NiMnSb. We predict that PdMnSb shows half metallic character under hydrostatic pressure. The substitution of Sb in PtMnSb by Sn or Te destroys the minority spin band gap. Spin and orbital magnetic moments for all the systems are in good agreement with previous calculations and experimental data. L{sub 2,3} x-ray absorption and x-ray magnetic circular dichroism (XMCD) spectra are calculated for all the five compounds. Pt spectra present big deviations from system to system in the PtMnY (Y=Sn,Sb,Te) compounds while Mn spectra show only small deviations. For all these spectra GGA underestimates the L{sub 3}/L{sub 2} integrated branching ratio and produces a much smaller L{sub 2} peak intensity for the Ni site in NiMnSb. The XMCD sum rules are used to compute the spin and orbital magnetic moments and the results are compared to the direct calculations. (c) 2000 The American Physical Society.

  1. Large anisotropic Fe orbital moments in perpendicularly magnetized Co2FeAl Heusler alloy thin films revealed by angular-dependent x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Okabayashi, Jun; Sukegawa, Hiroaki; Wen, Zhenchao; Inomata, Koichiro; Mitani, Seiji

    2013-09-01

    Perpendicular magnetic anisotropy (PMA) in Heusler alloy Co2FeAl thin films sharing an interface with a MgO layer is investigated by angular-dependent x-ray magnetic circular dichroism. Orbital and spin magnetic moments are deduced separately for Fe and Co 3d electrons. In addition, the PMA energies are estimated using the orbital magnetic moments parallel and perpendicular to the film surfaces. We found that PMA in Co2FeAl is determined mainly by the contribution of Fe atoms with large orbital magnetic moments, which are enhanced at the interface between Co2FeAl and MgO. Furthermore, element specific magnetization curves of Fe and Co are found to be similar, suggesting the existence of ferromagnetic coupling between Fe and Co PMA directions.

  2. Using magnetic circular dichroism for the study of the magnetization and the magnetic moments of atoms in Nd(3)Fe(27.5)Ti(1.5).

    PubMed

    Sarafidis, C; Wilhelm, F; Rogalev, A; Gjoka, M; Kalogirou, O

    2009-06-10

    An element-specific study of the Nd(3)Fe(27.5)Ti(1.5) compound using the hard x-ray magnetic circular dichroism (XMCD) technique is presented. The Nd L(2) and L(3) edge XMCD, as well as the Fe K edge XMCD, were measured in a magnetically oriented sample, parallel and perpendicular to its alignment direction. The XMCD spectra were recorded at three different temperatures, above, below and in between the characteristic peaks that the specific compound presents in AC susceptibility measurements. By probing the Nd L edges and the Fe K edge XMCD, we found that the dipolar R(5d)-Fe(3d) exchange interaction behaves differently with temperature change than the Fe-Fe magnetic interaction. Those differences appear to be in the vicinity of the AC susceptibility characteristic peaks. An XMCD signal was recorded at the Ti K edge, revealing a small orbital polarization due to the hybridization with Fe atomic states. This demonstrates the existence of a small finite magnetic moment in Ti atoms. PMID:21825598

  3. Determination of the Electronic and Magnetic Structures of Sr_2FeMoO6 by Polarized X-ray Absorption

    NASA Astrophysics Data System (ADS)

    Resnick, Damon; Idzerda, Y.; Dvorak, J.; Lussier, A.; Holroyd, J.; Bauer, D.; Ogale, S. B.; Venkatesan, T.

    2002-05-01

    An interest in ferromagnetic oxides has come about through the observation of colossal magnetoresistance (CMR) in perovskite mixed valent manganites. The double perovskite Sr_2FeMoO6 has been established as a new CMR material. Its considerable MR at low fields and room temperature has certain technologically beneficial properties. We have examined the electronic and magnetic structures of Sr_2FeMoO6 with x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). In this study, the valancey of Fe, the magnetism of the Mo sites, temperature effects, and other open issues concerning the basic electronic and magnetic structures are addressed, comparing to recent results [1]. [1] Sugata Ray, Aswani Kumar, D. D. Sarma et al., Phys. Rev. Lett., 87, 097204 (2001)

  4. X-ray magnetic circular dichroism and small angle neutron scattering study of thiol capped gold nanoparticles.

    SciTech Connect

    de la Venta, J.; Bouzas, V.; Pucci, A.; Laguna-Marco, M. A.; Haskel, D.; Pinel, E. F.; te Velthuis, S. G. E.; Hoffmann, A.; Lal, J.; Bleuel, M.; Ruggeri, G.; de Julian, C.; Garcia, M. A.; Univ. Complutense de Madrid; Inst. de Magnetismo Aplicado UCM; Univ. Pisa; Univ. di Padova

    2009-11-01

    X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 {center_dot} 10{sup -4} was found at the Au L{sub 3} edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M{sub s}, of 0.06 emu/g{sub Au}. SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences.

  5. Petal Resonator Surface Coil with a Circular Envelope for High Field Magnetic Resonance Imaging

    NASA Astrophysics Data System (ADS)

    Hidalgo, S. S.; Cuellar, G.; Solis, S. E.; Alejski, A.; Rodríguez, A. O.

    2008-08-01

    A modified version of the petal resonator surface (PERES) coil is proposed in which the petal coils are located inside a circular-shaped coil as opposed to the previous PERES version which did not have a circular envelope. An 8-petal coil was simulated using a finite element method and the quasi-static approach to numerically investigate its electromagnetic characteristics. Numerical simulations showed that the field uniformity is not greatly affected by the use of circular-shaped coil inside in the circular envelope. A coil prototype was developed using the same coil configuration as above and tested on a commercial 3 T imager and a General Electric phantom. Phantom images also demonstrated that the mutual inductance between petals does not alter the coil performance. Standard pulse sequences were used to acquire phantom images with the petal resonator surface coil. It was shown that this prototype resonator coil is fully compatible with clinical high field MR imagers and clinical pulse sequences.

  6. Electronic structure and x-ray magnetic circular dichroism in A2FeReO6 (A =Ca ,Sr ,andBa ) oxides

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.; Bekenov, L. V.; Ernst, A.

    2016-07-01

    A systematic electronic structure study of A2FeReO6 (A =Ba ,Sr ,andCa ) has been performed by employing the local-spin-density approximation (LSDA) and LSDA +U methods using the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We investigated the effects of the subtle interplay between spin-orbit coupling, electron correlations, and lattice distortion on the electronic structure of double perovskites. Ca2FeReO6 has a large distortion in the Fe-O-Re bond, and the electronic structure is mainly determined by electron correlations and lattice distortion. In the Ba -Sr -Ca row, the correlation effects at the Fe site are increased. The correlations at the Re site are small in the Ba- and Sr-based compounds but significant in Ca2FeReO6 . Ca2FeReO6 behaves like an insulator only if considered with a relatively large value of Coulomb repulsion Ueff=2.3 eV at the Re site in addition to Ueff=3.1 eV at the Fe site. Ca2FeReO6 possesses a phase transition at 140 K where the metal-insulator transition (MIT) occurs between metallic high-temperature and insulating low-temperature phases. The spin and orbital magnetic moments are linear functions of temperature before and after the MIT but change abruptly at the point of the phase transition. From theoretically calculated magnetocrystalline anisotropy energy (MAE), we found that the easy axis of magnetization for the low-temperature phase is along the b direction, in agreement with experimental data. We found that the major contribution to the MAE is due to the orbital magnetic anisotropy at the Re site. X-ray-absorption spectra and x-ray magnetic circular dichroism at the Re, Fe, and Ba L2 ,3 and Fe, Ca, and O K edges were investigated theoretically in the frame of the LSDA +U method. A qualitative explanation of the x-ray magnetic circular dichroism spectra shape is provided by an analysis of the corresponding selection rules, orbital character, and occupation numbers of individual orbitals

  7. Microwave absorption properties of carbon nanocoils coated with highly controlled magnetic materials by atomic layer deposition.

    PubMed

    Wang, Guizhen; Gao, Zhe; Tang, Shiwei; Chen, Chaoqiu; Duan, Feifei; Zhao, Shichao; Lin, Shiwei; Feng, Yuhong; Zhou, Lei; Qin, Yong

    2012-12-21

    In this work, atomic layer deposition is applied to coat carbon nanocoils with magnetic Fe(3)O(4) or Ni. The coatings have a uniform and highly controlled thickness. The coated nanocoils with coaxial multilayer nanostructures exhibit remarkably improved microwave absorption properties compared to the pristine carbon nanocoils. The enhanced absorption ability arises from the efficient complementarity between complex permittivity and permeability, chiral morphology, and multilayer structure of the products. This method can be extended to exploit other composite materials benefiting from its convenient control of the impedance matching and combination of dielectric-magnetic multiple loss mechanisms for microwave absorption applications.

  8. Spin-lattice coupling across the singular magnetostructural transition in P r0.5S r0.5Co O3 by x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Padilla-Pantoja, J.; Herrero-Martín, J.; Pellegrin, E.; Gargiani, P.; Valvidares, S. M.; Barla, A.; García-Muñoz, J. L.

    2015-12-01

    We have performed temperature-dependent x-ray magnetic circular dichroism on ferromagnetic P r0.5S r0.5Co O3 at the Co L2 ,3 edges to analyze the correlation of the spin and orbital angular components of the magnetization with the singular magnetostructural anomalies at ˜120 K. We found a sizable orbital angular momentum in Co atoms that follows a temperature dependence very similar to that of the spin momentum. Their sum agrees with the bulk magnetization. Taken together with recent x-ray absorption spectra showing the absence of changes in the electronic filling of Co 3 d states across the magnetostructural transition, our results demonstrate the relevance of the spin-orbit coupling for the stabilization of two distinct ferromagnetic phases in this metallic perovskite. The Co spin-state model is discussed on the basis of charge-transfer multiplet calculations of the dichroic spectral shape.

  9. Magnetic field control of the intraband optical absorption in two-dimensional quantum rings

    NASA Astrophysics Data System (ADS)

    Olendski, O.; Barakat, T.

    2014-02-01

    Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening.

  10. Magnetic field control of the optical absorption in two-dimensional semiconductor rings

    NASA Astrophysics Data System (ADS)

    Olendski, Oleg; Barakat, Thabit

    2014-03-01

    Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers m as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results which allow clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency, is calculated as a function of the magnetic field and levels' broadening. Authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group no RGP-VPP-217.

  11. Magnetic field control of the intraband optical absorption in two-dimensional quantum rings

    SciTech Connect

    Olendski, O.; Barakat, T.

    2014-02-28

    Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening.

  12. Theoretical study of magnetic properties and x-ray magnetic circular dichroism of the ordered Fe{sub 0.5}Pd{sub 0.5} alloy

    SciTech Connect

    Galanakis, I.; Ostanin, S.; Alouani, M.; Dreysse, H.; Wills, J. M.

    2000-01-01

    A detailed theoretical study of magnetic and structural properties of Fe{sub 0.5}Pd{sub 0.5} ordered face-centered tetragonal (fct) alloy, using both the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), is presented. The total energy surface as a function of the lattice parameters a and c shows a long valley where stable structures may exist. Our calculation using the GGA predicts a magnetic phase transition from perpendicular to parallel magnetization as a function of the lattice parameter, whereas LSDA favors always the [001] magnetization axis for all values of the lattice parameters. The spin and orbital magnetic moments and x-ray magnetic circular dichroism spectra are calculated for the easy [001] and the hard [100] magnetization axis and for three sets of experimental lattice parameters, and are compared to the available experimental results on these films. A supercell calculation for a 4 monolayer Fe{sub 0.5}Pd{sub 0.5} thin film produced similar results. While the spin magnetic moments are in fair agreement with experiment, the orbital magnetic moments are considerably underestimated. To improve the agreement with experiment we included an atomic orbital polarization term; however, the computed orbital moments scarcely changed. (c) 2000 The American Physical Society.

  13. Experimental evidence of the B2 and B3 dependent circular birefringence of chiral molecules in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Surma, M.

    The rotation of the plane of polarization of light passing through chiral media in the Faraday geometry of a magnetic field B and light propagation vector k have been measured in high magnetic fields of induction up to 30 T and a laser beam wavelength = 488 nm. The optically active enantiomers of neat alpha-methylbenzylamine and solutions in water of tartaric, malic and lactic acids, leucine and threonine exhibit dependence of the induced rotation of the light polarization plane on B 2 and B 3. The effect is reported of the magnetic field B 2 induced circular birefringence of laevorotatory and dextrorotatory enantiomers. Also differences are found in the effective rotation of the plane of polarization in the parallel (alpha ) and antiparallel (alpha ) configurations of B and k acting on a chiral medium. The first quantitative determination is made of the nonlinear ( B 3) Faraday effect in chiral media. The linear in B circular birefringence makes the largest contribution to the B 2 and B 3 dependent rotation.

  14. Co K-edge magnetic circular dichroism across the spin state transition in LaCoO3 single crystal

    NASA Astrophysics Data System (ADS)

    Efimov, V.; Ignatov, A.; Troyanchuk, I. O.; Sikolenko, V. V.; Rogalev, A.; Wilhelm, F.; Efimova, E.; Tiutiunnikov, S. I.; Karpinsky, D.; Kriventsov, V.; Yakimchuk, E.; Molodtsov, S.; Sainctavit, P.; Prabhakaran, D.

    2016-05-01

    We report on Co K-edge x-ray magnetic circular dichroism (XMCD) measurements of LaCoO3 single crystal in temperature range from 5 to 300 K and external magnetic field of 17 T. The response consists of pre-edge (at 7712 eV) and bi-polar peak (up at 7727, down at 7731 eV) with amplitudes, respectively, less than 10-3 and 10-2 of the Co K-edge jump. Using the sum rule the orbital magnetic moment of 4p Co is evaluated. Its temperature dependence reaches a maximum of (2.7 ± 0.9) x10-3 μB at 120 K, following the trend for the total magnetic moment on the Co obtained from the superconducting quantum interference device measurements. However, on warming from 25 to 120 K, the orbital magnetic moment of the 4p Co doubles while total magnetic moment of Co increases 10 times. First principle calculations are in order to relate the Co K-edge XMCD results to the orbital and spin moment of 3d Co.

  15. Magnetic nanoparticles for power absorption: Optimizing size, shape and magnetic properties

    SciTech Connect

    Gonzalez-Fernandez, M.A.; Torres, T.E.; Andres-Verges, M.; Costo, R.; Presa, P. de la; Serna, C.J.; Morales, M.P.; Marquina, C.; Ibarra, M.R.; Goya, G.F.

    2009-10-15

    We present a study on the magnetic properties of naked and silica-coated Fe{sub 3}O{sub 4} nanoparticles with sizes between 5 and 110 nm. Their efficiency as heating agents was assessed through specific power absorption (SPA) measurements as a function of particle size and shape. The results show a strong dependence of the SPA with the particle size, with a maximum around 30 nm, as expected for a Neel relaxation mechanism in single-domain particles. The SiO{sub 2} shell thickness was found to play an important role in the SPA mechanism by hindering the heat outflow, thus decreasing the heating efficiency. It is concluded that a compromise between good heating efficiency and surface functionality for biomedical purposes can be attained by making the SiO{sub 2} functional coating as thin as possible. - Graphical Abstract: The magnetic properties of Fe{sub 3}O{sub 4} nanoparticles from 5 to 110 nm are presented, and their efficiency as heating agents discussed as a function of particle size, shape and surface functionalization.

  16. Retinoic acid binding properties of the lipocalin member beta-lactoglobulin studied by circular dichroism, electronic absorption spectroscopy and molecular modeling methods.

    PubMed

    Zsila, Ferenc; Bikádi, Zsolt; Simonyi, Miklós

    2002-12-01

    Interaction between the Vitamin A derivative all-trans retinoic acid and the lipocalin member bovine beta-lactoglobulin (BLG) was studied by circular dichroism (CD) and electronic absorption spectroscopy at different pH values. In neutral and alkaline solutions achiral retinoic acid forms a non-covalent complex with the protein as indicated by the appearance of a negative Cotton effect around 347 nm associated to the narrowed and red shifted pi-pi(*) absorption band of the ligand. The induced optical activity is attributed to the helical distortion of the conjugated chain caused by the chiral protein binding environment. As the disappearing CD activity showed in the course of CD-pH titration experiment, retinoic acid molecules dissociate from BLG upon acidification but this release is completely reversible as proved by the reconstitution of the CD and absorption spectra after setting the pH back to neutral. This unique behavior of the complex is explained by the conformational change of BLG (Tanford transition) which involves a movement of the EF loop at the entrance of the central cavity from open to closed conformation in the course of pH lowering. From these results it was inferred that retinoic acid binds within the hydrophobic calyx of the beta-barrel. PMID:12429354

  17. Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism

    SciTech Connect

    Thersleff, Thomas; Rusz, Jan; Rubino, Stefano; Hjörvarsson, Björgvin; Ito, Yasuo; J. Zaluzec, Nestor; Leifer, Klaus

    2015-08-17

    Understanding the ramifications of reduced crystalline symmetry on magnetic behavior is a critical step in improving our understanding of nanoscale and interfacial magnetism. However, investigations of such effects are often controversial largely due to the challenges inherent in directly correlating nanoscale stoichiometry and structure to magnetic behavior. Here, we describe how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic Circular Dichroism (EMCD) signals as a function of scattering angle to locally probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0) surface. Experiments and simulations both reveal a strong dependence of the magnetic orbital to spin ratio on its scattering vector in reciprocal space. We exploit this variation to extract the magnetic properties of the oxide cladding layer, showing that it locally may exhibit an enhanced orbital to spin moment ratio. This finding is supported here by both spatially and angularly resolved EMCD measurements, opening up the way for compelling investigations into how magnetic properties are affected by nanoscale features.

  18. Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism

    PubMed Central

    Thersleff, Thomas; Rusz, Jan; Rubino, Stefano; Hjörvarsson, Björgvin; Ito, Yasuo; J. Zaluzec, Nestor; Leifer, Klaus

    2015-01-01

    Understanding the ramifications of reduced crystalline symmetry on magnetic behavior is a critical step in improving our understanding of nanoscale and interfacial magnetism. However, investigations of such effects are often controversial largely due to the challenges inherent in directly correlating nanoscale stoichiometry and structure to magnetic behavior. Here, we describe how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic Circular Dichroism (EMCD) signals as a function of scattering angle to locally probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0) surface. Experiments and simulations both reveal a strong dependence of the magnetic orbital to spin ratio on its scattering vector in reciprocal space. We exploit this variation to extract the magnetic properties of the oxide cladding layer, showing that it locally may exhibit an enhanced orbital to spin moment ratio. This finding is supported here by both spatially and angularly resolved EMCD measurements, opening up the way for compelling investigations into how magnetic properties are affected by nanoscale features. PMID:26278134

  19. Magnetic fluorescent lamp having reduced ultraviolet self-absorption

    DOEpatents

    Berman, Samuel M.; Richardson, Robert W.

    1985-01-01

    The radiant emission of a mercury-argon discharge in a fluorescent lamp assembly (10) is enhanced by providing means (30) for establishing a magnetic field with lines of force along the path of electron flow through the bulb (12) of the lamp assembly, to provide Zeeman splitting of the ultraviolet spectral line. Optimum results are obtained when the magnetic field strength causes a Zeeman splitting of approximately 1.7 times the thermal line width.

  20. Investigation of the electronic absorption spectra and the circular dichroism spectra of binuclear tetra-. mu. -mandelato complexes of Mo/sub 2//sup 4 +/

    SciTech Connect

    Golovaneva, I.F.; Akhmedov, E.L.; Kotel'nikova, A.S.

    1987-05-01

    The IR, electronic absorption, and circular dichroism spectra of the binuclear tetra-..mu..-mandelates of molybdenum(II) (Mo/sub 2//D-(-)-OOCCH(OH)C/sub 6/H/sub 5///sub 4/) and (Mo/sub 2//L-(+)-OOCCH(OH)C/sub 6/H/sub 5///sub 4/) have been studied. It has been established that Cotton effects are induced in all the electronic transitions of the symmetric (Mo/sub 2/O/sub 8/)chromophore under the influence of the asymmetric atom of the optically active mandelato ligand. The observed electronic transitions have been assigned on the basis of an analysis of the spectroscopic data obtained.

  1. Analysis of the structure of Saturn's magnetic field using charged particle absorption signatures

    SciTech Connect

    Chenette, D.L.; Davis, L. Jr.

    1982-07-01

    A new technique is derived for determining the structure of Saturn's magnetic field. This technique uses the observed positions of charged particle absorption signatures due to the satellites and rings of Saturn to determine the parameters of an axially symmetric, spherical harmonic model of the magnetic field using the method of least squares. Absorption signatures observed along the Pioneer 11, Voyager 1, and Voyager 2 spacecraft trajectories are used to derive values for the orientation of the magnetic symmetry axis relative to Saturn's axis of rotation, the axial displacement of the center of the magnetic dipole from the center of Saturn, and the magnitude of the external field component. Comparing these results with the magnetic field model parameters deduced from analyses of magnetometer data leads us to prefer models that incorporate a northward offset of the dipole center by about 0.05 R/sub s/.

  2. An analysis of the structure of Saturn's magnetic field using charged particle absorption signatures

    SciTech Connect

    Chenette, D.L.; Davis, L. Jr.

    1983-06-01

    A technique is derived for determining the structure of Saturn's magnetic field. This technique uses the observed positions of charged particle absorption signatures due to the satellites and rings of Saturn to determine the parameters of an axially symmetric, spherical harmonic model of the magnetic field using the method of least squares. Absorption signatures observed along the Pioneer 11, Voyager 1, and Voyager 2 spacecraft trajectories are used to derive values for the orientation of the magnetic symmetry axis relative to Saturn's axis of rotation, the axial displacement of the center of the magnetic dipole from the center of Saturn, and the magnitude of the external field component. A comparison of these results with the magnetic field model parameters deduced from analyses of magnetometer data supports models which incorporate a northward offset of the dipole center by about 0.05 R(3).

  3. Interaction between adenovirus DNA-binding protein and single-stranded polynucleotides studied by circular dichroism and ultraviolet absorption.

    PubMed

    van Amerongen, H; van Grondelle, R; van der Vliet, P C

    1987-07-28

    The adenovirus DNA-binding protein (AdDBP) is a multifunctional protein required for viral DNA replication and control of transcription. We have studied the binding of AdDBP to single-stranded M13 DNA and to the homopolynucleotides poly(rA), poly(dA), and poly(dT) by means of circular dichroism (CD) and optical density (OD) measurements. The binding to all these polynucleotides was strong and nearly stoichiometric. Titration experiments showed that the size of the binding site is 9-11 nucleotides long for M13 DNA, poly(dA), and poly(rA). A higher value (15.0 +/- 0.8) was found for poly(dT). Pronounced changes in the circular dichroism and optical density spectra were observed upon binding of AdDBP. In general, both the positive peak around 260-270 nm and the negative peak around 240-250 nm in the CD spectra decreased in intensity, and a shift of the crossover point to longer wavelengths was found. The OD spectra observed upon binding of AdDBP are remarkably similar to those obtained with prokaryotic helix-destabilizing proteins like bacteriophage T4 gene 32 protein and fd gene 5 protein. The data can best be interpreted by assuming that the AdDBP-polynucleotide complex has a regular, rigid, and extended configuration that satifies two criteria: (1) a considerable tilt of the bases in combination with (2) a small rotation per base and/or a shift of the bases closer to the helix axis.

  4. Electronic and spin states of SrRuO3 thin films: An x-ray magnetic circular dichroism study

    NASA Astrophysics Data System (ADS)

    Agrestini, S.; Hu, Z.; Kuo, C.-Y.; Haverkort, M. W.; Ko, K.-T.; Hollmann, N.; Liu, Q.; Pellegrin, E.; Valvidares, M.; Herrero-Martin, J.; Gargiani, P.; Gegenwart, P.; Schneider, M.; Esser, S.; Tanaka, A.; Komarek, A. C.; Tjeng, L. H.

    2015-02-01

    We report a study of the local magnetism in thin films of SrRuO3 grown on (111) and (001) oriented SrTiO3 substrates using x-ray magnetic circular dichroism spectroscopy (XMCD) at the Ru-L2 ,3 edges. The application of the sum rules to the XMCD data gives an almost quenched orbital moment and a spin moment close to the value expected for the low spin state S =1 . Full-multiplet cluster calculations indicate that the low spin state is quite stable and suggest that the occurrence of a transition to the high spin state S =2 in strained thin films of SrRuO3 is unlikely as it would be too expensive in energy.

  5. Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism

    DOE PAGES

    Thersleff, Thomas; Rusz, Jan; Rubino, Stefano; Hjörvarsson, Björgvin; Ito, Yasuo; J. Zaluzec, Nestor; Leifer, Klaus

    2015-08-17

    Understanding the ramifications of reduced crystalline symmetry on magnetic behavior is a critical step in improving our understanding of nanoscale and interfacial magnetism. However, investigations of such effects are often controversial largely due to the challenges inherent in directly correlating nanoscale stoichiometry and structure to magnetic behavior. Here, we describe how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic Circular Dichroism (EMCD) signals as a function of scattering angle to locally probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0) surface. Experiments and simulations both reveal a strong dependence of the magneticmore » orbital to spin ratio on its scattering vector in reciprocal space. We exploit this variation to extract the magnetic properties of the oxide cladding layer, showing that it locally may exhibit an enhanced orbital to spin moment ratio. This finding is supported here by both spatially and angularly resolved EMCD measurements, opening up the way for compelling investigations into how magnetic properties are affected by nanoscale features.« less

  6. Enhancement of specific absorption rate by exchange coupling of the core-shell structure of magnetic nanoparticles for magnetic hyperthermia

    NASA Astrophysics Data System (ADS)

    Phadatare, M. R.; Meshram, J. V.; Gurav, K. V.; Hyeok Kim, Jin; Pawar, S. H.

    2016-03-01

    Conversion of electromagnetic energy into heat by nanoparticles (NPs) has the potential to be a powerful, non-invasive technique for biomedical applications such as magnetic fluid hyperthermia, drug release, disease treatment and remote control of single cell functions, but poor conversion efficiencies have hindered practical applications so far. In this paper, an attempt has been made to increase the efficiency of magnetic thermal induction by NPs. To increase the efficiency of magnetic thermal induction by NPs, one can take advantage of the exchange coupling between a magnetically hard core and magnetically soft shell to tune the magnetic properties of the NP and maximize the specific absorption rate, which is the gauge of conversion efficiency. In order to examine the tunability of magnetocrystalline anisotropy and its magnetic heating power, a representative magnetically hard material (CoFe2O4) has been coupled to a soft material (Ni0.5Zn0.5Fe2O4). The synthesized NPs show specific absorption rates that are of an order of magnitude larger than the conventional one.

  7. Magnetic Absorption of Ultrashort Laser Pulses by Metallic Nano-Particles of Spheroidal Form

    NASA Astrophysics Data System (ADS)

    Grigorchuk, N. I.; Tomchuk, P. M.

    The theory for the energy of magnetic absorption by particles of a nonspherical shape by irradiation of the ultrashort laser pulses of different duration and carrying frequencies is developed. For the particles having the oblate or prolate spheroidal shape there has been found a dependence of this energy on the orientation of the magnetic field upon particle, degree of its deviation from the spherical form, pulse duration, and the magnitude of carrier frequency of the laser ray. An appreciable absorption growth at the length of free electron pass large comparing to the particle size is established. The phenomenological and kinetic approach is compared each with other.

  8. X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100)

    SciTech Connect

    Liu, W. Q.; Xu, Y. B. E-mail: rzhang@nju.edu.cn; Song, M. Y.; Lin, J. G.; Maltby, N. J.; Li, S. P.; Samant, M. G.; Parkin, S. S. P.; Bencok, P.; Steadman, Paul; Dobrynin, Alexey; Zhang, R. E-mail: rzhang@nju.edu.cn

    2015-05-07

    The spin and orbital magnetic moments of the Fe{sub 3}O{sub 4} epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15) μ{sub B}/f.u., which is ∼70% of that for the bulk-like Fe{sub 3}O{sub 4}. A significant unquenched orbital moment up to 0.54 ± 0.05 μ{sub B}/f.u. was observed, which could come from the symmetry breaking at the Fe{sub 3}O{sub 4}/MgO interface. Such sizable orbital moment will add capacities to the Fe{sub 3}O{sub 4}-based spintronics devices in the magnetization reversal by the electric field.

  9. Study of the Effect of the Pulse Width of the Excitation Source on the Two-Photon Absorption and Two-Photon Circular Dichroism Spectra of Biaryl Derivatives.

    PubMed

    Vesga, Yuly; Hernandez, Florencio E

    2016-09-01

    Herein we report on the expanded theoretical calculations and the experimental measurements of the two-photon absorption (TPA) and two-photon circular dichroism (TPCD) spectra of a series of optically active biaryl derivatives (R-BINOL, R-VANOL, and R-VAPOL) using femtosecond pulses. The comparative analysis of the experimental TPCD spectra obtained with our tunable amplified femtosecond system with those previously measured in our group on the same series of compounds in the picosecond regime reveals a decrease in the amplitude of the signal and an improvement in matching with the theory in the former. These results can be explained based on the negligible contribution of excited state absorption (ESA) using femtosecond pulses compared to the picosecond regime. We show how ESA affects both the strength of the signal and the shape of the TPA and TPCD spectra. TPA and TPCD spectra were obtained using the double L-scan technique over a broad spectral range (450-750 nm) using 90 fs pulses at 50 Hz repetition rate produced by an amplified femtosecond system. The theoretical calculations were performed using modern analytical response theory within the time-dependent density functional theory (TD-DFT) approach using CAM-B3LYP and 6-311++G(d,p) basis sets. PMID:27525702

  10. Itinerant ferromagnetism in the As 4p conduction band of Ba0.6K0.4Mn2As2 identified by x-ray magnetic circular dichroism

    DOE PAGES

    Ueland, B. G.; Pandey, Abhishek; Lee, Y.; Sapkota, A.; Choi, Y.; Haskel, D.; Rosenberg, R. A.; Lang, J. C.; Harmon, B. N.; Johnston, D. C.; et al

    2015-05-27

    In this study, x-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba0.6K0.4Mn2As2 show that the ferromagnetism below TC ≈ 100 K arises in the As 4p conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below TC, however, a clear XMCD signal is found at the As K edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic c axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that themore » previously reported itinerant ferromagnetism is associated with the As 4p conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.« less

  11. Numerical analysis of inductive detection of magnetic vortex motion excited with circularly polarized field

    NASA Astrophysics Data System (ADS)

    Ya, Xiaorui; Tanaka, Terumitsu; Matsuyama, Kimihide

    2016-07-01

    In the present study, the rotation and switching of a vortex core in submicron-size square dots were numerically analyzed by micromagnetic simulation. This study clarified that the eigenfrequency of the vortex core is strongly dependent on the magnetostatic energy and that rapid switching can be realized by circularly polarized fields with practical amplitudes at the corresponding eigenfrequency. The inductive detection of vortex core rotation, which can distinguish vortex core polarity, was successfully demonstrated and the structural design of the detector was optimized.

  12. Radiation Pressure-Driven Magnetic Disk Winds in Broad Absorption Line Quasi-Stellar Objects

    NASA Technical Reports Server (NTRS)

    DeKool, Martin; Begelman, Mitchell C.

    1995-01-01

    We explore a model in which QSO broad absorption lines (BALS) are formed in a radiation pressure-driven wind emerging from a magnetized accretion disk. The magnetic field threading the disk material is dragged by the flow and is compressed by the radiation pressure until it is dynamically important and strong enough to contribute to the confinement of the BAL clouds. We construct a simple self-similar model for such radiatively driven magnetized disk winds, in order to explore their properties. It is found that solutions exist for which the entire magnetized flow is confined to a thin wedge over the surface of the disk. For reasonable values of the mass-loss rate, a typical magnetic field strength such that the magnetic pressure is comparable to the inferred gas pressure in BAL clouds, and a moderate amount of internal soft X-ray absorption, we find that the opening angle of the flow is approximately 0.1 rad, in good agreement with the observed covering factor of the broad absorption line region.

  13. H I Absorption from the Epoch of Reionization and Primordial Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Vasiliev, Evgenii O.; Sethi, Shiv K.

    2014-05-01

    We study the impact of primordial magnetic fields on the H I absorption from the epoch of reionization. The presence of these fields results in two distinct effects: (1) the heating of the halos from the decay of the magnetic fields owing to ambipolar diffusion, and (2) an increase in the number of halos owing to additional matter fluctuations induced by magnetic fields. We analyze both of these effects and show that the latter is potentially observable because the number of halos along of line of sight can increase by many orders of magnitude. While this effect is not strongly dependent on the magnetic field strength in the range 0.3-0.6 nG, it is extremely sensitive to the magnetic field power spectral index for the near scale-free models. Therefore, the detection of such absorption features could be a sensitive probe of the primordial magnetic field and its power spectrum. We discuss the detectability of these features with the ongoing and future radio interferometers. In particular, we show that LOFAR might be able to detect these absorption features at z ~= 10 in less than 10 hr of integration if the flux of the background source is 400 mJy.

  14. Circular free-electron laser

    DOEpatents

    Brau, Charles A.; Kurnit, Norman A.; Cooper, Richard K.

    1984-01-01

    A high efficiency, free electron laser utilizing a circular relativistic electron beam accelerator and a circular whispering mode optical waveguide for guiding optical energy in a circular path in the circular relativistic electron beam accelerator such that the circular relativistic electron beam and the optical energy are spatially contiguous in a resonant condition for free electron laser operation. Both a betatron and synchrotron are disclosed for use in the present invention. A free electron laser wiggler is disposed around the circular relativistic electron beam accelerator for generating a periodic magnetic field to transform energy from the circular relativistic electron beam to optical energy.

  15. Strong nuclear ring currents and magnetic fields in pseudorotating OsH4 molecules induced by circularly polarized laser pulses.

    PubMed

    Barth, Ingo; Bressler, Christian; Koseki, Shiro; Manz, Jörn

    2012-06-01

    We design a circularly polarized laser pulse in the infrared frequency and femtosecond time domains, for excitation of the OsH(4) molecule in its first excited pseudorotational state of the triply-degenerate bend. The OsH(4) molecule need not be pre-oriented. After excitation, the central nucleus Os carries out pseudorotation about the axis parallel to the direction of propagation of the laser pulse. This pseudorotation causes a strong electric ring current with a value I=1.53 e fs(-1). The mean value of the radius of the ring current is very small, R=0.0031 a(0), where a(0) is the Bohr radius. According to the Biot-Savart law (|B(R=0)| ~I/R)), this nuclear ring current induces the strongest magnetic field predicted so far in molecules, with a central peak absolute value |B(R=0)| =623 T. To monitor the effect, we propose an IR-pump-X-ray-probe versus an X-ray-probe-only experiment, at the K- and L-edges of X-ray ionization. The results are based on the general quantum theory of excitations of pseudorotations in tetrahedral molecules AB(4), driven by a circularly polarized laser pulse. PMID:22389250

  16. Electronic states of benzo[a]pyrene. Linear and magnetic circular dichroism, polarized fluorescence, and quantum chemical calculations

    SciTech Connect

    Spanget-Larsen, J.; Waluk, J.; Erikksson, S.

    1992-03-11

    The carcinogen benzo[a]pyrene is investigated by UV and IR linear dichroism (LD) spectroscopy in stretched polyethylene, by UV magnetic circular dichroism (MCD) spectroscopy, and by fluorescence polarization spectroscopy. The combined results lead to detailed experimental characterization of transitions in the near-UV region, with determination of polarization directions for five electronic transitions. The experimental results are compared with theoretical predictions using the PPP, CNDO/S, CNDO-SDCI, and LCOAO quantum chemical models. Excellent agreement with observed values in the low-energy region, including transition transition moment directions and MCD signs, is obtained within the LCOAO model. The theoretical analysis reveals a strong breakdown of the alternant pairing symmetry for benzo[a]pyrene, compared with those observed in the related hydrocarbons benz[a]anthracene and chrysene. 44 refs., 7 figs., 4 tabs.

  17. Change in soft magnetic properties of Fe-based metallic glasses during hydrogen absorption and desorption

    SciTech Connect

    Novak, L.; Lovas, A.; Kiss, L.F.

    2005-08-15

    The stress level can be altered in soft magnetic amorphous alloys by hydrogen absorption. The resulting changes in the soft magnetic parameters are reversible or irreversible, depending on the chemical composition. Some of these effects are demonstrated in Fe-B, Fe-W-B, and Fe-V-B glassy ribbons, in which various magnetic parameters are measured mainly during hydrogen desorption. The rate of hydrogen desorption is also monitored by measuring the pressure change in a hermetically closed bomb. The observed phenomena are interpreted on the basis of induced stresses and chemical interactions between the solute metal and hydrogen.

  18. Resonant absorption of kink magnetohydrodynamic waves by a magnetic twist in coronal loops

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Zanyar; Karami, Kayoomars

    2016-10-01

    There is ample evidence of twisted magnetic structures in the solar corona. This motivates us to consider the magnetic twist as the cause of Alfvén frequency continuum in coronal loops, which can support the resonant absorption as a rapid damping mechanism for the observed coronal kink magnetohydrodynamic (MHD) oscillations. We model a coronal loop with a straight cylindrical magnetic flux tube, which has constant but different densities in the interior and exterior regions. The magnetic field is assumed to be constant and aligned with the cylinder axis everywhere except for a thin layer near the boundary of the flux tube, which has an additional small magnetic field twist. Then, we investigate a number of possible instabilities that may arise in our model. In the thin tube thin boundary approximation, we derive the dispersion relation and solve it analytically to obtain the frequencies and damping rates of the fundamental (l = 1) and first/second overtone (l = 2, 3) kink (m = 1) MHD modes. We conclude that the resonant absorption by the magnetic twist can justify the rapid damping of kink MHD waves observed in coronal loops. Furthermore, the magnetic twist in the inhomogeneous layer can cause deviations from P1/P2 = 2 and P1/P3 = 3, which are comparable with the observations.

  19. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    SciTech Connect

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D. A.; Heiman, D.

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  20. Toroidal circular dichroism

    NASA Astrophysics Data System (ADS)

    Raybould, T. A.; Fedotov, V. A.; Papasimakis, N.; Kuprov, I.; Youngs, I. J.; Chen, W. T.; Tsai, D. P.; Zheludev, N. I.

    2016-07-01

    We demonstrate that the induced toroidal dipole, represented by currents flowing on the surface of a torus, makes a distinct and indispensable contribution to circular dichroism. We show that toroidal circular dichroism supplements the well-known mechanism involving electric dipole and magnetic dipole transitions. We illustrate this with rigorous analysis of the experimentally measured polarization-sensitive transmission spectra of an artificial metamaterial, constructed from elements of toroidal symmetry. We argue that toroidal circular dichroism will be found in large biomolecules with elements of toroidal symmetry and should be taken into account in the interpretation of circular dichroism spectra of organics.

  1. Raman spectroscopic detection of sub-picomolar DNA by coupling silver catalyzed silver deposition with circular strand-replacement polymerization on magnetic nanoparticles.

    PubMed

    Gao, Fenglei; Zhu, Zhu; Lei, Jianping; Ju, Huangxian

    2012-11-01

    A novel strategy of dual signal amplification was developed using circular strand-replacement DNA polymerization with a molecular beacon as a switch and silver enhancement on magnetic nanoparticles for the specific Raman spectroscopic detection of DNA down to the sub-picomolar level.

  2. Direct observation of ferromagnetism in grain boundary phase of Nd-Fe-B sintered magnet using soft x-ray magnetic circular dichroism

    SciTech Connect

    Nakamura, T.; Yasui, A.; Kotani, Y.; Iwai, H.; Akiya, T.; Ohkubo, T.; Hono, K.; Hirosawa, S.; Gohda, Y.

    2014-11-17

    We have investigated the magnetism of the grain boundary (GB) phase in a Nd{sub 14.0}Fe{sub 79.7}Cu{sub 0.1}B{sub 6.2} sintered magnet using soft x-ray magnetic circular dichroism (XMCD) at the Fe L{sub 2,3}-edges. Soft XMCD spectra were measured from the fractured surface that was confirmed to be covered with a thin GB phase by Auger electron spectroscopy. The magnetic moment of Fe in the GB phase was estimated to be m{sub GB}=1.4 μ{sub B} at 30 °C using the sum rule analysis for XMCD spectra, which is 60% of that of Fe in the Nd{sub 2}Fe{sub 14}B compound. The temperature dependence of m{sub GB} evaluated with reference to Fe in the Nd{sub 2}Fe{sub 14}B phase indicated that the Curie temperature of the GB phase is more than 50 °C lower compared to that of Nd{sub 2}Fe{sub 14}B.

  3. Alternating magnetic field energy absorption in the dispersion of iron oxide nanoparticles in a viscous medium

    NASA Astrophysics Data System (ADS)

    Smolkova, Ilona S.; Kazantseva, Natalia E.; Babayan, Vladimir; Smolka, Petr; Parmar, Harshida; Vilcakova, Jarmila; Schneeweiss, Oldrich; Pizurova, Nadezda

    2015-01-01

    Magnetic iron oxide nanoparticles were obtained by a coprecipitation method in a controlled growth process leading to the formation of uniform highly crystalline nanoparticles with average size of 13 nm, which corresponds to the superparamagnetic state. Nanoparticles obtained are a mixture of single-phase nanoparticles of magnetite and maghemite as well as nanoparticles of non-stoichiometric magnetite. The subsequent annealing of nanoparticles at 300 °C in air during 6 h leads to the full transformation to maghemite. It results in reduced value of the saturation magnetization (from 56 emu g-1 to 48 emu g-1) but does not affect the heating ability of nanoparticles. A 2-7 wt% dispersion of as-prepared and annealed nanoparticles in glycerol provides high heating rate in alternating magnetic fields allowed for application in magnetic hyperthermia; however the value of specific loss power does not exceed 30 W g-1. This feature of heat output is explained by the combined effect of magnetic interparticle interactions and the properties of the carrier medium. Nanoparticles coalesce during the synthesis and form aggregates showing ferromagnetic-like behavior with magnetization hysteresis, distinct sextets on Mössbauer spectrum, blocking temperature well about room temperature, which accounts for the higher energy barrier for magnetization reversal. At the same time, low specific heat capacity of glycerol intensifies heat transfer in the magnetic dispersion. However, high viscosity of glycerol limits the specific loss power value, since predominantly the Neel relaxation accounts for the absorption of AC magnetic field energy.

  4. Circularly polarized luminescence by visible-light absorption in a chiral O-BODIPY dye: unprecedented design of CPL organic molecules from achiral chromophores.

    PubMed

    Sánchez-Carnerero, Esther M; Moreno, Florencio; Maroto, Beatriz L; Agarrabeitia, Antonia R; Ortiz, María J; Vo, Bryan G; Muller, Gilles; de la Moya, Santiago

    2014-03-01

    Circularly polarized luminescence (CPL) in simple (small, nonaggregated, nonpolymeric) O-BODIPYs (R)-1 and (S)-1 by irradiation with visible light is first detected as proof of the ability of a new structural design to achieve CPL from inherently achiral monochromophore systems in simple organic molecules. The measured level of CPL (|g(lum)|) in solution falls into the usual range of that obtained from other simple organic molecules (10(-5)-10(-2) range), but the latter having more complex architectures since axially chiral chromophores or multichromophore systems are usually required. The new design is based on chirally perturbing the acting achiral chromophore by orthogonally tethering a single axially chiral 1,1'-binaphtyl moiety to it. The latter does not participate as a chromophore in the light-absorption/emission phenomenon. This simple design opens up new perspectives for the future development of new small-sized CPL organic dyes (e.g., those based on other highly luminescent achiral chromophores and/or chirally perturbing moieties), as well as for the improvement of the CPL properties of the organic molecules spanning their use in photonic applications.

  5. Site-Specific Studies on X-Ray Magnetic Circular Dichroism at Fe K Edge for Transition-Metal Ferrites

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kenji; Saito, Fumikazu; Toyoda, Takeshi; Ohkubo, Koichi; Yamawaki, Koji; Mori, Takeharu; Hirano, Keiichi; Tanaka, Masahiko; Sasaki, Satoshi

    2000-10-01

    Experiments on X-ray magnetic circular dichroism (XMCD) were performed with synchrotron radiation for Zn and Mn-Zn ferrites (normal-spinel structure) and Ni, Co and Cu ferrites and magnetite (inverse-spinel structure). The inverse-spinel ferrites have positive-to-negative dispersion-type XMCD signals in the pre-edge region of the Fe K edge, which originate from Fe3+ ions in the A sites. There are no such signals for normal-spinel ferrites. Two kinds of negative-to-positive dispersion-type XMCD signals were observed in 7.119-7.125 keV and 7.122-7.129 keV regions of the main edge, which are caused by a mixture of Fe3+ and Fe2+ ions of the B sites in magnetite and Fe3+ ions of the B sites in the other inverse-spinel ferrites, respectively. The B-site origin of the XMCD main-edge spectra was also confirmed by observation of X-ray resonant magnetic scattering for the 222 reflection of Ni ferrite.

  6. Circular Coinduction

    NASA Technical Reports Server (NTRS)

    Rosu, Grigore; Goguen, Joseph; Norvig, Peter (Technical Monitor)

    2001-01-01

    Circular coinduction is a technique for behavioral reasoning that extends cobasis coinduction to specifications with circularities. Because behavioral satisfaction is not recursively enumerable, no algorithm can work for every behavioral statement. However. algorithms using circular coinduction can prove every practical behavioral result that we know. This paper proves the correctness of circular coinduction and some consequences.

  7. Acoustic Power Absorption and its Relation to Vector Magnetic Field of a Sunspot

    NASA Astrophysics Data System (ADS)

    Gosain, S.; Mathew, S. K.; Venkatakrishnan, P.

    2011-02-01

    The distribution of acoustic power over sunspots shows an enhanced absorption near the umbra - penumbra boundary. Previous studies revealed that the region of enhanced absorption coincides with the region of strongest transverse potential field. The aim of this paper is to i) utilize the high-resolution vector magnetograms derived using Hinode SOT/SP observations and study the relationship between the vector magnetic field and power absorption and ii) study the variation of power absorption in sunspot penumbrae due to the presence of spine-like radial structures. It is found that i) both potential and observed transverse fields peak at a similar radial distance from the center of the sunspot, and ii) the magnitude of the transverse field, derived from Hinode observations, is much larger than the potential transverse field derived from SOHO/MDI longitudinal-field observations. In the penumbra, the radial structures called spines (intra-spines) have stronger (weaker) field strength and are more vertical (horizontal). The absorption of acoustic power in the spine and intra-spine shows different behavior, with the absorption being larger in the spine as compared to the intra-spine.

  8. Specific absorption rate determination of magnetic nanoparticles through hyperthermia measurements in non-adiabatic conditions

    NASA Astrophysics Data System (ADS)

    Coïsson, M.; Barrera, G.; Celegato, F.; Martino, L.; Vinai, F.; Martino, P.; Ferraro, G.; Tiberto, P.

    2016-10-01

    An experimental setup for magnetic hyperthermia operating in non-adiabatic conditions is described. A thermodynamic model that takes into account the heat exchanged by the sample with the surrounding environment is developed. A suitable calibration procedure is proposed that allows the experimental validation of the model. Specific absorption rate can then be accurately determined just from the measurement of the sample temperature at the equilibrium steady state. The setup and the measurement procedure represent a simplification with respect to other systems requiring calorimeters or crucial corrections for heat flow. Two families of magnetic nanoparticles, one superparamagnetic and one characterised by larger sizes and static hysteresis, have been characterised as a function of field intensity, and specific absorption rate and intrinsic loss power have been obtained.

  9. Control of Meridional Flow in Circular Cylinders by a Travelling Axial Magnetic Field

    NASA Technical Reports Server (NTRS)

    Mazuruk, K.; Ramachandran, N.; Volz, M. P.

    1999-01-01

    Convective flow in a Bridgman or float zone configuration significantly affects the interface shape and segregation phenomena. While the primary causative factor for this flow is buoyancy induced convection in an enclosed Bridgman melt, the presence of a free surface gives rise to surface tension driven flows in the floating zone processing of melts. It is of interest to curtail these flows in order to realize near quiescent growth conditions that have shown to result in crystals with good longitudinal and radial homogeneity and thereby of better overall quality. While buoyancy effects can be reduced by careful processing in a low gravity (space) environment, the reduction of Marangoni flows due to surface tension variations is not that straight forward. Attempts have been made with some limited success with the use of external fields to affect the melt thermo-fluid behavior. The use of a static magnetic field that reduces convective contamination through the effects of a non-intrusively induced, dissipative Lorentz force in an electrically conducting melt is one such approach. Experiments have shown that axial fields of the order of 5 Tesla can significantly eliminate convection and yield close to diffusion limited crystal growth conditions. The generation and use of such high magnetic fields require substantial hardware and incur significant costs for its operation. Lately, the use of rotating magnetic fields has been tested in semiconductor crystal growth. The method is fairly well known and commonly used in metal processing but its adaptation to crystal growth of semiconductors is fairly recent. The elegance of the technique rests in its low power requirement (typically 10-20 milli-Tesla at 50-400 Hz) and its efficacy in curtailing deleterious temperature fluctuations in the melt. A rotating magnetic field imposes a rotational force and thereby induces a circulation within the melt that tends to dominate other sporadic convective effects. Thus a known low level

  10. Magnetic and microwave absorption properties of ZnCo-substituted W-type strontium hexaferrite

    NASA Astrophysics Data System (ADS)

    Farhadizadeh, A. R.; Seyyed Ebrahimi, S. A.; Masoudpanah, S. M.

    2015-05-01

    Single phase ZnCo-substituted W-type strontium hexaferrite (SrZn2-xCoxFe16O27 with x=0-2.0) were prepared by ceramic conventional method. With the Co substitution, the saturation magnetization increases up to a maximum of 72.8 emu/g for SrZnCoFe16O27, and then decreases, while the coercivity decreases from 1000 Oe for x=0 to 430 Oe for x=1 and then increases up to 700 Oe for x=2. The microwave absorption measurements in the microwave frequency range of 8-12 GHz (X-band) exhibited the maximum absorption of -28 dB at 10.3 GHz with an absorption bandwidth of more than 2.1 GHz for x=1.

  11. Magnetic circular dichroism studies of matrix-isolated atoms: Excited state spin-orbit coupling constant reduction of copper in the noble gases

    NASA Astrophysics Data System (ADS)

    Vala, Martin; Zeringue, Kyle; ShakhsEmampour, Jalal; Rivoal, Jean-Claude; Pyzalski, Robert

    1984-03-01

    The absorption and magnetic circular dichroism spectra of the 2P←2S transition of matrix-isolated copper atoms have been measured in krypton and xenon matrices. A dramatic reversal in the MCD C term pattern is observed. From a spectral band moment analysis it is shown that: (1) noncubic lattice cage vibrational motions are more important than cubic ones in contributing to the observed bandwidths and (2) the Cu excited state spin-orbit coupling constant (λ) in krypton is reduced to 57% of its gas phase value, whereas in xenon it is reduced to -14% of its gas phase value. Calculations using the Moran model show that the excited state geometry of the metal/rare gas cage is distorted via the Jahn-Teller effect in opposite ways in krypton and xenon matrices. The negative sign of λ in xenon reveals a reversal in the order of the 2P state spin-orbit multiplets. Neither this reversal nor the reduction of λ in krypton can be accounted for by the Jahn-Teller effect. We attribute the spin-orbit constant reduction to the overlap of the Cu 4p orbital with the np of the rare gas matrix cage atoms. The calculated spin-orbit reduction factors (in Ar, Kr, and Xe) agree well with the experimental ones if a contracted Cu 4p orbital is used. In the same way the ground state g factor shift with matrix atom type, observed by Kasai and McLeod, is semiquantitatively accounted for by calculation of the overlaps between the Cu 4s orbital and the np orbitals of the rare gas cage atoms.

  12. High pressure study of gadolinium (silicon-germanium) giant magnetocaloric materials using x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Tseng, Yuan-Chieh

    The role of Si-doping in enhancing the magnetic ordering temperature (Tc) of Gd5(SixGe1--x )4 giant magnetocaloric compounds was investigated using x-ray magnetic circular dichroism (XMCD) and diamond anvil cell (DAC) techniques. The purpose of the study is to understand the mechanism of doping-induced ferromagnetic order in these compounds that may advance the magnetic refrigeration technology. The results demonstrate that hydrostatic pressure leads to similar effects as Si-doping for x ≥ 0.125 because the P-T phase diagram reproduces the most notable features of the x-T phase diagram, indicating that the magnetic properties of these compounds are volume-driven. The low-x (0 < x ≤ 0.75) region exhibits an inhomogeneous magneto-structural ground state featured by a mixed antiferromagnetic (orthorhombic (II))--ferromagnetic (orthorhombic (I)) phase at low temperature. Pressure was found to remove this magneto-structural inhomogeneity by fully restoring the magnetization that is obtained for x ≥ 0.125. However, unlike the nearly constant dTc/dP obtained for 0.125 ≤ x < 0.5, dTc/dP of the low-x samples is strongly x-dependent. This suggests that the emergence of the ferromagnetic order from within the antiferromagnetic phase of Gd 5Ge4 parent compound cannot be simply described as a volume-effect due to the existence of the magneto-structural inhomogeneity. Finally, the quantitative correspondence between Si-doping and hydrostatic pressure was examined in order to know if the properties of these materials are monotonically volume-dependent. It was found that Si-doping increases Tc much more effectively than pressure, by a factor of ˜ 11 for a given volume reduction. A local lattice contraction was found around Si atoms as a result of the substitution of Ge by the smaller Si atoms resulting in a remarkably high local chemical pressure. This local contraction results in a stronger Si 3p-Gd 5d orbital hybridization benefiting the indirect ferromagnetic exchange

  13. Room-temperature photomagnetism in the spinel ferrite (Mn,Zn,Fe)3O4 as seen via soft x-ray magnetic circular dichroism

    SciTech Connect

    Bettinger, J.S.; Piamonteze, C.; Chopdekar, R.V.; Liberati, M.; Arenholz, E.; Suzuki, Y.

    2009-08-01

    We have used X-ray magnetic circular dichroism (XMCD) in conjunction with multiplet simulations to directly probe the origin of photomagnetism in nanocrystalline (Mn,Zn,Fe){sub 3}O{sub 4}. A photomagnetic effect at room temperature has been observed in these films with HeNe illumination. We have verified an intervalence charge transfer among octahedral Fe cations to account for the increase in magnetization observed at and above room temperature in small magnetic fields. Using XMCD, we demonstrate that the dichroism of Fe in octahedral sites increases by 18% at room temperature while the dichroism of Fe in tetrahedral sites does not change.

  14. Vibrational absorption and vibrational circular dichroism spectra of leucine in water under different pH conditions: Hydrogen-bonding interactions with water

    NASA Astrophysics Data System (ADS)

    Poopari, Mohammad Reza; Zhu, Peiyan; Dezhahang, Zahra; Xu, Yunjie

    2012-11-01

    Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy have been used to study leucine, a flexible branched-chain amino acid, in aqueous solution. The VA spectra in the range of 1800-1250 cm-1 of leucine in D2O under three representative pHs from strongly acidic (pH = 1), near neutral (pH = 6), to strongly basic (pH = 13), have been measured. The related VCD spectrum has been obtained under near neutral condition. Searches have been carried out to identify the most stable conformers of the Zwitterionic, protonated, and deprotonated forms of leucine in water. The geometry optimization, harmonic frequency calculations, and VA and VCD intensities have been computed at the B3LYP/6-311++G(d,p) level with the implicit polarizable continuum solvation model. While the observed VA spectra under three pHs can be well interpreted with the inclusion of the implicit solvation model, both implicit and explicit solvation models have been found to be crucial for the adequate interpretation of the complex VCD features observed. Molecular dynamics simulations and radial distribution functions have been used to aid the modeling of the leucine-(water)N clusters. It has been recognized that the insertion of a water molecule between the COO- and NH3+ functional groups in the explicit solvated clusters is critical to reproduce the VCD signatures observed. Furthermore, the inclusion of the implicit bulk water environment has been found to be essential to lock water molecules, which are directly hydrogen bonded to leucine, into the positions expected in solution. The application of the explicit and implicit solvation models simultaneously allows new insights into the hydrogen bonding network surrounding leucine in aqueous solution and the role of the surrounding bulk water in stabilizing such hydrogen-bonding network.

  15. Broadening the absorption bandwidth of metamaterial absorbers by transverse magnetic harmonics of 210 mode

    PubMed Central

    Long, Chang; Yin, Sheng; Wang, Wei; Li, Wei; Zhu, Jianfei; Guan, Jianguo

    2016-01-01

    By investigating a square-shaped metamaterial structure we discover that wave diffraction at diagonal corners of such a structure excites transverse magnetic harmonics of 210 mode (TM210 harmonics). Multi-layer overlapping and deliberately regulating period length between adjacent unit cells can significantly enhance TM210 harmonics, leading to a strong absorption waveband. On such a basis, a design strategy is proposed to achieve broadband, thin-thickness multi-layered metamaterial absorbers (MMAs). In this strategy big pyramidal arrays placed in the “white blanks” of a chessboard exhibit two isolated absorption bands due to their fundamental and TM210 harmonics, which are further connected by another absorption band from small pyramidal arrays in the “black blanks” of the chessboard. The as-designed MMA at a total thickness (h) of 4.36 mm shows an absorption of above 0.9 in the whole frequency range of 7–18 GHz, which is 38% broader with respect to previous design methods at the same h. This strategy provides an effective route to extend the absorption bandwidth of MMAs without increasing h. PMID:26888365

  16. Broadening the absorption bandwidth of metamaterial absorbers by transverse magnetic harmonics of 210 mode.

    PubMed

    Long, Chang; Yin, Sheng; Wang, Wei; Li, Wei; Zhu, Jianfei; Guan, Jianguo

    2016-01-01

    By investigating a square-shaped metamaterial structure we discover that wave diffraction at diagonal corners of such a structure excites transverse magnetic harmonics of 210 mode (TM210 harmonics). Multi-layer overlapping and deliberately regulating period length between adjacent unit cells can significantly enhance TM210 harmonics, leading to a strong absorption waveband. On such a basis, a design strategy is proposed to achieve broadband, thin-thickness multi-layered metamaterial absorbers (MMAs). In this strategy big pyramidal arrays placed in the "white blanks" of a chessboard exhibit two isolated absorption bands due to their fundamental and TM210 harmonics, which are further connected by another absorption band from small pyramidal arrays in the "black blanks" of the chessboard. The as-designed MMA at a total thickness (h) of 4.36 mm shows an absorption of above 0.9 in the whole frequency range of 7-18 GHz, which is 38% broader with respect to previous design methods at the same h. This strategy provides an effective route to extend the absorption bandwidth of MMAs without increasing h. PMID:26888365

  17. X-ray absorption spectroscopy on magnetic nanoscale systems for modern applications

    NASA Astrophysics Data System (ADS)

    Schmitz-Antoniak, Carolin

    2015-06-01

    X-ray absorption spectroscopy facilitated by state-of-the-art synchrotron radiation technology is presented as a powerful tool to study nanoscale systems, in particular revealing their static element-specific magnetic and electronic properties on a microscopic level. A survey is given on the properties of nanoparticles, nanocomposites and thin films covering a broad range of possible applications. It ranges from the ageing effects of iron oxide nanoparticles in dispersion for biomedical applications to the characterisation on a microscopic level of nanoscale systems for data storage devices. In this respect, new concepts for electrically addressable magnetic data storage devices are highlighted by characterising the coupling in a BaTiO3/CoFe2O4 nanocomposite as prototypical model system. But classical magnetically addressable devices are also discussed on the basis of tailoring the magnetic properties of self-assembled ensembles of FePt nanoparticles for data storage and the high-moment material Fe/Cr/Gd for write heads. For the latter cases, the importance is emphasised of combining experimental approaches in x-ray absorption spectroscopy with density functional theory to gain a more fundamental understanding.

  18. Enhancing ferromagnetic resonance absorption for very thin insulating magnetic films with spin plasmonics

    NASA Astrophysics Data System (ADS)

    Chui, S. T.

    2015-05-01

    We consider enhancing the ferromagnetic resonance (FMR) absorption of very thin insulating magnetic films by placing it on top of a dielectric. We find that the signal is enhanced by at least an order of magnitude due to a new nonreciprocal interface resonance that is a mixture of the magnetic surface plasmon mode and a wave guide mode. This resonance occurs over a wide range of thicknesses of the dielectric that is still much less than the wavelength and is made possible by the negative magnetic susceptibility of the magnetic layer. The line width of absorption is reduced by an order of magnitude less than the Gilbert damping parameter. At some frequency, the group velocity of this resonance is negative. Experimentally, very thin yttrium iron garnet (YIG) films are grown on a Gadolinium Gallium Garnet (GGG) substrate which can be considered the dielectric. Our model applies to experiments performed in the YIG/GGG system. Indeed, our picture resolves the disagreement on the magnitude of the spin diffusion lengths obtained with the FMR and the Brillouin scattering techniques. It also provides for a way to make new adaptive thin film miniaturized photonic nonreciprocal devices with low loss.

  19. Enhancing ferromagnetic resonance absorption for very thin insulating magnetic films with spin plasmonics

    SciTech Connect

    Chui, S. T.

    2015-05-14

    We consider enhancing the ferromagnetic resonance (FMR) absorption of very thin insulating magnetic films by placing it on top of a dielectric. We find that the signal is enhanced by at least an order of magnitude due to a new nonreciprocal interface resonance that is a mixture of the magnetic surface plasmon mode and a wave guide mode. This resonance occurs over a wide range of thicknesses of the dielectric that is still much less than the wavelength and is made possible by the negative magnetic susceptibility of the magnetic layer. The line width of absorption is reduced by an order of magnitude less than the Gilbert damping parameter. At some frequency, the group velocity of this resonance is negative. Experimentally, very thin yttrium iron garnet (YIG) films are grown on a Gadolinium Gallium Garnet (GGG) substrate which can be considered the dielectric. Our model applies to experiments performed in the YIG/GGG system. Indeed, our picture resolves the disagreement on the magnitude of the spin diffusion lengths obtained with the FMR and the Brillouin scattering techniques. It also provides for a way to make new adaptive thin film miniaturized photonic nonreciprocal devices with low loss.

  20. Comparative study of optical absorption and circular dichroism of bacteriochlorophyll oligomers in Triton X-100, the antenna pigment B850, and the primary donor P-860 of photosynthetic bacteria indicates that all are similar dimers of bacteriochlorophyll a

    PubMed Central

    Scherz, A.; Rosenbach-Belkin, V.

    1989-01-01

    Dimers of bacteriochlorophyll a (Bchla) with optical absorption maximum at 853 nm and a nonconservative circular dichroism spectrum are formed in a solution of formamide/water that contains micelles of Triton X-100. The apparent equilibrium constant and the corresponding Gibbs energy change for the Bchl self-organization are 4.9 × 106 M-1 and -9.2 kcal/mol, respectively. The experimental absorption and circular dichroism spectra of the in vitro Bchl dimer (termed Bchl-853) are similar to the spectra of the bacterial light-harvesting complex B850 and the primary electron donor P-860 and probably point to a common structural motif. Indeed, simulation of the dimers' spectra (optical absorption and circular dichroism), achieved by using an extended version of the exciton theory, suggests the same geometry as recently elucidated for P-860 by x-ray diffraction crystallography. The proposed geometry is predicted to have the minimum energy in the gas phase. In conclusion, the spectral properties of the bathochromically shifted forms of Bchla are likely a result of strong dipolar interactions in self-organized structures of Bchls. PMID:16578840

  1. Packing 360∘ domain walls of identical circulation on planar ferromagnetic nanowires with notches using circular magnetic fields

    NASA Astrophysics Data System (ADS)

    Kaya, F. I.; Sarella, A.; Wang, D.; Tuominen, M.; Aidala, K. E.

    2016-05-01

    360∘ domain walls (DWs) have generated substantial interest with the recognition that their minimal stray field creates only short range interactions, leading to a potentially higher packing density for data storage devices compared to 180∘ DWs. The topology of neighboring 360∘ DWs with identical circulation allows a higher packing density than that of 360∘ DWs of opposite circulation. Our simulations demonstrate the process by which we can pack 360∘ DWs of identical circulation on a long wire with 100 nm width (in y) and 4 nm thickness (in z), studying different size and shape notches to pin the DWs. The process to generate these walls follows a series of circular fields with non-uniform magnetic field strength that decreases as 1/r as if created by an infinitely long wire passing current into or out of the page and centered just above the notches. We are able to pin two 360∘ DWs of the same circulation on adjacent 16 nm (x) by 32 nm (y) rectangular notches 100 nm apart and on adjacent triangular notches of the same area that are 100 nm apart. The location and strength required of the series of fields is different for the different notches. Such stable high density packing of 360∘ DWs in simulations is unprecedented and suggests the potential for high density information storage.

  2. TD-DFT investigation of the magnetic circular dichroism spectra of some purine and pyrimidine bases of nucleic acids.

    PubMed

    Fahleson, Tobias; Kauczor, Joanna; Norman, Patrick; Santoro, Fabrizio; Improta, Roberto; Coriani, Sonia

    2015-05-28

    We present a computational study of the magnetic circular dichroism (MCD) spectra in the 200-300 nm wavelength region of purine and its derivative hypoxanthine, as well as of the pyrimidine bases of nucleic acids uracil, thymine, and cytosine, using the B3LYP and CAM-B3LYP functionals. Solvent effects are investigated within the polarizable continuum model and by inclusion of explicit water molecules. In general, the computed spectra are found to be in good agreement with the experimental ones, apart from some overall blue shifts. Both the pseudo-A term shape of the MCD spectra of the purines and the B term shape of the spectra of pyrimidine bases are reproduced. Our calculations also correctly reproduce the reversed phase of the MCD bands in purine compared to that of its derivatives present in nucleic acids. Solvent effects are sizable and system specific, but they do not in general alter the qualitative shape of the spectra. The bands are dominated by the bright π → π* transitions, and our calculations in solution nicely reproduce their energy differences, improving the estimates obtained in the gas phase. Shoulders are predicted for purine and uracil due to n → π* excitations, but they are too weak to be observed in the experiment.

  3. Specific absorption rate calculations of magnetite, using a modified linear response model for applications in magnetic hyperthermia

    SciTech Connect

    Hernández S, A. E-mail: meduardo2001@hotmail.com; Cano, M. E. E-mail: meduardo2001@hotmail.com; Torres-Arenas, J.

    2014-11-07

    Currently the absorption of electromagnetic radiation by magnetic nanoparticles is studied for biomedical applications of cancer thermotherapy. Several experiments are conduced following the framework of the Rosensweig model, in order to estimate their specific absorption rate. Nevertheless, this linear approximation involves strong simplifications which constrain their accuracy and validity range. The main aim of this work is to incorporate the deviation of the sphericity assumption in particles shapes, to improve the determination of their specific absorption rate. The correction to the effective particles volume is computed as a measure of the apparent amount of magnetic material, interacting with the external AC magnetic field. Preliminary results using the physical properties of Fe3O4 nanoparticles, exhibit an important correction in their estimated specific absorption rate, as a function of the apparent mean particles radius. Indeed, we have observed using a small deviation (6% of the apparent radius), up to 40% of the predicted specific absorption rate by the Rosensweig linear approximation.

  4. Results of stretched wire field integral measurements on the mini-undulator magnet -- comparison of results obtained from circular and translational motion of the integrating wire

    SciTech Connect

    Solomon, L.

    1998-05-01

    Measurements of the multipole content of the Mini-Undulator magnet have been made with two different integrating wire techniques. Both measurements used 43 strand Litz wire stretched along the length of the magnet within the magnet gap. In the first technique, the wire motion was purely translational, while in the second technique the wire was moved along a circular path. The induced voltage in the Litz wire was input into a Walker integrator, and the integrator output was analyzed as a function of wire position for determination of the multipole content of the magnetic field. The mini-undulator magnet is a 10 period, 80 mm per period hybrid insertion device. For all the data contained herein the magnet gap was set at 49 mm. In the mini-undulator magnet, the iron poles are 18mm x 32mm x 86 mm, and the Samarium Cobalt permanent magnet blocks are 22mm x 21mm x 110mm. For this magnet, which is a shortened prototype for the NSLS Soft X-Ray Undulator Magnet, the undulator parameter K = 0.934 B (Tesla){lambda}(cm), and B(tesla) = 0.534/sinh({pi}Gap/{lambda}). At a gap of 49 mm, the magnetic field is 1590 Gauss.

  5. Experimental Study on Interlayer Magnetic Coupling in Sputtered Al/Fe/Al/Gd Magnetic Multilayer Films: II. Hysteresis Curves of X-ray Magnetic Circular Dicroism at the Gd-L3 Edge

    NASA Astrophysics Data System (ADS)

    Nobuhiko Sakai,; Ritthikrai Chai-Ngam,; Akihisa Koizumi,; Hisao Kobayashi,

    2010-06-01

    The spacer thickness dependence of the interlayer magnetic coupling (IMC) between Gd and Fe layers separated by Al spacers has been studied. Magnetization measurement and X-ray magnetic circular dicroism (XMCD) spectroscopy at the Gd-L3 edge have been carried out on sputtered Fe (20 Å)/Al (R Å)/Gd (40 Å) multilayer films (MLFs) for R = 0, 5, 10, and 100 and on some reference films. Experimental data at low magnetic fields below 1 kOe are carefully investigated. A simple theoretical model is introduced to evaluate the strength of IMC. The energy of IMC is represented by the term J MFe \\cdot MGd, in which MFe and MGd denote the average overall magnetic moments of Fe and Gd layers, respectively. It is found that J, which is evaluated from the magnetization curves and the Gd-XMCD signals, is 370 × 104 Oe\\cdotcm2/emu for MLF of R = 0, and can be reduced by one order of magnitude when R is changed from 0 to 10. Most of characteristic features of the experimental data are ascribed to the varing magnetization of Gd layers. It is found that 40 Å Gd layers, which are paramagnetic at 5 K when isolated using 100 Å Al spacers, show magnetic hysteresis when sandwiched between Fe layers.

  6. Influence of Magnetic Losses on Microwave Absorption by Carbon-Nanotube Nanocomposites with a Low Concentration of Ferromagnetic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Avramchuk, A. V.; Kasperovich, M. M.; Pevneva, N. A.; Gusinsky, A. V.; Korolik, O. V.; Tivanov, M. S.; Shulitski, B. G.; Labunov, V. A.; Danilyuk, A. L.; Komissarov, I. V.; Prischepa, S. L.

    2016-05-01

    The absorption properties of magnetic nanocomposites based on carbon nanotubes with a low concentration of ferromagnetic nanoparticles have been investigated in the 78-118 GHz frequency range. A correlation was established between the absorption properties of the nanocomposites and the character of the magnetostatic interaction between nanoparticles.

  7. Parametric excitation of coupled fast and slow upper hybrid waves by counter-propagating circularly polarized lasers in a magnetized plasma

    NASA Astrophysics Data System (ADS)

    Verma, Kanika; Baliyan, Sweta; Sajal, Vivek; Kumar, Ravindra; Sharma, Navneet K.

    2016-07-01

    The parametric decay of large amplitude non-resonant beating mode of counter-propagating lasers (having a frequency difference ≥ 2 ω p ) into a pair of upper hybrid waves is studied in magnetized plasma. One of the excited upper hybrid waves (known as fast wave) having phase velocity close to c , can be utilized for electron acceleration. The coupled mode equations of fast and slow upper hybrid waves are modelled by solving equation of motion and continuity equation simultaneously (using the density perturbation technique) to derive the dispersion relation for two plasmon decay process. The growth rate of the present excitation process using right circularly polarized beating lasers is higher as compared with the growth rates of the excitation processes using ordinary and extraordinary beating lasers. However, the growth rate is not significant in the case of left circularly polarized beating lasers. The growth rate ˜ 0.15 ω p s - 1 is achieved for right circularly polarized beating lasers having v 1 , 2 / c = 0.1 for scattering angle θ s ˜ 160 ° and applied magnetic field ˜ 90 T. The growth rate of fast upper hybrid wave was reduced with the applied axial magnetic field in the present case. The present work is not only significant for the electron acceleration by fast upper hybrid wave but also for diagnostic purpose.

  8. Irreversible rapid changes of magnetic field associated with the 2012 October 23 circular near-limb X1.8 Flare

    NASA Astrophysics Data System (ADS)

    Ye, Dan-Dan; Liu, Chang; Wang, Haimin

    2016-06-01

    It has been found that photospheric magnetic fields can change in accordance with restructuring of the three-dimensional magnetic field following solar eruptions. Previous studies mainly use vector magnetic field data taken for events near the disk center. In this paper, we analyze the magnetic field evolution associated with the 2012 October 23 X1.8 flare in NOAA AR 11598 that is close to the solar limb, using both the 45 s cadence line-of-sight and 12 min cadence vector magnetograms from the Helioseismic and Magnetic Imager on board Solar Dynamics Observatory. This flare is classified as a circular-ribbon flare with spine-fan type magnetic topology containing a null point. In the line-of-sight magnetograms, there are two apparent polarity inversion lines (PILs). The PIL closer to the limb is affected more by the projection effect. Between these two PILs there lie positive polarity magnetic fields, which are surrounded by negative polarity fields outside the PILs. We find that after the flare, both the apparent limb-ward and disk-ward negative fluxes decrease, while the positive flux in-between increases. We also find that the horizontal magnetic fields have a significant increase along the disk-ward PIL, but in the surrounding area, they decrease. Synthesizing the observed field changes, we conclude that the magnetic fields collapse toward the surface above the disk-ward PIL as depicted in the coronal implosion scenario, while the peripheral field turns to a more vertical configuration after the flare. We also suggest that this event is an asymmetric circular-ribbon flare: a flux rope is likely present above the disk-ward PIL. Its eruption causes instability of the entire fan-spine structure and the implosion near that PIL.

  9. Nonlinear dynamics of circularly polarized laser pulse propagating in a magnetized plasma with superthermal ions and mixed nonthermal high-energy tail electrons distributions

    NASA Astrophysics Data System (ADS)

    Etemadpour, R.; Sepehri Javan, N.; Dorranian, D.

    2016-05-01

    The nonlinear dynamics of a circularly polarized laser pulse propagating in the magnetized plasmas whose constituents are superthermal ions and mixed nonthermal high-energy tail electrons is studied theoretically. A nonlinear equation which describes the dynamics of the slowly varying amplitude is obtained using a relativistic two-fluid model. Based on this nonlinear equation and taking into account some nonlinear phenomena such as modulational instability, self-focusing and soliton formation are investigated. Effect of the magnetized plasma with superthermal ions and mixed nonthermal high-energy tail electrons on these phenomena is considered. It is shown that the nonthermality and superthermality of particles can substantially change the nonlinearity of medium.

  10. X-ray magnetic circular dichroism in d and f ferromagnetic materials: recent theoretical progress. Part II (Review Article)

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.; Shpak, A. P.; Yaresko, A. N.

    2008-02-01

    The present state of theoretical understanding of the x-ray magnetic circular dichroism (XMCD) of 4f and 5f compounds is reviewed. Energy band theory based upon the local spin-density approximation (LSDA) describes the XMCD spectra of transition metal compounds with high accuracy. However, the LSDA does not suffice for lanthanide compounds which have a correlated 4f shell. A satisfactory description of the XMCD spectra could be obtained by using a generalization of the LSDA, in which explicitly f electron Coulomb correlations are taken into account (LSDA +U approach). As examples of this group we consider the compound GdN. We also consider uranium 5f compounds. In those compounds where the 5f electrons are rather delocalized, the LSDA describes the XMCD spectra reasonably well. As an example of this group we consider UFe2. Particular differences occur for uranium compounds in which the 5f electrons are neither delocalized nor localized, but more or less semilocalized. Typical examples are UXAl (X =Co, Rh, and Pt), and UX (X =S, Se, Te). However, the semilocalized 5f's are not inert, but their interaction with conduction electrons plays an important role. We also consider the electronic structure and XMCD spectra of the heavy-fermion compounds UPt3, URu2Si2, UPd2Al3, UNi2Al3, and UBe13, where the degree of the 5f localization is increased in comparison with other uranium compounds. The electronic structure and XMCD spectra of UGe2 which possesses simultaneously ferromagnetism and superconductivity also presented. Recently achieved improvements for describing 5f compounds are discussed.

  11. Effect of collisions on dc magnetic-field generation in a plasma by resonance absorption of light

    SciTech Connect

    Adam, J.C.; Gourdin-Serveniere, A.; Mora, P.; Pellat, R.

    1982-05-01

    The importance of collisional ponderomotive effects on dc magnetic field generation is stressed. Computer simulations show that a weak rate of collision is sufficient to completely modify dc magnetic field generation in the resonant absorption of light, as compared with previous collisionless simulations. The agreement with theoretical predictions is shown.

  12. Magnetic field strength at the innermost circular orbit in accretion disk of supermassive black hole in active galactic nuclei: comparison with the equipartition value

    NASA Astrophysics Data System (ADS)

    Piotrovich, M. Y.; Buliga, S. D.; Gnedin, Y. N.; Natsvlishvili, T. M.; Silant'ev, N. A.

    2015-06-01

    In this paper we present the results of the determination of the magnetic field strength at the innermost stable circular orbit (ISCO) of an active galactic nuclei (AGN) derived from the polarimetric data for radiation emerging from broad line regions (BLR). These results are obtained by the radiative transfer method that takes into account the effect of Faraday rotation depolarization. The observed polarization degree allows to estimate the value of the magnetic field in the BLR and then to derive the ISCO magnetic field strength using the standard accretion disk model (Shakura and Sunyaev in Astron. Astrophys. 24:337, 1973). We used the polarimetric data obtained by Smith et al. (Mon. Not. R. Astron. Soc. 335:773, 2002) to calculate the values of relativistic jet kinetic power of AGN from the derived values of the magnetic field strength at the ISCO radius.

  13. N-Acetyl-L-alanine N'-methylamide: a density functional analysis of the vibrational absorption and vibrational circular dichroism spectra

    NASA Astrophysics Data System (ADS)

    Jalkanen, K. J.; Suhai, S.

    1996-07-01

    Ab initio 6-31G ∗ Becke 3LYP DFT optimized geometries, vibrational frequencies, vibrational absorption (VA) intensities and vibrational circular dichroism (VCD) intensities have been calculated for the eight low energy conformers of N-acetyl-L-alanine N'-methylamide (L-AANMA) in the gas phase and one conformer stabilized by the addition of four water molecules. The VA and VCD spectra are calculated with the 6-31G ∗ Becke 3LYP force fields (Hessians) and atomic polar tensors (APT); 6-31G ∗∗ RHF atomic axial tensors (AAT) for the eight gas phase structures and 6-31G ∗/6-31G RHF AAT for the L-AANMA-water complex. The VA and VCD spectra are also calculated using the 6-31G ∗ Becke 3LYP Hessians; 6-31G ∗∗ RHF APT and AAT for the eight gas phase structures and 6-31G ∗/6-31G RHF APT and AAT for the L-AANMA-water complex. The rotational strengths of the amide A, I, II, III, IV, V and VI modes found in proteins as a function of φ and ψ (for various secondary structures) are for the first time reported for an inherently optically active molecule (non-glycine model) using the 6-31G ∗∗ and 6-31G ∗/6-31G RHF DOG AAT and 6-31G ∗ Becke 3LYP Hessians and APT. This is also the first reported VCD calculation of a molecule with the solvent present. The molecule is not completely solvated, but the important hydrogen-bonded interactions are present and the feasibility of the calculation of the Hessian, APT and AAT with solvent molecules present is demonstrated. The VA and VCD spectra are compared to the experimental VA and VCD spectra in the literature and the conformational analysis (CA) and vibrational assignment of L-AANMA are reinvestigated. The rotational strengths of the amide modes for the various conformers are also compared to peptide and protein VCD spectra of molecules with known secondary structures. The agreement between the calculated rotational strengths of the various amide modes for which experimental measurements have been made is very good

  14. Microwave absorption in the singlet paramagnet HoVO 4 in high pulsed magnetic fields up to 40 T

    NASA Astrophysics Data System (ADS)

    Goiran, M.; Klingeler, R.; Kazei, Z. A.; Snegirev, V. V.

    2007-11-01

    Microwave absorption of the rare-earth (RE) oxide compound HoVO 4 (tetragonal-zircon structure) is investigated in pulsed magnetic fields up to 40 T in the low-temperature range. For a magnetic field along the tetragonal crystal axis a few resonance absorption lines are observed at the wavelengths 871, 406 and 305 μm corresponding to electron transitions from the ground and low-lying energy levels of the Ho 3+ ion. In addition, broad non-resonance absorption is observed at 871 and 406 μm in fields up to 15 T. The positions and intensities of the observed resonance lines are described quite well within the crystal field formalism with the known crystal field parameters. The effects of the small orthorhombic component of the crystal field, magnetic field misorientation out the symmetry axis and various pair interactions on the absorption spectra in HoVO 4 are analyzed and discussed.

  15. Change in the absorption spectra of blood exposed to a low-frequency magnetic field

    NASA Astrophysics Data System (ADS)

    Zalesskaya, G. A.; Mit'kovskaya, N. P.; Galai, O. A.; Kuchinskii, A. V.; Laskina, O. V.

    2007-03-01

    We have used the absorption spectra of whole blood in the UV-visible and IR regions of the spectrum to study changes in the structure of the molecular components of blood when exposed to a low-frequency pulsed magnetic field used to treat ischemic heart disease. We show that pronounced changes in the spectra when the blood is directly exposed in vivo to a magnetic field may be due to breaking of the bond between the heme group and the protein of the hemoglobin, as a consequence of changes in the intermolecular interactions in the polypeptide chains of the hemoglobin and also the spin states of the paramagnetic heme components. Exposure to a magnetic field results in changes in the conformations of the polypeptide chains of hemoglobin and the rate of dissociation of oxyhemoglobin. The structural changes in the hemoglobin molecule are considered as one of the possible primary mechanisms of action on blood in vivo for a low-frequency pulsed magnetic field.

  16. Facile preparation and characterization of modified magnetic silica nanocomposite particles for oil absorption

    NASA Astrophysics Data System (ADS)

    Yu, Liuhua; Hao, Gazi; Liang, Qianqian; Zhou, Shuai; Zhang, Ning; Jiang, Wei

    2015-12-01

    In this study, a novel environmental-friendly and superhydrophobic oil absorbent was fabricated by modifying magnetic silica nanocomposites. It was demonstrated that the modified rough magnetic silica nanocomposite particles possessed a number of superior features such as superhydrophobicity, superoleophilicity, and high oil-water separation efficiency etc. Moreover, the as-obtained material could be used as excellent absorbents for high density oils such as toluene and many organic liquids including viscous oils e.g. lubricating oil. The lubricating oil intake capacity for the nanocomposites was 7.15 times of its own weight. Importantly, the oil-absorption process of the nanocomposites was selective, fast and efficient when they were used in the purification of oil-contaminated water. Notably, the oil-absorbed nanocomposites could be renewed after suitable absolute ethanol washing and natural drying. In addition, the renewed nanocomposites still remained high oil-absorption capacity after the 20th cycle. These inspiring results show that the oil-absorbent material has good prospects for selection removal of oils and organic solvents on water surface. It is believed that the present work may have provided a novel and facile way for preparing environmental-friendly materials with ideal properties.

  17. Electromagnetic wave absorption properties of composites with ultrafine hollow magnetic fibers

    NASA Astrophysics Data System (ADS)

    Yi, Jin Woo; Lee, Sang Bok; Kim, Jin Bong; Lee, Sang Kwan; Park, O. Ok

    2014-06-01

    Ultrafine hollow magnetic fibers were prepared by electroless plating using hydrolyzed polyester fiber as a sacrificial substrate. These hollow fibers can be served for lightweight and efficient electromagnetic (EM) absorbing materials. As observed from SEM and EDS analysis, hollow structures consisting of Ni inner layer and Fe or Fe-Co outer layer were obtained. By introducing Co onto Fe, oxidation of the Fe layer was successfully prevented making it possible to enhance the complex permeability compared to a case in which only Fe was used. Polymeric composites containing the hollow fibers with different weight fractions and fiber lengths were prepared by a simple mixing process. The electromagnetic wave properties of the composites were measured by a vector network analyzer and it was found that the hollow magnetic fibers show a clear resonance peak of the complex permittivity around the X-band range (8-12 GHz) and the resonance frequency strongly depends on the fiber concentration and length. A possible explanation for the unique resonance is that the hollow fibers possess relatively low electrical conductivity and a long mean free path due to their oxidized phase and hollow structure. The calculated EM wave absorption with the measured EM wave properties showed that the composite containing 30 wt% hollow Ni/Fe-Co (7:3) fibers in length of 180 μm exhibited multiple absorbance peaks resulting in a broad absorption bandwidth of 4.2 GHz. It is obvious that this multiple absorbance is attributed to the resonance characteristic of the composite.

  18. Magneto-electric control of magnetization in a chain of circular nanomagnets as new paradigm for ultra low power binary information propagation

    NASA Astrophysics Data System (ADS)

    Salehi-Fashami, Mohammad; Al-Rashid, Mamun; Sun, Wei-Yang; Nordeen, Paul; Bandyopadhyay, Supriyo; Carman, Gregory; Atulasimha, Jayasimha

    Elliptical nanomagnets with bi stable magnetization states are traditionally employed for dipole coupled Bennett clocked nanomagnetic logic.Logic bits are propagated down a chain of nanomagnets by sequentially rotating their magnetizations with an electric field.In this talk,we present for the first time,the notion of replacing elliptical nanomagnets with circular nanomagnets that have no inherent shape anisotropy.The circular nanomagnets would develop bi stable magnetization orientations with the application of an electrical field to induce in-plane strain anisotropy.This new strategy provides two significant advantages for nanomagnetic logic applications:(i)re-orienting the magnetizations does not require overcoming a shape-anisotropy energy barrier and hence the electric field needed to reorient is reduced,leading to lower energy dissipation in the clocking process,and(ii)scalability to dimensions substantially smaller than what presently exists becomes possible. This work was supported by NSF CAREER grant CCF-1253370 and by FAME,one of six centers of STARnet,Semiconductor Research Corporation program sponsored by MARCO and DARPA.

  19. Magnetic-dipolar-mode Fano resonances for microwave spectroscopy of high absorption matter

    NASA Astrophysics Data System (ADS)

    Vaisman, G.; Kamenetskii, E. O.; Shavit, R.

    2015-03-01

    The interaction between high absorption matter and microwave radiated energy is a subject of great importance. In particular, this concerns the microwave spectroscopic characterization of biological liquids. The use of effective testing methods to obtain information about physical properties of different liquids on the molecular level is one of the most important problems in biophysics. However, the standard methods based on microwave resonant techniques are not sufficiently suitable for biological liquids because the resonance peak in a resonator with high-loss liquids is so broad that the material parameters cannot be measured correctly. Although molecular vibrations of biomolecules may have microwave frequencies, it is not thought that such resonant coupling is significant due to their low energy compared with thermal energy and the strongly dampening aqueous environment. This paper presents an innovative microwave sensing technique for different types of lossy materials, including biological liquids. The technique is based on the combination of the microwave perturbation method and the Fano resonance effects observed recently in microwave structures with embedded magnetic-dipolar quantum dots. When the frequency of the magnetic dipolar mode (MDM) resonance is not equal to the cavity resonance frequency, one gets Fano transmission intensity. When the MDM resonance frequency is tuned to the cavity resonance frequency, by a bias magnetic field, one observes a Lorentzian line shape. Use of an extremely narrow Lorentzian peak allows exact probing of the resonant frequency of a cavity loaded by a highly lossy material sample. For different kinds of samples, one has different frequencies of Lorentzian peaks. This presents a picture of precise spectroscopic characterization of high absorption matter in microwaves.

  20. Electronic and magnetic properties of off-stoichiometric Co{sub 2}Mn{sub β}Si/MgO interfaces studied by x-ray magnetic circular dichroism

    SciTech Connect

    Singh, V. R.; Verma, V. K.; Ishigami, K.; Shibata, G.; Fujimori, A.; Koide, T.; Miura, Y.; Shirai, M.; Ishikawa, T.; Li, G.-F.; Yamamoto, M.

    2015-05-28

    We have studied the electronic and magnetic states of Co and Mn atoms at the interface of the Co{sub 2}Mn{sub β}Si (CMS)/MgO (β = 0.69, 0.99, 1.15, and 1.29) magnetic tunnel junction (MTJ) by means of x-ray magnetic circular dichroism. In particular, the Mn composition (β) dependences of the Mn and Co magnetic moments were investigated. The experimental spin magnetic moments of Mn, m{sub spin}(Mn), derived from x-ray magnetic circular dichroism weakly decreased with increasing Mn composition β in going from Mn-deficient to Mn-rich CMS films. This behavior was explained by first-principles calculations based on the antisite-based site-specific formula unit (SSFU) composition model, which assumes the formation of only antisite defect, not vacancies, to accommodate off-stoichiometry. Furthermore, the experimental spin magnetic moments of Co, m{sub spin}(Co), also weakly decreased with increasing Mn composition. This behavior was consistently explained by the antisite-based SSFU model, in particular, by the decrease in the concentration of Co{sub Mn} antisites detrimental to the half-metallicity of CMS with increasing β. This finding is consistent with the higher tunnel magnetoresistance ratios which have been observed for CMS/MgO/CMS MTJs with Mn-rich CMS electrodes.

  1. Magnetic circular dichroism studies of myoglobin, hemoglobin and peroxidase at room and low temperatures. Ferrous high spin derivatives.

    PubMed

    Sharonov, Y A; Mineyev, A P; Livshitz, M A; Sharonova, N A; Zhurkin, V B; Lysov, Y P

    1978-04-13

    The magnetic circular dichroism spectra (MCD) recorded for the visible and near-UV regions of high-spin ferrous derivatives of myoglobin, hemoglobin, hemoglobin dimers and isolated chains as well as of horseradish peroxidase at pH 6.8 and 11.4 have been compared at the room and liquid nitrogen temperatures. The MCD of the Q00- and QV-bands have been shown to be sensitive to structural differences in the heme environment of these hemoproteins. The room temperature visible MCD of native hemoglobin differs from that of myoglobin, hemoglobin dimers and isolated chains as well as from that of model pentacoordinated complex. The MCD of hemoglobin is characterized by the greater value of the MCD intensity ratio of derivative shape A-term in the Q00-band to the A-term in the QV-band. The evidneces are presented for the existence of two pH-dependent forms of ferroperoxidase, the neutral peroxidase shows the "hemoglobin-like" MCD, while the alkaline ferroperoxidase is characterized by the "myoglobin-like" MCD spectrum in the visible region. The differences in the MCD of deoxyhemoglobin and neutral ferroperoxidase as compared with other high-spin ferrous hemoproteins are considered to result from the constraints on heme group imposed by quaternary and/or tertiary protein structure. The differences between hemoporteins which are seen at the room temperature become more pronounced at liquid nitrogen temperature. Except the peak at approximately 580 nm in the MCD of deoxymyoglobin and reduced peroxidase at pH 11.4 the visible MCD does not show appreciable temperature dependent C-terms. The nature of the temperature dependent effect at approximately 580 nm is not clear. The Soret MCD of all hemoproteins studied are similar and are predominantly composed of the derivative-shaped C-terms as revealed by the increase of the MCD peaks approximately in accordance with Boltzmann distribution. The interpretation of temperature-dependent MCD observed for the Soret band has been made in

  2. The magnetic circular dichroism spectra of the linear trinuclear clusters [Fe 3S 4(SR) 4] 3- in purple aconitase and in a synthetic model

    NASA Astrophysics Data System (ADS)

    Richards, A. J. M.; Thomson, A. J.; Holm, R. H.; Hagen, K. S.

    The low-temperature magnetic circular dichroism (MCD) spectra and MCD magnetization properties of the linear three-iron cluster [Fe(μ 2-S) 2Fe(μ 2-S) 2Fe] + have been compared in a solution of the model compound (Et 4N) 3[Fe 3S 4(SEt) 4] and in the "purple" form of beef heart aconitase. The similarity between the spectra confirms the close equivalence of the structures in the model and the protein. Analysis of the MCD magnetization curves has been carried out in terms of a ground state spin S = 5/2 and E / D values of 0.33 (model) and 0.31 (aconitase) established from the electron paramagnetic resonance (EPR) spectra. This gives estimates of the axial zero-field splitting parameters D = +0.7 ± 0.2 cm -1 and +1.5 ± 0.2 cm -1 for the model and protein, respectively.

  3. Magnetic Turbulence and Line Broadening in Simulations of Lyman-Alpha Absorption

    NASA Astrophysics Data System (ADS)

    Gurvich, Alex; Burkhart, Blakesley K.; Bird, Simeon

    2016-01-01

    We use the Illustris cosmological AREPO simulations to study the effects of gas turbulence and magnetic fields on measurements from the Lyman-Alpha forest. We generate simulated Lyman-Alpha spectra and plot the distributions of Column Density (CDD) and Doppler Width (b) both by adhering to the canonical method of fitting Voigt profiles to absorption lines and by directly measuring the column density and equivalent widths from snapshot data .We investigate the effects of additional unresolved gas turbulence in Illustris by adding an additional broadening term to the line profiles to mimic turbulent broadening. When we do this, we find a measurable effect in the CDD and an offset in the mean of the b distribution corresponding to the additional turbulence. We also compare different MHD runs in AREPO we find that the CDD can measurably differentiate between magnetic seed field at redshifts as low as z=0.1, but we do not find that the b distribution is affected at a detectable level. Our work suggests that the effects of turbulence and magnetic fields from z=2-0.1 can potentially be measured with these diagnostics. This work was supported in part by the NSF REU and DoD ASSURE programs under NSF grant no. 1262851 and by the Smithsonian Institution.

  4. On the reliable measurement of specific absorption rates and intrinsic loss parameters in magnetic hyperthermia materials

    NASA Astrophysics Data System (ADS)

    Wildeboer, R. R.; Southern, P.; Pankhurst, Q. A.

    2014-12-01

    In the clinical application of magnetic hyperthermia, the heat generated by magnetic nanoparticles in an alternating magnetic field is used as a cancer treatment. The heating ability of the particles is quantified by the specific absorption rate (SAR), an extrinsic parameter based on the clinical response characteristic of power delivered per unit mass, and by the intrinsic loss parameter (ILP), an intrinsic parameter based on the heating capacity of the material. Even though both the SAR and ILP are widely used as comparative design parameters, they are almost always measured in non-adiabatic systems that make accurate measurements difficult. We present here the results of a systematic review of measurement methods for both SAR and ILP, leading to recommendations for a standardised, simple and reliable method for measurements using non-adiabatic systems. In a representative survey of 50 retrieved datasets taken from published papers, the derived SAR or ILP was found to be more than 5% overestimated in 24% of cases and more than 5% underestimated in 52% of cases.

  5. Absorption and Circular Dichroism Spectra of La{sub 3}Ga{sub 5}SiO{sub 14} Crystals Doped with Pr{sup 3+}, Ho{sup 3+}, and Er{sup 3+} Ions

    SciTech Connect

    Burkov, V. I.; Lysenko, O. A.; Mill, B. V.

    2010-11-15

    The absorption and circular dichroism (CD) spectra of La{sub 3}Ga{sub 5}SiO{sub 14} langasite crystals doped with Pr{sup 3+}, Ho{sup 3+}, and Er{sup 3+} ions have been studied in the wavelength range of 350-700 nm. The electronic transitions of these ions, which replace La3+ ions in the 3e position with the symmetry 2, are observed in the spectra. All transitions are active in both the absorption and CD spectra. The dipole strengths D{sub om}, rotational strengths R{sub om}, and anisotropy factors g have been calculated for well-resolved bands. Some features are noted for the spectra that were obtained, and their relationship with the structure disorder is considered.

  6. Circular dichroism of chiral photonic crystal liquid layers with enclosed defect inside

    NASA Astrophysics Data System (ADS)

    Gevorgyan, Ashot; Kocharian, Armen; Vardanyan, Gagik

    2015-03-01

    The photonic crystals of artificial and self-organizing structures with spatial periodic changes in dielectric and magnetic properties have attracted considerable interest recently due to unusual physical properties and wide practical applications. The chiral periodic structure in the scale of optical wavelength gives rise to strong and characteristic circular dichroism responses at visible wavelengths. Here we investigate photonic density, circular dichroism and peculiarities of absorption and emission spectra at various eigen polarizations in multilayered one-dimensional chiral soft matter with two layers of CLCs and an isotropic defect layer inside. The circular dichroism is defined by differences in light energy absorption A=1-(R + T) by the system (R and T are the reflection and transmission coefficients, respectively) and A s , r are the light absorptions, if the incident light has left and right circular polarizations, respectively. This problem can be solved by the modified Ambartsumian's layer addition method. The influence of absorption and gain on the circular dichroism, absorption and emission spectra is established in cholesteric liquid crystal (CLC) cell with an isotropic defect layer inside.

  7. The right circular polarized waves in the three-dimensional anisotropic dispersive photonic crystals consisting of the magnetized plasma and uniaxial material as the Faraday effects considered

    SciTech Connect

    Zhang, Hai-Feng E-mail: lsb@nuaa.edu.cn; Liu, Shao-Bin E-mail: lsb@nuaa.edu.cn; Tang, Yi-Jun; Zhen, Jian-Ping

    2014-03-15

    In this paper, the properties of the right circular polarized (RCP) waves in the three-dimensional (3D) dispersive photonic crystals (PCs) consisting of the magnetized plasma and uniaxial material with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, which the homogeneous anisotropic dielectric spheres (the uniaxial material) immersed in the magnetized plasma background, as the Faraday effects of magnetized plasma are considered (the incidence electromagnetic wave vector is parallel to the external magnetic field at any time). The equations for calculating the anisotropic photonic band gaps (PBGs) for the RCP waves in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, anisotropic dielectric filling factor, plasma frequency, and plasma cyclotron frequency (the external magnetic field) on the properties of first two anisotropic PBGs for the RCP waves are investigated in detail, respectively. The numerical results show that the anisotropy can open partial band gaps in fcc lattices at U and W points, and the complete PBGs for the RCP waves can be achieved compared to the conventional 3D dispersive PCs composed of the magnetized plasma and isotropic material. It is also shown that the first two anisotropic PBGs can be tuned by those parameters as mentioned above. Those PBGs can be enlarged by introducing the uniaxial material into such 3D PCs as the Faraday effects are considered.

  8. Quantum Switching of Magnetic Fields by Circularly Polarized Re-Optimized π Laser Pulses: From One-Electron Atomic Ions to Molecules

    NASA Astrophysics Data System (ADS)

    Barth, Ingo; Manz, Jörn

    Circularly polarized re-optimized π laser pulses may induce electronic and/or nuclear ring currents in model systems, from one-electron atomic ions till molecules which should have three-, four-, or higher-fold axes of rotations or reflection-rotations, in order to support doubly or more degenerate, complex-valued eigenstates which support these ring currents. The ring currents in turn induce magnetic fields. The effects are about two orders of magnitude larger than for traditional ring currents which are induced by external magnetic fields. Moreover, the laser pulses allow to control the strengths and shapes of the ring currents and, therefore, also the induced magnetic fields. We present a survey of the development of the field, together with new quantum simulations which document ultrafast switchings of magnetic fields. We discuss various criteria such as strong ring currents with small radii, in order to generate huge magnetic fields, approaching 1,000T, in accord with the Biot-Savart law. Moreover, we consider various methods for monitoring the fields, and for applications, in particular ultrafast deflections of neutrons by means of quantum switching of the ring currents and induced magnetic fields.

  9. The right circular polarized waves in the three-dimensional anisotropic dispersive photonic crystals consisting of the magnetized plasma and uniaxial material as the Faraday effects considered

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Zhen, Jian-Ping; Tang, Yi-Jun

    2014-03-01

    In this paper, the properties of the right circular polarized (RCP) waves in the three-dimensional (3D) dispersive photonic crystals (PCs) consisting of the magnetized plasma and uniaxial material with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, which the homogeneous anisotropic dielectric spheres (the uniaxial material) immersed in the magnetized plasma background, as the Faraday effects of magnetized plasma are considered (the incidence electromagnetic wave vector is parallel to the external magnetic field at any time). The equations for calculating the anisotropic photonic band gaps (PBGs) for the RCP waves in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, anisotropic dielectric filling factor, plasma frequency, and plasma cyclotron frequency (the external magnetic field) on the properties of first two anisotropic PBGs for the RCP waves are investigated in detail, respectively. The numerical results show that the anisotropy can open partial band gaps in fcc lattices at U and W points, and the complete PBGs for the RCP waves can be achieved compared to the conventional 3D dispersive PCs composed of the magnetized plasma and isotropic material. It is also shown that the first two anisotropic PBGs can be tuned by those parameters as mentioned above. Those PBGs can be enlarged by introducing the uniaxial material into such 3D PCs as the Faraday effects are considered.

  10. Measurement of the transmission magnetic circular dichroism of Ga1-xMnxAs epilayers using a built-in p-i-n photodiode

    NASA Astrophysics Data System (ADS)

    He, Z. X.; Zheng, H. Z.; Wang, H. L.; Zhao, J. H.

    2014-02-01

    By constructing a GaMnAs epilayer/semi-insulating In0.2Ga0.8As/(001) n+-GaAs substrate layer structure as a built-in p-i-n photodiode, we developed a scheme for on-chip measurements of transmission magnetic circular dichroism (T-MCD). Both the hysteresis loops in the magnetic field sweeps and the wavelength scans at saturated magnetic fields measured using the new T-MCD scheme, illustrated the same features as those previously measured on the freestanding GaMnAs thin films by conventional T-MCD. Because a large group of epitaxially grown magnetic film/semiconductor heterostructures, such as Fe, NiFe, CoFeAl, and MnGa films on semiconductor substrates, are becoming important new building blocks for semiconductor-based spin field-effect transistor, perpendicular magnetic tunnel junction (p-MTJ) and lateral MTJ devices, the new T-MCD scheme can be applied to tests of their magnetic properties by forming either p-i-n or Schottky photodiodes.

  11. Measuring magnetisation reversal in micron-sized Nd2Fe14B single crystals by microbeam x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Sugawara, Akira; Ueda, Kazuhiro; Nakayama, T.; Lee, N.; Yamamoto, H.

    2016-10-01

    Magnetisation reversal of micron-sized Nd2Fe14B single crystals with magnetisation as weak as 10-9 emu (1 µm size) was studied. Single-crystal specimens (cylinders with diameter and height of 1 to 6 µm) were prepared by focused-ion beam so that both the magnetic easy and hard axes were included in the basal plane. Their magnetic hysteresis loops were measured when they were rotated with respect to the cylindrical axis by using microbeam hard-x-ray magnetic circular dichroism (XMCD) under transmission geometry. It was found that coercivity is inversely proportional to the cosine of the angle between the magnetocrystalline easy axis and magnetic-field direction and that the magnetisation reversal is dominated by domain-wall pinning in two different modes. One is related to penetration of the reversed domain nucleated in a subsurface soft layer into the bulk hard phase, of which the hysteresis loops exhibit a single-stage abrupt jump in magnetization. The other mode is pinning of the walls within the bulk grain, of which the hysteresis loops exhibit a plateau. The multi-domain structure associated with the pinning was confirmed by XMCD mapping. The proposed method fills the gap between conventional bulk magnetic measurement and submicron-scale electrical-transport measurement for nanofabricated thin films and/or fine particles. It is expected to provide new insights into elemental magnetisation processes in micron-scale regions.

  12. RESULTS OF STRETCHED WIRE FIELD INTEGRAL MEASUREMENTS ON THE MINI-UNDULATOR MAGNET-COMPARISON OF RESULTS OBTAINED FROM CIRCULAR AND TRANSLATIONAL MOTION OF THE INTEGRATING WIRE.

    SciTech Connect

    SOLOMON, L.

    1998-05-01

    Measurements of the multipole content of the Mini-Undulator magnet have been made with two different integrating wire techniques. Both measurements used 43 strand Litz wire stretched along the length of the magnet within the magnet gap. In the first technique, the wire motion was purely translational, while in the second technique the wire was moved along a circular path. The induced voltage in the Litz wire was input into a Walker integrator, and the integrator output was analyzed as a function of wire position for determination of the multipole content of the magnetic field. The mini-undulator magnet is a 10 period, 80 mm per period hybrid insertion device. For all the data contained herein the magnet gap was set at 49 mm. In the mini-undulator magnet, the iron poles are 18mm x 32mm x 86mm, and the Samarium Cobalt permanent magnet blocks are 22mm x 21mm x 110mm. For this magnet, which is a shortened prototype for the NSLS Soft X-Ray Undulator Magnet, the undulator parameter K = 0.934 B(Tesla){lambda}(cm), and B(tesla) = 0.534/sinh({pi}Gap/{lambda}). At a gap of 49 mm, the magnetic field is 1590 Gauss. The 43 strand Litz wire is supported on motorized x-y stages at both ends of the magnet, which are controlled by stepping motors through a Labview program. One leg of the wire loop is within the magnet gap, and the other leg is in an essentially field free region. Only the leg of the wire loop within the magnet gap is moved during data acquisition. The Litz wire is tensioned with 11.5 pounds, and is wrapped with a supporting tape which is itself tensioned with 18 pounds through a spring and turnbuckle arrangement. With this setup the sag in the wire over the 72 inch span is less than 0.003 inches, as measured with survey instruments. Photographs of the setup are shown.

  13. Orbital and spin moments of 5 to 11 nm Fe{sub 3}O{sub 4} nanoparticles measured via x-ray magnetic circular dichroism

    SciTech Connect

    Cai, Y. P.; Chesnel, K. Trevino, M.; Westover, A.; Turley, S.; Harrison, R. G.; Hancock, J. M.; Scherz, A.; Reid, A.; Wu, B.; Graves, C.; Wang, T.; Liu, T.; Dürr, H.

    2014-05-07

    The orbital and spin contributions to the magnetic moment of Fe in Fe{sub 3}O{sub 4} nanoparticles were measured using X-ray magnetic circular dichroism (XMCD). Nanoparticles of different sizes, ranging from 5 to 11 nm, were fabricated via organic methods and their magnetic behavior was characterized by vibrating sample magnetometry (VSM). An XMCD signal was measured for three different samples at 300 K and 80 K. The extracted values for the orbital and spin contributions to the magnetic moment showed a quenching of the orbital moment and a large spin moment. The calculated spin moments appear somewhat reduced compared to the value expected for bulk Fe{sub 3}O{sub 4}. The spin moments measured at 80 K are larger than at 300 K for all the samples, revealing significant thermal fluctuations effects in the nanoparticle assemblies. The measured spin moment is reduced for the smallest nanoparticles, suggesting that the magnetic properties of Fe{sub 3}O{sub 4} nanoparticles could be altered when their size reaches a few nanometers.

  14. Dependency of magnetic microwave absorption on surface architecture of Co20Ni80 hierarchical structures studied by electron holography

    NASA Astrophysics Data System (ADS)

    Liu, Qinhe; Xu, Xianhui; Xia, Weixing; Che, Renchao; Chen, Chen; Cao, Qi; He, Jingang

    2015-01-01

    To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a series of Co20Ni80 hierarchical structures with different surface morphologies, including flower-, urchin-, ball-, and chain-like morphologies, were obtained using structure-directing templates via a facile one-step solvothermal treatment. The microwave reflection loss (RL) of urchin-like Co20Ni80 hierarchical structures reaches as high as -33.5 dB at 3 GHz, with almost twice the RL intensity of the ball- and chain-like structures, and the absorption bandwidth (<-10 dB) is about 5.5 GHz for the flower-like morphology, indicating that the surface nanospikes and nanoflakes on the Co20Ni80 microsphere surfaces have great influences on their magnetic microwave absorption properties. Electron holography analysis reveals that the surface nanospikes and nanoflakes could generate a high density of stray magnetic flux lines and contribute a large saturation magnetization (105.62 emu g-1 for urchin-like and 96.41 emu g-1 for flower-like morphology), leading the urchin-like and flower-like Co20Ni80 to possess stronger microwave RL compared with the ball-like and chain-like Co20Ni80 alloys. The eddy-current absorption mechanism μ''(μ')-2(f)-1 is dominant in the frequency region above 8 GHz, implying that eddy-current loss is a vital factor for microwave RL in the high frequency range. It can be supposed from our findings that different surface morphologies of magnetic hierarchical structures might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a

  15. Wireless charing pillow for a fully implantable hearing aid: Design of a circular array coil based on finite element analysis for reducing magnetic weak zones.

    PubMed

    Lim, Hyung-Gyu; Kim, Jong Hoon; Shin, Dong Ho; Woo, Seong Tak; Seong, Ki Woong; Lee, Jyung Hyun; Kim, Myoung Nam; Wei, Qun; Cho, Jin-Ho

    2015-01-01

    Many types of fully implantable hearing aids have been developed. Most of these devices are implanted behind the ear. To maintain the implanted device for a long period of time, a rechargeable battery and wireless power transmission are used. Because inductive coupling is the most renowned method for wireless power transmission, many types of fully implantable hearing aids are transcutaneously powered using inductively coupled coils. Some patients with an implantable hearing aid require a method for conveniently charging their hearing aid while they are resting or sleeping. To address this need, a wireless charging pillow has been developed that employs a circular array coil as one of its primary parts. In this device, all primary coils are simultaneously driven to maintain an effective charging area regardless of head motion. In this case, however, there may be a magnetic weak zone that cannot be charged at the specific secondary coil's location on the array coil. In this study, assuming that a maximum charging distance is 4 cm, a circular array coil-serving as a primary part of the charging pillow-was designed using finite element analysis. Based on experimental results, the proposed device can charge an implantable hearing aid without a magnetic weak zone within 4 cm of the perpendicular distance between the primary and secondary coils. PMID:26405942

  16. Wireless charing pillow for a fully implantable hearing aid: Design of a circular array coil based on finite element analysis for reducing magnetic weak zones.

    PubMed

    Lim, Hyung-Gyu; Kim, Jong Hoon; Shin, Dong Ho; Woo, Seong Tak; Seong, Ki Woong; Lee, Jyung Hyun; Kim, Myoung Nam; Wei, Qun; Cho, Jin-Ho

    2015-01-01

    Many types of fully implantable hearing aids have been developed. Most of these devices are implanted behind the ear. To maintain the implanted device for a long period of time, a rechargeable battery and wireless power transmission are used. Because inductive coupling is the most renowned method for wireless power transmission, many types of fully implantable hearing aids are transcutaneously powered using inductively coupled coils. Some patients with an implantable hearing aid require a method for conveniently charging their hearing aid while they are resting or sleeping. To address this need, a wireless charging pillow has been developed that employs a circular array coil as one of its primary parts. In this device, all primary coils are simultaneously driven to maintain an effective charging area regardless of head motion. In this case, however, there may be a magnetic weak zone that cannot be charged at the specific secondary coil's location on the array coil. In this study, assuming that a maximum charging distance is 4 cm, a circular array coil-serving as a primary part of the charging pillow-was designed using finite element analysis. Based on experimental results, the proposed device can charge an implantable hearing aid without a magnetic weak zone within 4 cm of the perpendicular distance between the primary and secondary coils.

  17. Low frequency absorption properties of a thin metamaterial absorber with cross-array on the surface of a magnetic substrate

    NASA Astrophysics Data System (ADS)

    Chen, Qian; Bie, Shaowei; Yuan, Wei; Xu, Yongshun; Xu, Haibing; Jiang, Jianjun

    2016-10-01

    The design, fabrication, and measurement of a metamaterial with broadband microwave absorption properties in the low frequency range are presented in this paper. The metamaterial has a layered structure with a thickness of 2.2 mm, and consists of a conventional printed circuit board (PCB) process fabricated cross array on the surface of a flake-shaped carbonyl iron (CI) powder-filled silicon rubber composite magnetic substrate backed by a metal plane. The measurement results indicate that the absorption bandwidth (defined as the frequency range with reflection coefficient below  -10 dB) of the proposed structure is 2.55 GHz-5.68 GHz. The power loss mechanism was outlined according to the current distribution on and off the resonance frequency. Moreover, the absorption performance of the proposed structure for incident angles ranging from 0° to 60° for both transverse electric (TE) wave and transverse magnetic (TM) waves were exhibited.

  18. Controlled cobalt doping in the spinel structure of magnetosome magnetite: new evidences from element- and site-specific X-ray magnetic circular dichroism analyses.

    PubMed

    Li, Jinhua; Menguy, Nicolas; Arrio, Marie-Anne; Sainctavit, Philippe; Juhin, Amélie; Wang, Yinzhao; Chen, Haitao; Bunau, Oana; Otero, Edwige; Ohresser, Philippe; Pan, Yongxin

    2016-08-01

    The biomineralization of magnetite nanocrystals (called magnetosomes) by magnetotactic bacteria (MTB) has attracted intense interest in biology, geology and materials science due to the precise morphology of the particles, the chain-like assembly and their unique magnetic properties. Great efforts have been recently made in producing transition metal-doped magnetosomes with modified magnetic properties for a range of applications. Despite some successful outcomes, the coordination chemistry and magnetism of such metal-doped magnetosomes still remain largely unknown. Here, we present new evidences from X-ray magnetic circular dichroism (XMCD) for element- and site-specific magnetic analyses that cobalt is incorporated in the spinel structure of the magnetosomes within Magnetospirillum magneticum AMB-1 through the replacement of Fe(2+) ions by Co(2+) ions in octahedral (Oh) sites of magnetite. Both XMCD at Fe and Co L2,3 edges, and energy-dispersive X-ray spectroscopy on transmission electron microscopy analyses reveal a heterogeneous distribution of cobalt occurring either in different particles or inside individual particles. Compared with non-doped one, cobalt-doped magnetosome sample has lower Verwey transition temperature and larger magnetic coercivity, related to the amount of doped cobalt. This study also demonstrates that the addition of trace cobalt in the growth medium can significantly improve both the cell growth and the magnetosome formation within M. magneticum AMB-1. Together with the cobalt occupancy within the spinel structure of magnetosomes, this study indicates that MTB may provide a promising biomimetic system for producing chains of metal-doped single-domain magnetite with an appropriate tuning of the magnetic properties for technological and biomedical applications. PMID:27512138

  19. Controlled cobalt doping in the spinel structure of magnetosome magnetite: new evidences from element- and site-specific X-ray magnetic circular dichroism analyses.

    PubMed

    Li, Jinhua; Menguy, Nicolas; Arrio, Marie-Anne; Sainctavit, Philippe; Juhin, Amélie; Wang, Yinzhao; Chen, Haitao; Bunau, Oana; Otero, Edwige; Ohresser, Philippe; Pan, Yongxin

    2016-08-01

    The biomineralization of magnetite nanocrystals (called magnetosomes) by magnetotactic bacteria (MTB) has attracted intense interest in biology, geology and materials science due to the precise morphology of the particles, the chain-like assembly and their unique magnetic properties. Great efforts have been recently made in producing transition metal-doped magnetosomes with modified magnetic properties for a range of applications. Despite some successful outcomes, the coordination chemistry and magnetism of such metal-doped magnetosomes still remain largely unknown. Here, we present new evidences from X-ray magnetic circular dichroism (XMCD) for element- and site-specific magnetic analyses that cobalt is incorporated in the spinel structure of the magnetosomes within Magnetospirillum magneticum AMB-1 through the replacement of Fe(2+) ions by Co(2+) ions in octahedral (Oh) sites of magnetite. Both XMCD at Fe and Co L2,3 edges, and energy-dispersive X-ray spectroscopy on transmission electron microscopy analyses reveal a heterogeneous distribution of cobalt occurring either in different particles or inside individual particles. Compared with non-doped one, cobalt-doped magnetosome sample has lower Verwey transition temperature and larger magnetic coercivity, related to the amount of doped cobalt. This study also demonstrates that the addition of trace cobalt in the growth medium can significantly improve both the cell growth and the magnetosome formation within M. magneticum AMB-1. Together with the cobalt occupancy within the spinel structure of magnetosomes, this study indicates that MTB may provide a promising biomimetic system for producing chains of metal-doped single-domain magnetite with an appropriate tuning of the magnetic properties for technological and biomedical applications.

  20. Circular epidemiology.

    PubMed

    Kuller, L H

    1999-11-01

    Circular epidemiology can be defined as the continuation of specific types of epidemiologic studies beyond the point of reasonable doubt of the true existence of an important association or the absence of such an association. Circular epidemiology is an extreme example of studies of the consistency of associations. A basic problem for epidemiology is the lack of a systematic approach to acquiring new knowledge to reach a goal of improving public health and preventive medicine. For epidemiologists, research support unfortunately is biased toward the continued study of already proven hypotheses. Circular epidemiology, however, freezes at one point in the evolution of epidemiologic studies, failing to move from descriptive to analytical case-control and longitudinal studies, for example, to experimental, clinical trials. Good epidemiology journals are filled with very well-conducted epidemiologic studies that primarily repeat the obvious or are variations on the theme.

  1. Construction of CuS Nanoflakes Vertically Aligned on Magnetically Decorated Graphene and Their Enhanced Microwave Absorption Properties.

    PubMed

    Liu, Panbo; Huang, Ying; Yan, Jing; Yang, Yiwen; Zhao, Yang

    2016-03-01

    Hybrid nanocomposites with enhanced microwave absorption properties have been designed by growing CuS nanoflakes on magnetically decorated graphene, and the effect of special nanostructures on microwave absorption properties has been investigated. The structure of the nanocomposites was characterized by Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), N2 adsorption-desorption, and vibrating sample magnetometer (VSM). The influence of cetyltrimethylammonium bromide (CTAB) on the morphology of CuS nanoflakes was also investigated. A possible formation process of the nanocomposites and the mechanism of microwave absorption were explained in detail. As an absorber, the nanocomposites with a filler loading of 20 wt % exhibited enhanced microwave absorption properties due to the special nanostructures, extra void space, and synergistic effect. The maximum reflection loss can reach -54.5 dB at 11.4 GHz, and the absorption bandwidths exceeding -10 dB are 4.5 GHz with a thickness of 2.5 mm, which can be adjusted by the thickness. The results indicate that the hybrid nanocomposites with enhanced microwave absorption properties and lightweight have a promising future in decreasing electromagnetic wave irradiation.

  2. Electron's anomalous magnetic-moment effects on electron-hydrogen elastic collisions in the presence of a circularly polarized laser field

    SciTech Connect

    Elhandi, S.; Taj, S.; Attaourti, Y.; Manaut, B.; Oufni, L.

    2010-04-15

    The effect of the electron's anomalous magnetic moment on the relativistic electronic dressing for the process of electron-hydrogen atom elastic collisions is investigated. We consider a laser field with circular polarization and various electric field strengths. The Dirac-Volkov states taking into account this anomaly are used to describe the process in the first order of perturbation theory. The correlation between the terms coming from this anomaly and the electric field strength gives rise to the strong dependence of the spinor part of the differential cross section (DCS) with respect to these terms. A detailed study has been devoted to the nonrelativistic regime as well as the moderate relativistic regime. Some aspects of this dependence as well as the dynamical behavior of the DCS in the relativistic regime have been addressed.

  3. Valence-state Model of Strain-dependent Mn L2,3 X-ray Magnetic Circular Dichroism from Ferromagnetic Semiconductors

    SciTech Connect

    van der Laan, G.; Edmonds, K. W.; Arenholz, E.; Farley, N. R. S.; Gallagher, B. L.

    2010-03-30

    We present a valence-state model to explain the characteristics of a recently observed pre-edge feature in Mn L{sub 3} x-ray magnetic circular dichroism (XMCD) of ferromagnetic (Ga,Mn)As and (Al,Ga,Mn)As thin films. The prepeak XMCD shows a uniaxial anisotropy, contrary to the cubic symmetry of the main structures induced by the crystalline electric field. Reversing the strain in the host lattice reverses the sign of the uniaxial anisotropy. With increasing carrier localization, the prepeak height increases, indicating an increasing 3d character of the hybridized holes. Hence, the feature is ascribed to transitions from the Mn 2p core level to unoccupied p-d hybridized valence states. The characteristics of the prepeak are readily reproduced by the model calculation taking into account the symmetry of the strain-, spin-orbit-, and exchange-split valence states around the zone center.

  4. Electric field modulation of magnetic anisotropy and microwave absorption properties in Fe50Ni50/Teflon composite films

    NASA Astrophysics Data System (ADS)

    Xia, Zhenjun; He, Jun; Ou, Xiulong; Wang, Yu; He, Shuli; Zhao, Dongliang; Yu, Guanghua

    2016-05-01

    Fe50Ni50 nanoparticle films with the size about 6 nm were deposited by a high energetic cluster deposition source. An electric field of about 0 - 40 kV was applied on the sample platform when the films were prepared. The field assisted deposition technique can dramatically induce in-plane magnetic anisotropy. To probe the microwave absorption properties, the Fe50Ni50 nanoparticles were deliberately deposited on the dielectric Teflon sheet. Then the laminated Fe50Ni50/Teflon composites were used to do reflection loss scan. The results prove that the application of electric field is an effective avenue to improve the GHz microwave absorption performance of our magnetic nanoparticles films expressed by the movement of reflection loss peak to high GHz region for the composites.

  5. Excellent Electromagnetic Absorption Capability of Ni/Carbon Based Conductive and Magnetic Foams Synthesized via a Green One Pot Route.

    PubMed

    Zhao, Hai-Bo; Fu, Zhi-Bing; Chen, Hong-Bing; Zhong, Ming-Long; Wang, Chao-Yang

    2016-01-20

    Electromagnetic microwave absorption materials have attracted a great deal of attention. Foams for the low density and tunable porosity are considered as ideal microwave absorbents, while with the requirement of improving their inherent electromagnetic properties. In this manuscript, an innovative, easy, and green method was presented to synthesize an electromagnetic functionalized Ni/carbon foam, in which the formation of Ni nanoparticles and carbon occurred simultaneously from an affordable alginate/Ni(2+) foam precursor. The resultant Ni/carbon foam had a low density (0.1 g/cm(-3)) and high Ni nanoparticles loading (42 wt %). These Ni nanoparticles with a diameter of about 50-100 nm were highly crystallized and evenly embedded in porous graphite carbon without aggregation. Also, the resultant foam had a high surface area (451 m(2) g(-1)) and porosity and showed a moderate conductivity (6 S/m) and significant magnetism. Due to these special characteristics, the Ni/carbon foam exhibited greatly enhanced microwave absorption ability. Only with 10 wt % of functional fillers being used in the test template, the Ni/carbon foam based composite could reach an effective absorption bandwidth (below -10 dB) of 4.5 GHz and the minimum reflection value of -45 dB at 13.3 GHz with a thickness of 2 mm, while the traditional carbon foam and nano-Ni powder both showed very weak microwave absorption (the minimum reflection value < -10 dB). This foam was demonstrated to be a lightweight, high performance, and low filler loading microwave absorbing material. Furthermore, the detailed absorption mechanism of the foam was investigated. The result showed that the derived strong dielectric loss, including conductivity loss, interface polarization loss, weak magnetic loss, and naoporosity, contributes a great electromagnetic absorption. PMID:26710881

  6. Investigations of Magnetic Overlayers at the Advanced Photon Source

    SciTech Connect

    Tobin, J G; Yu, S; Butterfield, M T

    2009-06-26

    Magnetic overlayers of Fe and Co have been investigated with X-ray Magnetic Circular Dichroism in X-ray Absorption Spectroscopy (XMCD-ABS) and Photoelectron Spectroscopy (PES), including Spin-Resolved Photoelectron Spectroscopy (SRPES), at Beamline 4 at the Advanced Photon Source (APS). Particular emphasis was placed upon the interrogation of the 2p levels of the Fe.

  7. Investigations of magnetic overlayers at the Advanced Photon Source

    SciTech Connect

    Tobin, J.G.; Yu, S.-W.; Butterfield, M.T.; Komesu, Takashi; Waddill, G.D.

    2010-08-27

    Magnetic overlayers of Fe and Co have been investigated with x-ray magnetic circular dichroism in x-ray absorption spectroscopy and photoelectron spectroscopy, including spin-resolved photoelectron spectroscopy, at Beamline 4 at the Advanced Photon Source. Particular emphasis was placed upon the interrogation of the 2p levels of the Fe.

  8. Magnetic circular dichroism studies of the active site heme coordination sphere of exogenous ligand-free ferric cytochrome c peroxidase from yeast: effects of sample history and pH.

    PubMed

    Pond, A E; Sono, M; Elenkova, E A; McRee, D E; Goodin, D B; English, A M; Dawson, J H

    1999-09-30

    Electronic absorption and magnetic circular dichroism (MCD) spectroscopic data at 4 degrees C are reported for exogenous ligand-free ferric forms of cytochrome c peroxidase (CCP) in comparison with two other histidine-ligated heme proteins, horseradish peroxidase (HRP) and myoglobin (Mb). In particular, we have examined the ferric states of yeast wild-type CCP (YCCP), CCP (MKT) which is the form of the enzyme that is expressed in and purified from E. coli, and contains Met-Lys-Thr (MKT) at the N-terminus, CCP (MKT) in the presence of 60% glycerol, lyophilized YCCP, and alkaline CCP (MKT). The present study demonstrates that, while having similar electronic absorption spectra, the MCD spectra of ligand-free ferric YCCP and CCP (MKT) are somewhat varied from one another. Detailed spectral analyses reveal that the ferric form of YCCP, characterized by a long wavelength charge transfer (CT) band at 645 nm, exists in a predominantly penta-coordinate state with spectral features similar to those of native ferric HRP rather than ferric Mb (His/water hexa-coordinate). The electronic absorption spectrum of ferric CCP (MKT) is similar to those of the penta-coordinate states of ferric YCCP and ferric HRP including a CT band at 645 nm. However, its MCD spectrum shows a small trough at 583 nm that is absent in the analogous spectra of YCCP and HRP. Instead, this trough is similar to that seen for ferric myoglobin at about 585 nm, and is attributed (following spectral simulations) to a minor contribution (< or = 5%) in the spectrum of CCP (MKT) from a hexa-coordinate low-spin species in the form of a hydroxide-ligated heme. The MCD data indicate that the lyophilized sample of ferric YCCP (lambda CT = 637 nm) contains considerably increased amounts of hexa-coordinate low-spin species including both His/hydroxide and bis-His species. The crystal structure of a spectroscopically similar sample of CCP (MKT) (lambda CT = 637 nm) solved at 2.0 A resolution is consistent with His

  9. High-resolution dichroic imaging of magnetic flux distributions in superconductors with scanning x-ray microscopy

    SciTech Connect

    Ruoß, S. Stahl, C.; Weigand, M.; Schütz, G.; Albrecht, J.

    2015-01-12

    The penetration of magnetic flux into high-temperature superconductors has been observed using a high-resolution technique based on x-ray magnetic circular dichroism. Superconductors coated with thin soft-magnetic layers are observed in a scanning x-ray microscope under the influence of external magnetic fields. Resulting electric currents in the superconductor create an inhomogeneous magnetic field distribution above the superconductor and lead to a local reorientation of the ferromagnetic layer. Measuring the local magnetization of the ferromagnet by x-ray absorption microscopy with circular-polarized radiation allows the analysis of the magnetic flux distribution in the superconductor with a spatial resolution on the nanoscale.

  10. Spin exchange interaction in quasi-1D Cu-phthalocyanine crystalline thin film measured by Magnetic Circular Dichroism (MCD) spectroscopy

    NASA Astrophysics Data System (ADS)

    Pan, Zhenwen; Rawat, Naveen; Lamarche, Cody; Tokumoto, Takahisa; Wetherby, Anthony; Waterman, Rory; Headrick, Randy; McGill, Steve; Furis, Madalina

    2012-02-01

    Highly-oriented Cu-phthalocyanine (PC) pen-written crystalline thin films can be viewed as quasi-1D spin 1/2 magnetic chains. In order to reveal the nature of spin exchange between localized S=1/2 Cu spins, MCD spectroscopy was performed on films with millimeter-sized grains fabricated from a soluble CuPc derivative in magnetic fields up to 10 Tesla at temperatures ranging from 0.4 K to 77K. At T<2K and B<4T the MCD associated with transitions between Q-band π electron states exhibits a non-linear temperature-dependent Brillouin-like increase with magnetic field. For B>4T the MCD evolves linearly with magnetic field, as expected from diamagnetic carbon-based systems. Theoretical modelingootnotetextW. Wu et. al.,PRB 84,024427(2011) of electronic structure and exchange interactions in this system predicts an indirect exchange mechanism mediated by delocalized ligand states. Our MCD measurements identified the states responsible for this exchange.

  11. Magnetism of the endohedral metallofullerenes M@C82 (M=Gd,Dy) and the corresponding nanoscale peapods: Synchrotron soft x-ray magnetic circular dichroism and density-functional theory calculations

    NASA Astrophysics Data System (ADS)

    Kitaura, R.; Okimoto, H.; Shinohara, H.; Nakamura, T.; Osawa, H.

    2007-11-01

    Synchrotron soft x-ray magnetic circular dichroism (SXMCD) spectroscopy at the Gd and Dy M5 edges is reported on endohedral metallofullerenes ( M@C82 , M=Gd and Dy) and the corresponding nanopeapods [ (M@C82)@SWNT , SWNT represents single wall carbon nanotube] in a temperature range between 10 and 40K . The magnetic moment has also been determined by theoretical calculations, which are based on the Hartree-Fock approximation with relativistic corrections. Because of the element-specific measurement of SXMCD, magnetization processes of Gd and Dy ions of nanopeapods have been selectively observed. The temperature dependence of magnetic moments of the metallofullerenes and nanopeapods follows the Curie-Weiss law with a small Weiss temperature, indicating that the magnetic interaction between encapsulated rare-earth metal atoms is relatively weak. Although the observed differences in Curie constants and Weiss temperatures between Gd@C82 and (Gd@C82)@SWNT are small, those of Dy@C82 and (Dy@C82)@SWNT are significant. This observation is consistently explained by charge transfer-induced crystal-field effects.

  12. Resonant behaviour of MHD waves on magnetic flux tubes. I - Connection formulae at the resonant surfaces. II - Absorption of sound waves by sunspots

    NASA Technical Reports Server (NTRS)

    Sakurai, Takashi; Goossens, Marcel; Hollweg, Joseph V.

    1991-01-01

    The present method of addressing the resonance problems that emerge in such MHD phenomena as the resonant absorption of waves at the Alfven resonance point avoids solving the fourth-order differential equation of dissipative MHD by recourse to connection formulae across the dissipation layer. In the second part of this investigation, the absorption of solar 5-min oscillations by sunspots is interpreted as the resonant absorption of sounds by a magnetic cylinder. The absorption coefficient is interpreted (1) analytically, under certain simplifying assumptions, and numerically, under more general conditions. The observed absorption coefficient magnitude is explained over suitable parameter ranges.

  13. Dynamics of circular hydrogen bond array in calix[4]arene in a nonpolar solvent: A nuclear magnetic resonance study

    NASA Astrophysics Data System (ADS)

    Lang, Jan; Deckerová, Veronika; Czernek, Jiří; Lhoták, Pavel

    2005-01-01

    Hydroxyl groups on the lower rim of calix[4]arene form a circular array of four equivalent hydrogen bonds. The rate constants of reversal of the array in the temperature range of 221-304 K were determined by means of the NMR measurements of quaternary 13C nuclear spin transverse relaxation dependence on the effective radio frequency field. The flip-flop rate constants are in the range of 1.4×102-4.2×104s-1, the activation enthalpy is 36.8 kJ/mol, the activation entropy is -36 J mol-1 K-1. This process was found uncorrelated with conformational transition cone-inverted cone, which is about thousand times slower. Molecular tumbling of calix[4]arene measured using 13C spin relaxation was found isotropic with correlation times lying in the range of 0.1-3 ns and with the activation energy of 21 kJ/mol. In order to assess relaxation of 13C aromatic nuclei, their principal components of chemical shift tensor were calculated using the density functional theory approach.

  14. Origin-independent sum over states simulations of magnetic and electronic circular dichroism spectra via the localized orbital/local origin method.

    PubMed

    Štěpánek, Petr; Bouř, Petr

    2015-04-15

    Although electronic and magnetic circular dichroism (ECD, MCD) spectra reveal valuable details about molecular geometry and electronic structure, quantum-chemical simulations significantly facilitate their interpretation. However, the simulated results may depend on the choice of coordinate origin. Previously (Štěpánek and Bouř, J. Comput. Chem. 2013, 34, 1531), the sum-over-states (SOS) methodology was found useful for efficient MCD computations. Approximate wave functions were "resolved" using time-dependent density functional theory, and the origin-dependence was avoided by placing the origin to the center of mass of the investigated molecule. In this study, a more elegant way is proposed, based on the localized orbital/local origin (LORG) formalism, and a similar approach is also applied to generate ECD intensities. The LORG-like approach yields fully origin-independent ECD and MCD spectra. The results thus indicate that the computationally relatively cheap SOS simulations open a new way of modeling molecular properties, including those involving the origin-dependent magnetic dipole moment operator. PMID:25662937

  15. Magnetic field effect on natural convection and entropy generation in a half-moon shaped cavity with semi-circular bottom heater having different ferrofluid inside

    NASA Astrophysics Data System (ADS)

    Mojumder, Satyajit; Rabbi, Khan Md.; Saha, Sourav; Hasan, MN; Saha, Suvash C.

    2016-06-01

    In this study magneto-hydrodynamic convection in a half-moon shaped cavity filled with ferrofluid has been analyzed numerically. The cavity has two semi-circular bottom heaters and effect of the distance between these two heaters (λ = 0.1 , 0.4) has been thoroughly investigated. Numerical simulation has been carried out for a wide range of Rayleigh number (Ra =103 ∼107), Hartmann number (Ha = 0 ∼ 100) and inclination angle of magnetic field (γ = 0 ° ∼ 90 °) to understand the flow field, thermal field and entropy generation respectively. Cobalt-kerosene and Fe3 O4 -water ferrofluids are used for the present investigation and considered as a single phase fluid. Galerkin weighted residual method of finite element analysis has been used for numerical solution. The code validation and grid independency test have been carried out to justify the numerical accuracy. It has been observed that increment of magnetic field reduces the heat transfer rate, whereas increment of heater distance augments the heat transfer rate significantly. Results are discussed on the basis of Nusselt number (Nu), Bejan number (Be) and shown by contours and 3D plots. It has also been found that λ = 0.4 always shows better heat transfer rate and entropy optimization.

  16. Resonant vortex-core reversal in magnetic nano-spheres as robust mechanism of efficient energy absorption and emission

    NASA Astrophysics Data System (ADS)

    Kim, Sang-Koog; Yoo, Myoung-Woo; Lee, Jehyun; Lee, Jae-Hyeok; Kim, Min-Kwan

    2016-08-01

    We report on novel vortex-core reversal dynamics in nano-spheres of single-vortex spin configuration as revealed by micromagnetic simulations combined with analytical derivations. When the frequency of an AC magnetic field is tuned to the frequency of the vortex-core precession around the direction of a given static field, oscillatory vortex-core reversals occur, and additionally, the frequency is found to change with both the strength of the applied AC field and the particle size. Such resonant vortex-core reversals in nano-spheres may provide a new and efficient means of energy absorption by, and emission from, magnetic nanoparticles, which system can be effectively implemented in bio-applications such as magnetic hyperthermia.

  17. Resonant vortex-core reversal in magnetic nano-spheres as robust mechanism of efficient energy absorption and emission

    PubMed Central

    Kim, Sang-Koog; Yoo, Myoung-Woo; Lee, Jehyun; Lee, Jae-Hyeok; Kim, Min-Kwan

    2016-01-01

    We report on novel vortex-core reversal dynamics in nano-spheres of single-vortex spin configuration as revealed by micromagnetic simulations combined with analytical derivations. When the frequency of an AC magnetic field is tuned to the frequency of the vortex-core precession around the direction of a given static field, oscillatory vortex-core reversals occur, and additionally, the frequency is found to change with both the strength of the applied AC field and the particle size. Such resonant vortex-core reversals in nano-spheres may provide a new and efficient means of energy absorption by, and emission from, magnetic nanoparticles, which system can be effectively implemented in bio-applications such as magnetic hyperthermia. PMID:27531408

  18. Light absorption dichroism and magnetic configuration of weakly ferromagnetic CoCO 3

    NASA Astrophysics Data System (ADS)

    Litvinenko, Yu. G.; Verdyan, A. I.; Shapiro, V. V.

    1980-01-01

    Investigation of light interaction with magnetically ordered crystals [1] revealed a correlation between certain spectral characteristics of a crystal on the one hand and its magnetic properties on the other.

  19. Specific absorption rate dependence on temperature in magnetic field hyperthermia measured by dynamic hysteresis losses (ac magnetometry)

    NASA Astrophysics Data System (ADS)

    Garaio, Eneko; Sandre, Olivier; Collantes, Juan-Mari; Garcia, Jose Angel; Mornet, Stéphane; Plazaola, Fernando

    2015-01-01

    Magnetic nanoparticles (NPs) are intensively studied for their potential use for magnetic hyperthermia, a treatment that has passed a phase II clinical trial against severe brain cancer (glioblastoma) at the end of 2011. Their heating power, characterized by the ‘specific absorption rate (SAR)’, is often considered temperature independent in the literature, mainly because of the difficulties that arise from the measurement methodology. Using a dynamic magnetometer presented in a recent paper, we measure here the thermal dependence of SAR for superparamagnetic iron oxide (maghemite) NPs of four different size-ranges corresponding to mean diameters around 12 nm, 14 nm, 15 nm and 16 nm. The article reports a parametrical study extending from 10 to 60 {}^\\circ C in temperature, from 75 to 1031 kHz in frequency, and from 2 to 24 kA m-1 in magnetic field strength. It was observed that SAR values of smaller NPs decrease with temperature whereas for the larger sample (16 nm) SAR values increase with temperature. The measured variation of SAR with temperature is frequency dependent. This behaviour is fully explained within the scope of linear response theory based on Néel and Brown relaxation processes, using independent magnetic measurements of the specific magnetization and the magnetic anisotropy constant. A good quantitative agreement between experimental values and theoretical values is confirmed in a tri-dimensional space that uses as coordinates the field strength, the frequency and the temperature.

  20. Searching for magnetic fields in 11 Wolf-Rayet stars: Analysis of circular polarization measurements from ESPaDOnS

    SciTech Connect

    De la Chevrotière, A.; St-Louis, N.; Moffat, A. F. J.; Collaboration: MiMeS Collaboration

    2014-02-01

    With recent detections of magnetic fields in some of their progenitor O stars, combined with known strong fields in their possible descendant neutron stars, it is natural to search for magnetic fields in Wolf-Rayet (WR) stars, despite the problems associated with the presence of winds enhanced by an order of magnitude over those of O stars. We continue our search among a sample of 11 bright WR stars following our introductory study in a previous paper of WR6 = EZ CMa using the spectropolarimeter ESPaDOnS at Canada-France-Hawaii Telescope, most of them in all four Stokes parameters. This sample includes six WN stars and five WC stars encompassing a range of spectral subclasses. Six are medium/long-period binaries and three show corotating interaction regions. We report no definite detections of a magnetic field in the winds in which the lines form (which is about the same distance from the center of the star as it is from the surface of the progenitor O star) for any of the eleven stars. Possible reasons and their implications are discussed. Nonetheless, the data show evidence supporting marginal detections for WR134, WR137, and WR138. According to the Bayesian analysis, the most probable field intensities are B {sub wind} ∼ 200, 130, and 80 G, respectively, with a 95.4% probability that the magnetic fields present in the observable parts of their stellar wind, if stronger, does not exceed B{sub wind}{sup max}∼1900 G, ∼1500 G, and ∼1500 G, respectively. In the case of non-detections, we report an average field strength upper limit of B{sub wind}{sup max}∼500 G.

  1. An Energy-Stabilized Varied-Line-Space-Monochromator UndulatorBeam Line for PEEM Illumination and Magnetic Circular Dichroism

    SciTech Connect

    Warwick, Tony; McKinney, Wayne; Domning, Ed; Doran, Andrew; Padmore, Howard

    2006-06-01

    A new undulator beam line has been built and commissioned at the Advanced Light Source for illumination of the PEEM3 microscope. The beam line delivers high flux beams over an energy range from C1s through the transition metals to include the M edges of the magnetic rare earth elements. We present details of the optical design, and data on the performance of the zero-order tracking of the photon energy.

  2. Absorption lines from magnetically driven winds in X-ray binaries

    NASA Astrophysics Data System (ADS)

    Chakravorty, S.; Petrucci, P.-O.; Ferreira, J.; Henri, G.; Belmont, R.; Clavel, M.; Corbel, S.; Rodriguez, J.; Coriat, M.; Drappeau, S.; Malzac, J.

    2016-05-01

    Context. High resolution X-ray spectra of black hole X-ray binaries (BHBs) show blueshifted absorption lines suggesting the presence of outflowing winds. Furthermore, observations show that the disk winds are equatorial and they occur in the Softer (disk dominated) states of the outburst and are less prominent or absent in the Harder (power-law dominated) states. Aims: We want to test whether the self-similar magneto-hydrodynamic (MHD) accretion-ejection models can explain the observational results for accretion disk winds in BHBs. In our models, the density at the base of the outflow from the accretion disk is not a free parameter. This mass loading is determined by solving the full set of dynamical MHD equations without neglecting any physical term. Thus, the physical properties of the outflow depend on and are controlled by the global structure of the disk. Methods: We studied different MHD solutions characterized by different values of the disk aspect ratio (ɛ) and the ejection efficiency (p). We also generate two kinds of MHD solutions depending on the absence (cold solution) or presence (warm solution) of heating at the disk surface. Such heating could be either from dissipation of energy due to MHD turbulence in the disk or from illumination of the disk surface. Warm solutions can have large (>0.1) values of p, which would imply larger wind mass loading at the base of the outflow. We use each of these MHD solutions to predict the physical parameters (distance, density, velocity, magnetic field, etc.) of an outflow. Motivated by observational results, we have put limits on the ionization parameter (ξ), column density, and timescales. Further constraints were derived for the allowed values of ξ from thermodynamic instability considerations, particularly for the Hard SED. These physical constraints were imposed on each of these outflows to select regions within it, which are consistent with the observed winds. Results: The cold MHD solutions are found to be

  3. On self-consistent waves and their stability in warm plasmas. II - Instability of circularly polarized waves both in the presence and the absence of an ambient magnetic field

    NASA Technical Reports Server (NTRS)

    Lee, M. A.; Lerche, I.

    1980-01-01

    The stability of a self-consistent, large-amplitude, circularly polarized wave in a warm plasma is investigated. For perturbations to the system propagating normal to the plane of circular polarization, a dispersion relation is derived employing an expansion in the nonlinear wave amplitude and the momentum of the plasma particles in the plane of polarization. Instability results both in the absence and presence of a large-scale magnetic field with a growth rate of the order of the nonlinear wave amplitude.

  4. Facile Synthesis of Porous Nickel/Carbon Composite Microspheres with Enhanced Electromagnetic Wave Absorption by Magnetic and Dielectric Losses.

    PubMed

    Qiu, Song; Lyu, Hailong; Liu, Jiurong; Liu, Yuzhen; Wu, Nannan; Liu, Wei

    2016-08-10

    Porous nickel/carbon (Ni/C) composite microspheres with diameters of ca. 1.2-1.5 μm were fabricated by a solvothermal method combined with carbon reduction. The pore size of the synthesized Ni/C composite microspheres ranged from several nanometers to 50 nm. The porous Ni/C composite microspheres exhibited a saturation magnetization (MS) of 53.5 emu g(-1) and a coercivity (HC) of 51.4 Oe. When tested as an electromagnetic (EM) wave absorption material, the epoxy resin composites containing 60% and 75% porous Ni/C microspheres provided high-performance EM wave absorption at thicknesses of 3.0-11.0 and 1.6-7.0 mm in the corresponding frequency ranges of 2.0-12 and 2.0-18 GHz, respectively. The superior EM wave absorption performances of porous Ni/C composite microspheres were derived from the synergy effects generated by the magnetic loss of nickel, the dielectric loss of carbon, and the porous structure. PMID:27441382

  5. Morphology evolution, magnetic and microwave absorption properties of nano/submicrometre iron particles obtained at different reduced temperatures

    NASA Astrophysics Data System (ADS)

    Fan, Xi'an; Guan, Jianguo; Wang, Wei; Tong, Guoxiu

    2009-04-01

    Nano/submicrometre iron particles were prepared by a hydrogen reduction method in a fluidized bed furnace using α-FeOOH nanorods as precursors. The effect of the reducing temperature (T) on the microstructure, static magnetic properties, microwave electromagnetic parameters and microwave absorption properties of the resultant iron particles was investigated. When T increases from 450 to 650 °C, the as-obtained iron particles show an obvious morphology evolution from anisotropic nanorods to isotropic submicrometre polyhedra. As a result, the saturation magnetization, the complex permittivity and the real permeability all increase, while the coercivity and the imaginary permeability decrease due to the reducing surface effect and shape anisotropy. Nanocomposites containing 30 wt% iron nanorods obtained at 450 °C show a minimal reflection loss (RL) as low as -36.8 dB at 14.1 GHz and an absorption band with RL under -10 dB from 11.6 to 17.0 GHz when the thickness is 1.5 mm, suggesting that they are promising as a strong absorption, thin and lightweight microwave absorber.

  6. Facile Synthesis of Porous Nickel/Carbon Composite Microspheres with Enhanced Electromagnetic Wave Absorption by Magnetic and Dielectric Losses.

    PubMed

    Qiu, Song; Lyu, Hailong; Liu, Jiurong; Liu, Yuzhen; Wu, Nannan; Liu, Wei

    2016-08-10

    Porous nickel/carbon (Ni/C) composite microspheres with diameters of ca. 1.2-1.5 μm were fabricated by a solvothermal method combined with carbon reduction. The pore size of the synthesized Ni/C composite microspheres ranged from several nanometers to 50 nm. The porous Ni/C composite microspheres exhibited a saturation magnetization (MS) of 53.5 emu g(-1) and a coercivity (HC) of 51.4 Oe. When tested as an electromagnetic (EM) wave absorption material, the epoxy resin composites containing 60% and 75% porous Ni/C microspheres provided high-performance EM wave absorption at thicknesses of 3.0-11.0 and 1.6-7.0 mm in the corresponding frequency ranges of 2.0-12 and 2.0-18 GHz, respectively. The superior EM wave absorption performances of porous Ni/C composite microspheres were derived from the synergy effects generated by the magnetic loss of nickel, the dielectric loss of carbon, and the porous structure.

  7. The studies of high-frequency magnetic properties and absorption characteristics for amorphous-filler composites

    NASA Astrophysics Data System (ADS)

    Li, Z. W.; Yang, Z. H.

    2015-10-01

    Pure amorphous flake fillers and amorphous flakes coated by ferrite nanoparticles with core-shell-like structure were fabricated using mechanical ball-milling. The later with core-shell-like structure can greatly decrease permittivity and improve the absorption properties, as compared to the former. The absorption of all amorphous-filler composites has its origin in a quarter-wavelength resonator. Based on the resonator model, absorption frequency fA and the corresponding return loss RL are calculated, which are well consistent with observed values. It is also found that the resonance frequency is proportional to effective resistivity, based on William-Shockley-Kittel's eddy model.

  8. Thermal conductivity prediction of magnetic composite sheet for near-field electromagnetic absorption

    SciTech Connect

    Lee, Joonsik; Nam, Baekil; Ko, Frank K.; Kim, Ki Hyeon

    2015-05-07

    The magnetic composite sheets were designed by using core-shell structured magnetic fillers instead of uncoated magnetic fillers to resolve concurrently the electromagnetic interference and thermal radiation problems. To predict the thermal conductivity of composite sheet, we calculated the thermal conductivity of the uncoated magnetic fillers and core-shell structured fillers. And then, the thermal conductivity of the magnetic composites sheet filled with core-shell structured magnetic fillers was calculated and compared with that of the uncoated magnetic fillers filled in composite sheet. The magnetic core and shell material are employed the typical Fe-Al-Si flake (60 μm × 60 μm × 1 μm) and 250 nm-thick AlN with high thermal conductivity, respectively. The longitudinal thermal conductivity of the core-shell structured magnetic composite sheet (2.45 W/m·K) enhanced about 33.4% in comparison with that of uncoated magnetic fillers (1.83 W/m·K) for the 50 vol. % magnetic filler in polymer matrix.

  9. Coordination modes of tyrosinate-ligated catalase-type heme enzymes: magnetic circular dichroism studies of Plexaura homomalla allene oxide synthase, Mycobacterium avium ssp. paratuberculosis protein-2744c, and bovine liver catalase in their ferric and ferrous states.

    PubMed

    Bandara, D M Indika; Sono, Masanori; Bruce, Grant S; Brash, Alan R; Dawson, John H

    2011-12-01

    Bovine liver catalase (BLC), catalase-related allene oxide synthase (cAOS) from Plexaura homomalla, and a recently isolated protein from the cattle pathogen Mycobacterium avium ssp. paratuberculosis (MAP-2744c (MAP)) are all tyrosinate-ligated heme enzymes whose crystal structures have been reported. cAOS and MAP have low (<20%) sequence similarity to, and significantly different catalytic functions from, BLC. cAOS transforms 8R-hydroperoxy-eicosatetraenoic acid to an allene epoxide, whereas the MAP protein is a putative organic peroxide-dependent peroxidase. To elucidate factors influencing the functions of these and related heme proteins, we have investigated the heme iron coordination properties of these tyrosinate-ligated heme enzymes in their ferric and ferrous states using magnetic circular dichroism and UV-visible absorption spectroscopy. The MAP protein shows remarkable spectral similarities to cAOS and BLC in its native Fe(III) state, but clear differences from ferric proximal heme ligand His93Tyr Mb (myoglobin) mutant, which may be attributed to the presence of an Arg(+)-N(ω)-H···¯O-Tyr (proximal heme axial ligand) hydrogen bond in the first three heme proteins. Furthermore, the spectra of Fe(III)-CN¯, Fe(III)-NO, Fe(II)-NO (except for five-coordinate MAP), Fe(II)-CO, and Fe(II)-O(2) states of cAOS and MAP, but not H93Y Mb, are also similar to the corresponding six-coordinate complexes of BLC, suggesting that a tyrosinate (Tyr-O¯) is the heme axial ligand trans to the bound ligands in these complexes. The Arg(+)-N(ω)-H to ¯O-Tyr hydrogen bond would be expected to modulate the donor properties of the proximal tyrosinate oxyanion and, combined with the subtle differences in the catalytic site structures, affect the activities of cAOS, MAP and BLC. PMID:22104301

  10. Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field

    SciTech Connect

    Kushwaha, Manvir S.

    2014-12-15

    Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes) – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines’ random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level

  11. Multimodal Superparamagnetic Nanoparticles with Unusually Enhanced Specific Absorption Rate for Synergetic Cancer Therapeutics and Magnetic Resonance Imaging.

    PubMed

    Thorat, Nanasaheb D; Bohara, Raghvendra A; Malgras, Victor; Tofail, Syed A M; Ahamad, Tansir; Alshehri, Saad M; Wu, Kevin C-W; Yamauchi, Yusuke

    2016-06-15

    Superparamagnetic nanoparticles (SPMNPs) used for magnetic resonance imaging (MRI) and magnetic fluid hyperthermia (MFH) cancer therapy frequently face trade off between a high magnetization saturation and their good colloidal stability, high specific absorption rate (SAR), and most importantly biological compatibility. This necessitates the development of new nanomaterials, as MFH and MRI are considered to be one of the most promising combined noninvasive treatments. In the present study, we investigated polyethylene glycol (PEG) functionalized La1-xSrxMnO3 (LSMO) SPMNPs for efficient cancer hyperthermia therapy and MRI application. The superparamagnetic nanomaterial revealed excellent colloidal stability and biocompatibility. A high SAR of 390 W/g was observed due to higher colloidal stability leading to an increased Brownian and Neel's spin relaxation. Cell viability of PEG capped nanoparticles is up to 80% on different cell lines tested rigorously using different methods. PEG coating provided excellent hemocompatibility to human red blood cells as PEG functionalized SPMNPs reduced hemolysis efficiently compared to its uncoated counterpart. Magnetic fluid hyperthermia of SPMNPs resulted in cancer cell death up to 80%. Additionally, improved MRI characteristics were also observed for the PEG capped La1-xSrxMnO3 formulation in aqueous medium compared to the bare LSMO. Taken together, PEG capped SPMNPs can be useful for diagnosis, efficient magnetic fluid hyperthermia, and multimodal cancer treatment as the amphiphilicity of PEG can easily be utilized to encapsulate hydrophobic drugs. PMID:27197993

  12. Multimodal Superparamagnetic Nanoparticles with Unusually Enhanced Specific Absorption Rate for Synergetic Cancer Therapeutics and Magnetic Resonance Imaging.

    PubMed

    Thorat, Nanasaheb D; Bohara, Raghvendra A; Malgras, Victor; Tofail, Syed A M; Ahamad, Tansir; Alshehri, Saad M; Wu, Kevin C-W; Yamauchi, Yusuke

    2016-06-15

    Superparamagnetic nanoparticles (SPMNPs) used for magnetic resonance imaging (MRI) and magnetic fluid hyperthermia (MFH) cancer therapy frequently face trade off between a high magnetization saturation and their good colloidal stability, high specific absorption rate (SAR), and most importantly biological compatibility. This necessitates the development of new nanomaterials, as MFH and MRI are considered to be one of the most promising combined noninvasive treatments. In the present study, we investigated polyethylene glycol (PEG) functionalized La1-xSrxMnO3 (LSMO) SPMNPs for efficient cancer hyperthermia therapy and MRI application. The superparamagnetic nanomaterial revealed excellent colloidal stability and biocompatibility. A high SAR of 390 W/g was observed due to higher colloidal stability leading to an increased Brownian and Neel's spin relaxation. Cell viability of PEG capped nanoparticles is up to 80% on different cell lines tested rigorously using different methods. PEG coating provided excellent hemocompatibility to human red blood cells as PEG functionalized SPMNPs reduced hemolysis efficiently compared to its uncoated counterpart. Magnetic fluid hyperthermia of SPMNPs resulted in cancer cell death up to 80%. Additionally, improved MRI characteristics were also observed for the PEG capped La1-xSrxMnO3 formulation in aqueous medium compared to the bare LSMO. Taken together, PEG capped SPMNPs can be useful for diagnosis, efficient magnetic fluid hyperthermia, and multimodal cancer treatment as the amphiphilicity of PEG can easily be utilized to encapsulate hydrophobic drugs.

  13. Comparison of the magnetic properties of GeMn thin films through Mn L-edge x-ray absorption

    SciTech Connect

    Ahlers, S.; Stone, P.R.; Sircar, N.; Arenholz, E.; Dubon, O. D.; Bougeard, D.

    2009-08-04

    X-ray absorption spectroscopy of epitaxial GeMn thin films reveals an experimentally indistinguishable electronic configuration of Mn atoms incorporated in Ge{sub 1?x}Mn{sub x} nanoclusters and in precipitates of the intermetallic compound Mn{sub 5}Ge{sub 3}, respectively. However, the average magnetic response of thin films containing Ge{sub 1?x}Mn{sub x} nanoclusters is lower than the response of films containing Mn{sub 5}Ge{sub 3} precipitates. This reduced magnetic response of Ge{sub 1?x}Mn{sub x} nanoclusters is explained in terms of a fraction of Mn atoms being magnetically inactive due to antiferromagnetic coupling or the presence of structural disorder. A determination of the role of magnetically inactive Mn atoms in the self-assembly of the thermodynamically metastable Ge{sub 1?x}Mn{sub x} nanoclusters seems to be an essential ingredient for an enhanced control of this promising high Curie temperature magnetic semiconductor.

  14. Magnetic circular dichroism study of the selenium-substituted form (Fe3Se4) of bovine heart aconitase.

    PubMed Central

    Breton, J L; Farrar, J A; Kennedy, M C; Beinert, H; Thomson, A J

    1995-01-01

    The selenium-substituted inactive form of mitochondrial aconitase contains one [3Fe-4Se]1+/0 cluster [Surerus, Kennedy, Beinert and Münck (1989) Proc. Natl. Acad. Sci. U.S.A. 87, 9846-9850]. This cluster was studied in both oxidized and reduced states by magnetic CD (MCD) and EPR spectroscopy. In the MCD spectra, intensity and transition wavelength shifts are observed when compared with the spectra of the native [3Fe-4S]1+/0 cluster. These changes are used to differentiate between the charge-transfer transitions originating from inorganic and cysteinyl sulphur. Using also the data from the EPR spectra, the spin ground state is assigned as S = 1/2 for the oxidized [3Fe-4Se]1+ cluster and S = 2 for the reduced [3Fe-4Se]0 cluster. PMID:7575454

  15. Circular causality.

    PubMed

    Thomas, R

    2006-07-01

    The problem of disentangling complex dynamic systems is addressed, especially with a view to identifying those variables that take part in the essential qualitative behaviour of systems. The author presents a series of reflections about the methods of formalisation together with the principles that govern the global operation of systems. In particular, a section on circuits, nuclei, and circular causality and a rather detailed description of the analytic use of the generalised asynchronous logical description, together with a brief description of its synthetic use (OreverseO logic). Some basic rules are recalled, such as the fact that a positive circuit is a necessary condition of multistationarity. Also, the interest of considering as a model, rather than a well-defined set of differential equations, a variety of systems that differ from each other only by the values of constant terms is emphasised. All these systems have a common Jacobian matrix and for all of them phase space has exactly the same structure. It means that all can be partitioned in the same way as regards the signs of the eigenvalues and thus as regards the precise nature of any steady states that might be present. Which steady states are actually present, depends on the values of terms of order zero in the ordinary differential equations (ODEs), and it is easy to find for which values of these terms a given point in phase space is steady. Models can be synthesised first at the level of the circuits involved in the Jacobian matrix (that determines which types and numbers of steady states are consistent with the model), then only at the level of terms of order zero in the ODE's (that determines which of the steady states actually exist), hence the title 'Circular casuality'.

  16. Impact of ZnO substitution on magnetic response and microwave absorption capability of strontium-natural nanoferrites

    NASA Astrophysics Data System (ADS)

    Widanarto, W.; Rahayu, F. M.; Ghoshal, S. K.; Effendi, M.; Cahyanto, W. T.

    Ferrite being a compound derived from iron oxides including magnetite and hematite possesses similar properties as ceramics which are hard and brittle. Certainly, the mounting demand for electronics has been a major factor driving the exponential growth of ferrite based materials. ZnO doped strontium-natural nanoferrites of composition (80 - x)Fe2O3:xZnO:20SrCO3, where x = 0, 10, 20 mol% are synthesized and sintered via the solid state reaction scheme. Samples are characterized by SEM, XRD, VSM, and VNA measurements to determine the impact of ZnO contents' variation on the surface morphology, structure, magnetic and microwave absorption properties. The Nicolson-Ross-Weir method is applied to evaluate samples' reflection loss. The average grain size of the strontium ferrite is found to reduce with the increase in ZnO concentration. Materials sintered at 1100 °C without ZnO incorporation are composed of hexagonal SrFe12O19. Meanwhile, the addition of ZnO produces cubic ZnFe2O4 and SrFeO2 phases. Insertion of ZnO results in reduction of magnetic parameters and reflection loss. Furthermore, the anisotropy magnetic field of strontium natural ferrites displays a rapid drop from 350 kA/m to 79.6 kA/m with the increase in ZnO. Strontium ferrite containing 20 mol% of ZnO exhibits superior microwave absorption with reflection loss within -45 dB to -55.94 dB in the frequency range of 7-13 GHz. This facilely synthesized a new class of materials which is believed to be economically promising for microwave absorption applications in the GHz range.

  17. Magnetic Spinner

    NASA Astrophysics Data System (ADS)

    Ouseph, P. J.

    2006-12-01

    A science toy sometimes called the "magnetic spinner" is an interesting class demonstration to illustrate the principles of magnetic levitation. It can also be used to demonstrate Faraday's law and a horizontally suspended physical pendulum. The levitated part contains two circular magnets encased in a plastic housing. Each magnet stays above two triangular magnets fixed to the base. The magnetic repulsive force experienced by the circular magnets is independent of their orientation; therefore, the holder of these magnets can be rotated without affecting its stability. The holder with the circular magnets can be oscillated up and down as a horizontally suspended physical pendulum.

  18. Effect of the concentration of magnetic grains on the linear-optical-absorption coefficient of ferrofluid-doped lyotropic mesophases: deviation from the Beer-Lambert law.

    PubMed

    Cuppo, F L S; Gómez, S L; Figueiredo Neto, A M

    2004-04-01

    In this paper is reported a systematic experimental study of the linear-optical-absorption coefficient of ferrofluid-doped isotropic lyotropic mixtures as a function of the magnetic-grains concentration. The linear optical absorption of ferrolyomesophases increases in a nonlinear manner with the concentration of magnetic grains, deviating from the usual Beer-Lambert law. This behavior is associated to the presence of correlated micelles in the mixture which favors the formation of small-scale aggregates of magnetic grains (dimers), which have a higher absorption coefficient with respect to that of isolated grains. We propose that the indirect heating of the micelles via the ferrofluid grains (hyperthermia) could account for this nonlinear increase of the linear-optical-absorption coefficient as a function of the grains concentration.

  19. Interaction of bovine serum albumin (BSA) with novel gemini surfactants studied by synchrotron radiation scattering (SR-SAXS), circular dichroism (CD), and nuclear magnetic resonance (NMR).

    PubMed

    Gospodarczyk, W; Szutkowski, K; Kozak, M

    2014-07-24

    The interaction of three dicationic (gemini) surfactants-3,3'-[1,6-(2,5-dioxahexane)]bis(1-dodecylimidazolium) chloride (oxyC2), 3,3'-[1,16-(2,15-dioxahexadecane)]bis(1-dodecylimidazolium) chloride (oxyC12), and 1,4-bis(butane)imidazole-1-yl-3-dodecylimidazolium chloride (C4)--with bovine serum albumin (BSA) has been studied by the use of small-angle X-ray scattering (SAXS), circular dichroism (CD), and (1)H nuclear magnetic resonance diffusometry. The results of CD studies show that the conformation of BSA was changed dramatically in the presence of all studied surfactants. The greater decrease (from 56 to 24%) in the α-helical structure of BSA was observed for oxyC2 surfactant. The radii of gyration estimated from SAXS data varied between 3 and 26 nm for the BSA/oxyC2 and BSA/oxyC12 systems. The hydrodynamic radius of the BSA/surfactant system estimated from NMR diffusometry varies between 5 and 11 nm for BSA/oxyC2 and 5 and 8 nm for BSA/oxyC12.

  20. Mulliken Population Analysis of X-ray Magnetic Circular Dichroism in Uranium Monochalcogenides: Examination of Sum Rules by Fully Relativistic Full-Potential LCAO Method

    NASA Astrophysics Data System (ADS)

    Suzuki, Shugo; Ariizumi, Toshihiro; Li, Ming-Fang

    2009-07-01

    We study the X-ray magnetic circular dichroism (XMCD) spectra at the U M4,5 and N4,5 edges of uranium monochalcogenides, UX where X=S, Se, and Te, examining the applicability of the XMCD sum rules to UX by the fully relativistic full-potential linear-combination-of-atomic-orbitals (LCAO) method based on the density functional theory. To extract the transitions relevant to the sum-rule analysis, we employ the Mulliken population analysis (MPA). Using the MPA, the orbital sum rule is found to be valid to 10-20% for the M4,5 edges and valid to 5-15% for the N4,5 edges. On the other hand, the spin sum rule is found to be valid to 10-20% for the M4,5 edges whereas valid to 30-35% for the N4,5 edges. Furthermore, it is found that the calculated XMCD spectra are consistent with a recent experimental observation that the intensity of the N4,5 XMCD signal is comparable to that of the M4,5 XMCD signal although contradicting a previous theoretical prediction that the XMCD intensity at the N4,5 edges is one order of magnitude smaller than that at the M4,5 edges.

  1. High resolution soft x-ray bending magnet beamline 9.3.2 with circularly polarized radiation capability at the Advanced Light Source

    SciTech Connect

    Hussain, Z.; Heimann, P.A.; McKinney, W.; Padmore, H.A.; Huff, W.R.A.; Kellar, S.A.; Moler, E.J. |; Fadley, C.S. |; Shirley, D.A.

    1995-08-01

    Bending magnet beamline 9.3.2 at the Advanced Light Source (ALS) was designed for high resolution spectroscopy in the soft x-ray energy region, covering a range from 30 eV to 1500 eV with three gratings. The monochromator itself is a standard fixed included angle 55 m spherical grating monochromator and was originally used at the Stanford Synchrotron Radiation Laboratory (SSRL) as a prototype for later insertion device based monochromators for the ALS. For operations at the ALS, the toroidal pre-mirror used at SSRL to vertically focus onto the entrance slit and horizontally focus onto the exit slit was replaced by two separate crossed mirrors (Kirkpatrick-Baez configuration). Circularly polarized radiation is obtained by inserting a water-cooled movable aperture in front of the vertically focusing mirror to allow selecting the beam either above or below the horizontal plane. To maintain a stable beam intensity through the entrance slit, the photocurrent signals from the upper and lower jaws of the entrance slit are utilized to set a feedback loop with the vertically deflecting mirror Piezoelectric drive. The beamline end station has a rotatable platform (through 60{degree}) that accommodates two experimental chambers, enabling the synchrotron radiation to be directed to either one without breaking vacuum.

  2. High-Magnetization FeCo Nanochains with Ultrathin Interfacial Gaps for Broadband Electromagnetic Wave Absorption at Gigahertz.

    PubMed

    Zhang, Xuefeng; Li, Yixing; Liu, Rongge; Rao, Yi; Rong, Huawei; Qin, Gaowu

    2016-02-10

    Superparamagnetic FeCo nanochains consisting of assembled ∼25 nm nanoparticles and ∼1 nm gaps are synthesized by facial wet-chemical route and exhibit significant electromagnetic absorption at gigahertz. Both the dielectric and magnetic loss factors present dual-resonance behaviors at 2-18 GHz frequencies, originated from the asymmetric architecture of the cubic FeCo particles that assembled in a one-dimensional chain structure. Theoretical analyses uncover that the origins of the enhancement of electromagnetic losses are ascribed to the high magnetization (228 emu/g) and the ultrathin gaps (∼1 nm), which enhances the Snoek limit and induces anisotropic dielectric polarizations, consequently constructing a proper electromagnetic match.

  3. High-Magnetization FeCo Nanochains with Ultrathin Interfacial Gaps for Broadband Electromagnetic Wave Absorption at Gigahertz.

    PubMed

    Zhang, Xuefeng; Li, Yixing; Liu, Rongge; Rao, Yi; Rong, Huawei; Qin, Gaowu

    2016-02-10

    Superparamagnetic FeCo nanochains consisting of assembled ∼25 nm nanoparticles and ∼1 nm gaps are synthesized by facial wet-chemical route and exhibit significant electromagnetic absorption at gigahertz. Both the dielectric and magnetic loss factors present dual-resonance behaviors at 2-18 GHz frequencies, originated from the asymmetric architecture of the cubic FeCo particles that assembled in a one-dimensional chain structure. Theoretical analyses uncover that the origins of the enhancement of electromagnetic losses are ascribed to the high magnetization (228 emu/g) and the ultrathin gaps (∼1 nm), which enhances the Snoek limit and induces anisotropic dielectric polarizations, consequently constructing a proper electromagnetic match. PMID:26775668

  4. Excellent improvement in the static and dynamic magnetic properties of carbon coated iron nanoparticles for microwave absorption

    NASA Astrophysics Data System (ADS)

    Khani, Omid; Shoushtari, Morteza Zargar; Farbod, Mansoor

    2015-11-01

    Carbon coated iron nanoparticles were synthesized, using a simple arc-discharge method. The morphology and the internal structure of the core/shell nanoparticles were studied, using field emission scanning electron microscopy and transmission electron microscopy. X-ray diffraction analysis showed that both magnetic α-Fe and nonmagnetic γ-Fe phases existed in the as-prepared particles. In order to improve the static and dynamic magnetic properties of the core/shell nanoparticles, the produced nanocapsules were annealed in argon atmosphere at two different temperatures. Hysteresis loops revealed that the value of the saturation magnetization (MS) increased more than 4.1 times of its original value by annealing and this led to 70% increase in the imaginary part of the permeability. Phase analysis showed that heat treatment eliminated the nonmagnetic γ-Fe phase completely. The reflection loss plots were studied for composite layers containing 20 vol% of the annealed and not annealed nanocapsules. One of the absorber layers which contained annealed nanocapsules showed at least -10 dB loss in the whole G, C, X and Ku frequency bands and the optimal absorption exceeded -37 dB at 5.8 GHz for the as-prepared sample with a thickness of 3.2 mm. The results revealed that the magnetic properties of the arc-made Fe/C core/shell nanoparticle can be improved significantly by annealing in argon.

  5. Microstrip Antenna Generates Circularly Polarized Beam

    NASA Technical Reports Server (NTRS)

    Huang, J.

    1986-01-01

    Circular microstrip antenna excited with higher order transverse magnetic (TM) modes generates circularly polarized, conical radiation patterns. Found both theoretically and experimentally that peak direction of radiation pattern is varied within wide angular range by combination of mode selection and loading substrate with materials of different dielectric constants.

  6. Incident Angle- and Polarization-Insensitive Metamaterial Absorber using Circular Sectors

    PubMed Central

    Lee, Dongju; Hwang, Jung Gyu; Lim, Daecheon; Hara, Tadayoshi; Lim, Sungjoon

    2016-01-01

    In this paper, an incident angle- and polarization-insensitive metamaterial absorber is proposed for X-band applications. A unit cell of the proposed absorber has a square patch at the centre and four circular sectors are rotated around the square patch. The vertically and horizontally symmetric structure of the unit cell enables polarization-insensitivity. The circular sector of the unit cell enables an angle-insensitivity. The performances of the proposed absorber are demonstrated with a full-wave simulation and measurements. The angular sensitivity is studied at different inner angles of the circular sector. When the inner angle of the circular sector is 90°, the simulated absorptivity is higher than 90%, and the frequency variation is less than 0.96% for incident angles up to 70°. The measured absorptivity at 10.44 GHz is close to 100% for all the polarization angles under normal incidence. When the incident angles are varied from 0°– 60°, the measured absorptivity is maintained above 90% for both the transverse electric (TE) and the transverse magnetic (TM) modes. PMID:27257089

  7. Nuclear spin circular dichroism

    SciTech Connect

    Vaara, Juha; Rizzo, Antonio; Kauczor, Joanna; Norman, Patrick; Coriani, Sonia

    2014-04-07

    Recent years have witnessed a growing interest in magneto-optic spectroscopy techniques that use nuclear magnetization as the source of the magnetic field. Here we present a formulation of magnetic circular dichroism (CD) due to magnetically polarized nuclei, nuclear spin-induced CD (NSCD), in molecules. The NSCD ellipticity and nuclear spin-induced optical rotation (NSOR) angle correspond to the real and imaginary parts, respectively, of (complex) quadratic response functions involving the dynamic second-order interaction of the electron system with the linearly polarized light beam, as well as the static magnetic hyperfine interaction. Using the complex polarization propagator framework, NSCD and NSOR signals are obtained at frequencies in the vicinity of optical excitations. Hartree-Fock and density-functional theory calculations on relatively small model systems, ethene, benzene, and 1,4-benzoquinone, demonstrate the feasibility of the method for obtaining relatively strong nuclear spin-induced ellipticity and optical rotation signals. Comparison of the proton and carbon-13 signals of ethanol reveals that these resonant phenomena facilitate chemical resolution between non-equivalent nuclei in magneto-optic spectra.

  8. Magnetic feature and near-infrared absorption of a [Pt(mnt)2]--based H-bond supramolecular crystal

    NASA Astrophysics Data System (ADS)

    Li, Cui-Ping; Nie, Li; Pei, Wen-Bo; Li, Li; Tian, Zheng-Fang; Liu, Jian-Lan; Gao, Xu-Sheng; Ren, Xiao-Ming

    2016-11-01

    A new salt [H2DABCO][Pt(mnt)2]2 (1) (mnt2-=maleonitriledithiolate and H2DABCO2+ is diprotonated 1,4-diazabicyclo[2.2.2]octane) has been synthesized; its crystal structure, magnetic and near-IR absorption properties have been investigated. Two different [Pt(mnt)2]- anions form the strong π-dimers, labeled as Pt(1)-dimer and Pt(2)-dimer, with quite shorter Pt…Pt and S…S distances and molecular plane-to-plane distance (<3.5 Å) within a dimer. The [Pt(mnt)2]22- π-dimers are connected through the cations in the strong H-bond manner to form three-dimensional H-bond supramolecular crystal. The salt shows weak paramagnetism in 1.99-300 K and this is due to the existence of strong antiferromagnetic coupling within a π-dimer. In addition, a small thermal hysteresis loop is observed at ca. 120 K, indicating that a phase transition probably occurs that is further confirmed by variable-temperature IR spectra. Another fascinating functionality of 1 is the intense near-IR absorption in the region of 750-2500 nm, and this near-IR absorption feature makes it to be a promising optical material.

  9. Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

    PubMed Central

    Stigliano, Robert; Baker, Ian

    2015-01-01

    Magnetic nanoparticles (MNPs), referred to as the Dartmouth MNPs, which exhibit high specific absorption rate at low applied field strength have been developed for hyperthermia therapy applications. The MNPs consist of small (2–5 nm) single crystals of gamma-Fe2O3 with saccharide chains implanted in their crystalline structure, forming 20–40 nm flower-like aggregates with a hydrodynamic diameter of 110–120 nm. The MNPs form stable (>12 months) colloidal solutions in water and exhibit no hysteresis under an applied quasistatic magnetic field, and produce a significant amount of heat at field strengths as low as 100 Oe at 99–164 kHz. The MNP heating mechanisms under an alternating magnetic field (AMF) are discussed and analyzed quantitatively based on (a) the calculated multi-scale MNP interactions obtained using a three dimensional numerical model called the method of auxiliary sources, (b) measured MNP frequency spectra, and (c) quantified MNP friction losses based on magneto-viscous theory. The frequency responses and hysteresis curves of the Dartmouth MNPs are measured and compared to the modeled data. The specific absorption rate of the particles is measured at various AMF strengths and frequencies, and compared to commercially available MNPs. The comparisons demonstrate the superior heating properties of the Dartmouth MNPs at low field strengths (<250 Oe). This may extend MNP hyperthermia therapy to deeper tumors that were previously non-viable targets, potentially enabling the treatment of some of the most difficult cancers, such as pancreatic and rectal cancers, without damaging normal tissue. PMID:25825545

  10. Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

    NASA Astrophysics Data System (ADS)

    Shubitidze, Fridon; Kekalo, Katsiaryna; Stigliano, Robert; Baker, Ian

    2015-03-01

    Magnetic nanoparticles (MNPs), referred to as the Dartmouth MNPs, which exhibit high specific absorption rate at low applied field strength have been developed for hyperthermia therapy applications. The MNPs consist of small (2-5 nm) single crystals of gamma-Fe2O3 with saccharide chains implanted in their crystalline structure, forming 20-40 nm flower-like aggregates with a hydrodynamic diameter of 110-120 nm. The MNPs form stable (>12 months) colloidal solutions in water and exhibit no hysteresis under an applied quasistatic magnetic field, and produce a significant amount of heat at field strengths as low as 100 Oe at 99-164 kHz. The MNP heating mechanisms under an alternating magnetic field (AMF) are discussed and analyzed quantitatively based on (a) the calculated multi-scale MNP interactions obtained using a three dimensional numerical model called the method of auxiliary sources, (b) measured MNP frequency spectra, and (c) quantified MNP friction losses based on magneto-viscous theory. The frequency responses and hysteresis curves of the Dartmouth MNPs are measured and compared to the modeled data. The specific absorption rate of the particles is measured at various AMF strengths and frequencies, and compared to commercially available MNPs. The comparisons demonstrate the superior heating properties of the Dartmouth MNPs at low field strengths (<250 Oe). This may extend MNP hyperthermia therapy to deeper tumors that were previously non-viable targets, potentially enabling the treatment of some of the most difficult cancers, such as pancreatic and rectal cancers, without damaging normal tissue.

  11. Tuning the magnetic property of vacancy-defected graphyne by transition metal absorption

    SciTech Connect

    Bhattacharya, Barnali; Singh, Ngangbam Bedamani; Sarkar, Utpal

    2015-06-24

    In this work, we demonstrate a novel and simple approach to tune the electronic properties as well as magnetic properties of transition metal absorbed in vacancy-defected graphyne (VGY). A double vacancy has been introduced in the graphyne unit and TM atoms (V-Cu) are systematically doped in the vacant site. We find that combination of these two give rise to some interesting spintronics properties such as half-metalicity, and spin-select half-semiconductivity. Furthermore, the magnetic moments of TM absorbed vacancy-defected graphyne are found to be higher compare to TM absorbed graphyne. Although Ni absorbed graphyne is nonmagnetic in nature, we find that the Ni absorbed VGY behaves as half metal with a net magnetic moment of 2 µ{sub B} and can be used as spin filter. Thus, the TM absorbed vacancy-defected graphyne are more suitable candidate for magneto-optics and spintronics.

  12. CIRCULAR RIBBON FLARES AND HOMOLOGOUS JETS

    SciTech Connect

    Wang Haimin; Liu Chang

    2012-12-01

    Solar flare emissions in the chromosphere often appear as elongated ribbons on both sides of the magnetic polarity inversion line (PIL), which has been regarded as evidence of a typical configuration of magnetic reconnection. However, flares having a circular ribbon have rarely been reported, although it is expected in the fan-spine magnetic topology involving reconnection at a three-dimensional (3D) coronal null point. We present five circular ribbon flares with associated surges, using high-resolution and high-cadence H{alpha} blue wing observations obtained from the recently digitized films of Big Bear Solar Observatory. In all the events, a central parasitic magnetic field is encompassed by the opposite polarity, forming a circular PIL traced by filament material. Consequently, a flare kernel at the center is surrounded by a circular flare ribbon. The four homologous jet-related flares on 1991 March 17 and 18 are of particular interest, as (1) the circular ribbons brighten sequentially, with cospatial surges, rather than simultaneously, (2) the central flare kernels show an intriguing 'round-trip' motion and become elongated, and (3) remote brightenings occur at a region with the same magnetic polarity as the central parasitic field and are co-temporal with a separate phase of flare emissions. In another flare on 1991 February 25, the circular flare emission and surge activity occur successively, and the event could be associated with magnetic flux cancellation across the circular PIL. We discuss the implications of these observations combining circular flare ribbons, homologous jets, and remote brightenings for understanding the dynamics of 3D magnetic restructuring.

  13. Synthesis, dual-nonlinear magnetic resonance and microwave absorption properties of nanosheet hierarchical cobalt particles.

    PubMed

    Wen, S L; Liu, Y; Zhao, X C; Cheng, J W; Li, H

    2014-09-14

    In this paper, we report the synthesis of three kinds of novel nanosheet hierarchical cobalt particles by adjusting the [C4H4O6](2-)/Co(2+) ratio through a liquid reduction method. We investigated the electromagnetic properties of the cobalt particles in detail over the microwave frequency range of 1-18 GHz. The results show that the real part of the permittivity decreases and the imaginary part of the permeability increases with an increase in the [C4H4O6](2-)/Co(2+) ratio. The permeability displays two resonance peaks over the frequency range. The cobalt particles with [C4H4O6](2-)/Co(2+) = 6 have a maximum reflection loss of -48.03 dB at 13.61 GHz, and the effective absorption bandwidth (RL ≤ -10 dB) is 6.76 GHz corresponding to a thickness of 1.7 mm. Considering the impedance matching and attenuation based on the electromagnetic parameters, we designed a way to obtain cobalt particles with excellent microwave absorption properties by decreasing the real part of permittivity and increasing the imaginary part of permeability.

  14. Enhancement of two photon absorption with Ni doping in the dilute magnetic semiconductor ZnO crystalline nanorods

    SciTech Connect

    Rana, Amit Kumar; Kumar, Yogendra; Arjunan, M.S.; Sen, Somaditya; Shirage, Parasharam M. E-mail: paras.shirage@gmail.com; J, Aneesh; Adarsh, K. V.

    2015-12-07

    In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient (β) increases by as much as 14 times, i.e., 7.6 ± 0.4 to 112 ± 6 cm/GW, when the Ni doping is increased from 0% to 10%. The substantial enhancement in β is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UV-Vis and photoluminescence spectroscopies, continuously redshift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.

  15. Enhancement of two photon absorption with Ni doping in the dilute magnetic semiconductor ZnO crystalline nanorods

    NASA Astrophysics Data System (ADS)

    Rana, Amit Kumar; J, Aneesh; Kumar, Yogendra; M. S, Arjunan; Adarsh, K. V.; Sen, Somaditya; Shirage, Parasharam M.

    2015-12-01

    In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient (β) increases by as much as 14 times, i.e., 7.6 ± 0.4 to 112 ± 6 cm/GW, when the Ni doping is increased from 0% to 10%. The substantial enhancement in β is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UV-Vis and photoluminescence spectroscopies, continuously redshift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.

  16. Nuclear Magnetic Resonance and X-Ray Absorption Spectroscopic Studies of Lithium Insertion in Silver Vanadium Oxide Cathodes

    SciTech Connect

    Leifer,N.; Colon, A.; Martocci, k.; Greenbaum, S.; Alamgir, F.; Reddy, T.; Gleason, N.; Leising, R.; Takeuchi, E.

    2007-01-01

    Structural studies have been carried out on Ag{sub 2}V{sub 4}O{sub 11} (silver vanadium oxide, SVO) and Li{sub x}Ag{sub 2}V{sub 4}O{sub 11}, lithiated SVO with x=0.72, 2.13, and 5.59 using nuclear magnetic resonance (NMR) and X-ray absorption spectroscopy (XAS). Lithium-7 NMR indicates the formation of a solid electrolyte interphase layer on the x=0.72 sample and lithium intercalation into both octahedral and tetrahedral sites in the SVO lattice, and that most but not all of the Ag (I) is reduced prior to initiation of V(V) reduction. Vanadium-51 NMR studies of SVO and lithiated SVO show decreased crystallinity with increased lithiation, as previously reported. Silver XAS studies indicate the formation of metallic silver crystallites in all the lithiated samples. A comparison of X-ray absorption near edge spectroscopy spectra for vanadium in these samples with those of reference compounds shows that some reduction of vanadium (V) occurs in the lithiated SVO with x=0.72 and increases with further lithiation leading to the formation of V(IV) and V(III) species. The results of this study indicate that vanadium(V) reduction occurs in parallel with silver (I) reduction during the initial stages of SVO lithiation, leading ultimately to the formation of vanadium (IV) and (III) species with further lithiation.

  17. The effect of external magnetic field on the bremsstrahlung nonlinear absorption mechanism in the interaction of high intensity short laser pulse with collisional underdense plasma

    SciTech Connect

    Sedaghat, M.; Ettehadi-Abari, M.; Shokri, B. Ghorbanalilu, M.

    2015-03-15

    Laser absorption in the interaction between ultra-intense femtosecond laser and solid density plasma is studied theoretically here in the intensity range Iλ{sup 2}≃10{sup 14}−10{sup 16}Wcm{sup −2}μm{sup 2}. The collisional effect is found to be significant when the incident laser intensity is less than 10{sup 16}Wcm{sup −2}μm{sup 2}. In the current work, the propagation of a high frequency electromagnetic wave, for underdense collisional plasma in the presence of an external magnetic field is investigated. It is shown that, by considering the effect of the ponderomotive force in collisional magnetized plasmas, the increase of laser pulse intensity leads to steepening of the electron density profile and the electron bunches of plasma makes narrower. Moreover, it is found that the wavelength of electric and magnetic fields oscillations increases by increasing the external magnetic field and the density distribution of electrons also grows in comparison with the unmagnetized collisional plasma. Furthermore, the spatial damping rate of laser energy and the nonlinear bremsstrahlung absorption coefficient are obtained in the collisional regime of magnetized plasma. The other remarkable result is that by increasing the external magnetic field in this case, the absorption coefficient increases strongly.

  18. Enhancement of conduction noise absorption by hybrid absorbers composed of indium-tin-oxide thin film and magnetic composite sheet on a microstrip line

    SciTech Connect

    Kim, Sun-Hong; Kim, Sung-Soo

    2014-05-05

    In order to develop wide-band noise absorbers with a focused design for low frequency performance, this study investigates hybrid absorbers that are composed of conductive indium-tin-oxide (ITO) thin film and magnetic composite sheets. The ITO films prepared via reactive sputtering exhibit a typical value of electrical resistivity of ≃10{sup −4} Ω m. Rubber composites with flaky Fe-Si-Al particles are used as the magnetic sheet with a high permeability and high permittivity. For the ITO film with a low surface resistance and covered by the magnetic sheet, approximately 90% power absorption can be obtained at 1 GHz, which is significantly higher than that of the original magnetic sheet or ITO film. The high power absorption of the hybrid absorber is attributed to the enhanced ohmic loss of the ITO film through increased electric field strength bounded by the upper magnetic composite sheet. However, for the reverse layering sequence of the ITO film, the electric field experienced by ITO film is very weak due to the electromagnetic shielding by the under layer of magnetic sheet, which does not result in enhanced power absorption.

  19. X-ray absorption spectroscopy studies on magnetic tunnel junctions with AlO and AlN tunnel barriers

    SciTech Connect

    Mun, B. S.; Moon, J. C.; Hong, S. W.; Kang, K. S.; Kim, K.; Kim, T. W.; Ju, H. L.

    2006-04-15

    X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) measurements of the optimized magnetic tunnel junctions (MTJs) with AlO and AlN barriers have been performed to study the chemical structures of the barrier and the underlying layer. These MTJs with AlO and AlN barriers exhibited increased tunneling magnetoresistance (TMR) after annealing at 200 deg. C from 27% to 45% and from 25% to 33%, respectively. Surprisingly, the XPS and XAS measurements confirmed that both the as-grown and the annealed MTJs had metallic Co and Fe at the interface between the barrier and the underlying CoFe layer. After annealing, under-stoichiometric AlO{sub x} and AlN{sub x} phases in MTJs with AlO and AlN barriers partially transformed into stoichiometric Al{sub 2}O{sub 3} and AlN phases, respectively. Thus the increase in TMR after annealing for MTJs with clean interface between the barrier and the underlying layer is believed due to the anion redistribution inside the barrier layer, not from back diffusion from pinned magnetic layer to barrier layer.

  20. Enhancement in treatment planning for magnetic nanoparticle hyperthermia: optimization of the heat absorption pattern.

    PubMed

    Salloum, M; Ma, R; Zhu, L

    2009-06-01

    In clinical applications of magnetic nanoparticle hyperthermia for cancer treatment it is very important to ensure a maximum damage to the tumor while protecting the normal tissue. The resultant heating pattern by the nanoparticle distribution in tumor is closely related to the injection parameters. In this study we develop an optimization algorithm to inversely determine the optimum heating patterns induced by multiple nanoparticle injections in tumor models with irregular geometries. The injection site locations, thermal properties of tumor and tissue, and local blood perfusion rates are used as inputs to the algorithm to determine the optimum parameters of the heat sources for all nanoparticle injection sites. The design objective is to elevate the temperature of at least 90% of the tumor above 43 degrees C, and to ensure only less than 10% of the normal tissue is heated to temperatures of 43 degrees C or higher. The efficiency, flexibility and capability of this approach have been demonstrated in a case study of two tumors with simple or complicated geometry. An extensive experimental database should be developed in the future to relate the optimized heating pattern parameters found in this study to their appropriate nanoparticle concentration, injection amount, and injection rate. We believe that the optimization algorithm developed in this study can be used as a guideline for physicians to design an optimal treatment plan in magnetic nanoparticle hyperthermia.

  1. Influence of protein environment on magnetic circular dichroism spectral properties of ferric and ferrous ligand complexes of yeast cytochrome c peroxidase.

    PubMed

    Pond, A E; Sono, M; Elenkova, E A; Goodin, D B; English, A M; Dawson, J H

    1999-01-01

    The addition of exogenous ligands to the ferric and ferrous states of yeast cytochrome c peroxidase (CCP) is investigated with magnetic circular dichroism (MCD) at 4 degrees C to determine the effect the protein environment may exercise on spectral properties. The MCD spectrum of each derivative is directly compared to those of analogous forms of horseradish peroxidase (HRP) and myoglobin (Mb), two well-characterized histidine-ligated heme proteins. The ferric azide adduct of CCP is a hexacoordinate, largely low-spin species with an MCD spectrum very similar to that of ferric azide HRP. This complex displays an MCD spectrum dissimilar from that of the Mb derivative, possibly because of the stabilizing interaction between the azide ligand and the distal arginine of CCP (Arg 48). For the ferric fluoride derivative all three proteins display varied MCD data, indicating that the differences in the distal pocket of each protein influences their respective MCD characteristics. The MCD data for the cyanoferric complexes are similar for all three proteins, demonstrating that a strong field ligand bound in the sixth axial position dominates the MCD characteristics of the derivative. Similarly, the ferric NO complexes of the three proteins show MCD spectra similar in feature position and shape, but vary somewhat in intensity. Reduction of CCP at neutral pH yields a typical pentacoordinate high-spin complex with an MCD spectrum similar to that of deoxyferrous HRP. Formation of the NO and cyanide complexes of ferrous CCP gives derivatives with MCD spectra similar to the analogous forms of HRP and Mb in both feature position and shape. Addition of CO to deoxyferrous CCP results in a ferrous-CO complex with MCD spectral similarity to that of ferrous-CO HRP but not Mb, indicating that interactions between the ligand and the distal residues affects the MCD characteristics. Examination of alkaline (pH 9.7) deoxyferrous CCP indicates that a pH dependent conformational change has

  2. Itinerant ferromagnetism in the As 4p conduction band of Ba0.6K0.4Mn2As2 identified by x-ray magnetic circular dichroism

    SciTech Connect

    Ueland, B. G.; Pandey, Abhishek; Lee, Y.; Sapkota, A.; Choi, Y.; Haskel, D.; Rosenberg, R. A.; Lang, J. C.; Harmon, B. N.; Johnston, D. C.; Kreyssig, A.; Goldman, A. I.

    2015-05-27

    In this study, x-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba0.6K0.4Mn2As2 show that the ferromagnetism below TC ≈ 100 K arises in the As 4p conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below TC, however, a clear XMCD signal is found at the As K edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic c axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that the previously reported itinerant ferromagnetism is associated with the As 4p conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.

  3. Novel ion imprinted magnetic mesoporous silica for selective magnetic solid phase extraction of trace Cd followed by graphite furnace atomic absorption spectrometry detection

    NASA Astrophysics Data System (ADS)

    Zhao, Bingshan; He, Man; Chen, Beibei; Hu, Bin

    2015-05-01

    Determination of trace Cd in environmental, biological and food samples is of great significance to toxicological research and environmental pollution monitoring. While the direct determination of Cd in real-world samples is difficult due to its low concentration and the complex matrix. Herein, a novel Cd(II)-ion imprinted magnetic mesoporous silica (Cd(II)-II-MMS) was prepared and was employed as a selective magnetic solid-phase extraction (MSPE) material for extraction of trace Cd in real-world samples followed by graphite furnace atomic absorption spectrometry (GFAAS) detection. Under the optimized conditions, the detection limit of the proposed method was 6.1 ng L- 1 for Cd with the relative standard deviation (RSD) of 4.0% (c = 50 ng L- 1, n = 7), and the enrichment factor was 50-fold. To validate the proposed method, Certified Reference Materials of GSBZ 50009-88 environmental water, ZK018-1 lyophilized human urine and NIES10-b rice flour were analyzed and the determined values were in a good agreement with the certified values. The proposed method exhibited a robust anti-interference ability due to the good selectivity of Cd(II)-II-MMS toward Cd(II). It was successfully employed for the determination of trace Cd(II) in environmental water, human urine and rice samples with recoveries of 89.3-116%, demonstrating that the proposed method has good application potential in real world samples with complex matrix.

  4. Kinetic (particle-in-cell) simulation of nonlinear laser absorption in a finite-size plasma with a background inhomogeneous magnetic field

    SciTech Connect

    Mehdian, H. Kargarian, A.; Hajisharifi, K.

    2015-06-15

    In this paper, the effect of an external inhomogeneous magnetic field on the high intensity laser absorption rate in a sub-critical plasma has been investigated by employing a relativistic electromagnetic 1.5 dimensional particle-in-cell code. Relying on the effective nonlinear phenomena such as phase-mixing and scattering, this study shows that in a finite-size plasma the laser absorption increases with inhomogeneity of the magnetic field (i.e., reduction of characteristic length of inhomogeneous magnetic field, λ{sub p}) before exiting a considerable amount of laser energy from the plasma due to scattering process. On the other hand, the presence of the external inhomogeneous magnetic field causes the maximum absorption of laser to occur at a shorter time. Moreover, study of the kinetic results associated with the distribution function of plasma particles shows that, in a special range of the plasma density and the characteristic length of inhomogeneous magnetic field, a considerable amount of laser energy is transferred to the particles producing a population of electrons with kinetic energy along the laser direction.

  5. Calculated Hanle transmission and absorption spectra of the {sup 87}Rb D{sub 1} line with residual magnetic field for arbitrarily polarized light

    SciTech Connect

    Noh, Heung-Ryoul; Moon, Han Seb

    2010-09-15

    This paper reports a theoretical study on the transmission spectra of an arbitrarily polarized laser beam through a rubidium cell with or without a buffer gas in Hanle-type coherent population trapping (CPT). This study examined how laser polarization, transverse magnetic field, and collisions with buffer gas affects the spectrum. The transmission spectrum due to CPT and the absorption spectrum due to the level crossing absorption (LCA) were calculated according to the laser polarization. The results show that the LCA is strongly dependent on the transverse magnetic field and interaction time of the atoms with a laser light via collisions with the buffer gas. In addition, the spectral shape of the calculated Hanle spectrum is closely related to the direction between the (stray) transverse magnetic field and polarization of the laser.

  6. Additional ECR heating of a radially inhomogeneous plasma via the absorption of satellite harmonics of the surface flute modes in a rippled magnetic field

    SciTech Connect

    Girka, V. O.; Girka, I. O.

    2006-12-15

    A theoretical study is made of the possibility of additional heating of a radially inhomogeneous plasma in confinement systems with a rippled magnetic field via the absorption of satellite harmonics of the surface flute modes with frequencies below the electron gyrofrequency in the local resonance region, {epsilon}{sub 1} (r{sub 1}) = [2{pi}c/({omega}L)]{sup 2}, where {epsilon}{sub 1} is the diagonal element of the plasma dielectric tensor in the hydrodynamic approximation, L is the period of a constant external rippled magnetic field, and the radical coordinate r{sub 1} determines the position of the local resonance. It is found that the high-frequency power absorbed near the local resonance is proportional to the square of the ripple amplitude of the external magnetic field. The mechanism proposed is shown to ensure the absorption of the energy of surface flute modes and, thereby, the heating of a radially inhomogeneous plasma.

  7. Gauge-Invariant Formulation of Circular Dichroism.

    PubMed

    Raimbault, Nathaniel; de Boeij, Paul L; Romaniello, Pina; Berger, J A

    2016-07-12

    Standard formulations of magnetic response properties, such as circular dichroism spectra, are plagued by gauge dependencies, which can lead to unphysical results. In this work, we present a general gauge-invariant and numerically efficient approach for the calculation of circular dichroism spectra from the current density. First we show that in this formulation the optical rotation tensor, the response function from which circular dichroism spectra can be obtained, is independent of the origin of the coordinate system. We then demonstrate that its trace is independent of the gauge origin of the vector potential. We also show how gauge invariance can be retained in practical calculations with finite basis sets. As an example, we explain how our method can be applied to time-dependent current-density-functional theory. Finally, we report gauge-invariant circular dichroism spectra obtained using the adiabatic local-density approximation. The circular dichroism spectra we thus obtain are in good agreement with experiment. PMID:27295541

  8. Water vapor absorption in porous media polluted by calcium nitrate studied by time domain nuclear magnetic resonance.

    PubMed

    Gombia, Mirko; Bortolotti, Villiam; Brown, Robert J S; Camaiti, Mara; Cavallero, Luisa; Fantazzini, Paola

    2009-08-01

    Nuclear magnetic resonance relaxation analysis of liquid water (1)H nuclei in real porous media, selected for their similar composition (carbonate rocks) and different pore space architecture, polluted with calcium nitrate, is presented to study the kinetics of water condensation and salt deliquescence inside the pore space. These phenomena are responsible for deterioration of porous materials when exposed to environmental injury by pollution in a humid atmosphere. The theory is well described for simple pore geometries, but it is not yet well understood in real porous media with wide distributions of pore sizes and connections. The experiment is performed by following in time the formation of liquid water inside the pore space by T(1) and T(2) relaxation time distributions. The distributions allow one to see the effects of both the salt concentration and the pore space structure on the amount of water vapor condensed and its kinetics. It is shown that, for a given lithotype, even with different amounts of pollutant, the rate-average relaxation time T(1ra) tends to increase monotonically with NMR signal, proportional to the amount of liquid water. T(1ra) is often inversely associated with surface-to-volume ratio. This suggests a trend toward the filling of larger pores as amounts of liquid water increase, but it does not indicate a strict sequential filling of pores in order of size and starting with the smallest; in fact, relaxation time distributions show clearly that this is not the case. Increased amounts of salt lead to both markedly increased rates and markedly increased amounts of water absorption. NMR measurements of amounts of water, together with relaxation time distributions, give the possibility of information on the effect of pollution in porous materials exposed to humid atmospheres but sheltered from liquid water, even before the absorption of large amounts of moisture and subsequent damage. These phenomena are of importance also in other fields

  9. Water vapor absorption in porous media polluted by calcium nitrate studied by time domain nuclear magnetic resonance.

    PubMed

    Gombia, Mirko; Bortolotti, Villiam; Brown, Robert J S; Camaiti, Mara; Cavallero, Luisa; Fantazzini, Paola

    2009-08-01

    Nuclear magnetic resonance relaxation analysis of liquid water (1)H nuclei in real porous media, selected for their similar composition (carbonate rocks) and different pore space architecture, polluted with calcium nitrate, is presented to study the kinetics of water condensation and salt deliquescence inside the pore space. These phenomena are responsible for deterioration of porous materials when exposed to environmental injury by pollution in a humid atmosphere. The theory is well described for simple pore geometries, but it is not yet well understood in real porous media with wide distributions of pore sizes and connections. The experiment is performed by following in time the formation of liquid water inside the pore space by T(1) and T(2) relaxation time distributions. The distributions allow one to see the effects of both the salt concentration and the pore space structure on the amount of water vapor condensed and its kinetics. It is shown that, for a given lithotype, even with different amounts of pollutant, the rate-average relaxation time T(1ra) tends to increase monotonically with NMR signal, proportional to the amount of liquid water. T(1ra) is often inversely associated with surface-to-volume ratio. This suggests a trend toward the filling of larger pores as amounts of liquid water increase, but it does not indicate a strict sequential filling of pores in order of size and starting with the smallest; in fact, relaxation time distributions show clearly that this is not the case. Increased amounts of salt lead to both markedly increased rates and markedly increased amounts of water absorption. NMR measurements of amounts of water, together with relaxation time distributions, give the possibility of information on the effect of pollution in porous materials exposed to humid atmospheres but sheltered from liquid water, even before the absorption of large amounts of moisture and subsequent damage. These phenomena are of importance also in other fields

  10. Characterization of Circular RNAs.

    PubMed

    Zhang, Yang; Yang, Li; Chen, Ling-Ling

    2016-01-01

    Accumulated lines of evidence reveal that a large number of circular RNAs are produced in transcriptomes from fruit fly to mouse and human. Unlike linear RNAs shaped with 5' cap and 3' tail, circular RNAs are characterized by covalently closed loop structures without open terminals, thus requiring specific treatments for their identification and validation. Here, we describe a detailed pipeline for the characterization of circular RNAs. It has been successfully applied to the study of circular intronic RNAs derived from intron lariats (ciRNAs) and circular RNAs produced from back spliced exons (circRNAs) in human. PMID:26721494

  11. Circular Dammann grating

    NASA Astrophysics Data System (ADS)

    Zhou, Changhe; Jia, Jia; Liu, Liren

    2003-11-01

    A circular Dammann grating that can produce circular equal intensities at various orders in the far field is described. A set of parameters such as order, circular number, uniformity, and diffraction efficiency has been defined to describe the novel diffractive phase elements. Numerical solutions of binary-phase (0, π) circular Dammann gratings are given. The results of experiments with a four-order circular Dammann grating made by a lithographic technique are presented. This novel diffractive optical element should be highly interesting in a wide variety of practical applications.

  12. Magnetic and microwave absorption properties of self-assemblies composed of core-shell cobalt-cobalt oxide nanocrystals.

    PubMed

    Wang, Zhongzhu; Bi, Hong; Wang, Peihong; Wang, Min; Liu, Zhiwei; Shen, Lei; Liu, Xiansong

    2015-02-01

    Core-shell structure cobalt-cobalt oxide nanocomposites were directly synthesized via annealing Co nanocrystals in air at 300 °C. Their microstructure and magnetic properties were characterized by XRD, TEM, XPS and VSM, respectively. The microwave absorbing properties of the nanocomposite powders by dispersing them in wax were investigated in the 2-18 GHz frequency range. The sample that was annealed for 1 h exhibits the maximum reflection loss of -30.5 dB and a bandwidth of less than -10 dB covering the 12.6-17.3 GHz range with the coating thickness of only 1.7 mm. At the same thickness, the sample annealed for 3 h exhibits the maximum reflection loss of -24 dB and a bandwidth that almost covers the whole X-band (8-11.5 GHz). With increase in the insulating cobalt oxide shell, the enhanced permeability could contribute to the decrease of eddy current loss, and the permittivity could be easily adjusted; thus, the microwave absorption properties of the cobalt oxide nanocrystals could be easily adjusted. PMID:25559407

  13. Dynamics of intramolecular electron transfer reaction of FAD studied by magnetic field effects on transient absorption spectra.

    PubMed

    Murakami, Masaaki; Maeda, Kiminori; Arai, Tatsuo

    2005-07-01

    The kinetics of intermediates generated from intramolecular electron-transfer reaction by photo irradiation of the flavin adenine dinucleotide (FAD) molecule was studied by a magnetic field effect (MFE) on transient absorption (TA) spectra. Existence time of MFE and MFE action spectra have a strong dependence on the pH of solutions. The MFE action spectra have indicated the existence of interconversion between the radical pair and the cation form of the triplet excited state of flavin part. All rate constants of the triplet and the radical pair were determined by analysis of the MFE action spectra and decay kinetics of TA. The obtained values for the interconversion indicate that the formation of cation radical promotes the back electron-transfer reaction to the triplet excited state. Further, rate constants of spin relaxation and recombination have been studied by the time profiles of MFE at various pH. The drastic change of those two factors has been obtained and can be explained by SOC (spin-orbit coupling) induced back electron-transfer promoted by the formation of a stacking conformation at pH > 2.5.

  14. Room Temperature Magnetic Barrier Layers in Magnetic Tunnel Junctions

    SciTech Connect

    Nelson-Cheeseman, B. B.; Wong, F. J.; Chopdekar, R. V.; Arenholz, E.; Suzuki, Y.

    2010-03-09

    We investigate the spin transport and interfacial magnetism of magnetic tunnel junctions with highly spin polarized LSMO and Fe3O4 electrodes and a ferrimagnetic NiFe2O4 (NFO) barrier layer. The spin dependent transport can be understood in terms of magnon-assisted spin dependent tunneling where the magnons are excited in the barrier layer itself. The NFO/Fe3O4 interface displays strong magnetic coupling, while the LSMO/NFO interface exhibits clear decoupling as determined by a combination of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. This decoupling allows for distinct parallel and antiparallel electrode states in this all-magnetic trilayer. The spin transport of these devices, dominated by the NFO barrier layer magnetism, leads to a symmetric bias dependence of the junction magnetoresistance at all temperatures.

  15. Home Sewage Disposal. Special Circular 212.

    ERIC Educational Resources Information Center

    Wooding, N. Henry

    This circular provides current information for homeowners who must repair or replace existing on-lot sewage disposal systems. Site requirements, characteristics and preparation are outlined for a variety of alternatives such as elevated sand mounds, sand-lined beds and trenches, and oversized absorption area. Diagrams indicating construction…

  16. Imaging magnetic structures with a transmission X-ray microscope

    NASA Astrophysics Data System (ADS)

    Fischer, P.; Eimüller, T.; Schütz, G.; Guttmann, P.; Schmahl, G.; Bayreuther, G.

    2000-05-01

    The X-ray magnetic circular dichroism (X-MCD), i.e., the dependence of the absorption of circularly polarized X-rays on the magnetization of the absorber exhibits at L-edges of transition metals values up to 25%. This can serve as a huge magnetic contrast mechanism in combination with a transmission X-ray microscope (TXM) to image magnetic domains providing a lateral resolution down to about 30 nm. The inherent element-specificity, the possibility to record images in varying external fields within a complete hysteresis loop, the relation of the contrast to local magnetic spin and orbital moments, etc. demonstrate the unique applicability to study the magnetic domain structure in current technical relevant systems like magneto-optics for high density storage media, multilayers for GMR applications or nanostructures for MRAM technology.

  17. Renormalization Group Approach to the X-Ray Absorption Problem and Application to the Vigman-Finkelshtein Model for Magnetic Impurities in Metals.

    NASA Astrophysics Data System (ADS)

    Nunes de Oliveira, Luiz

    The renormalization group techniques developed by Wilson for the Kondo problem are applied to three related problems: the absorption of x-rays by metals, the absorption of x-rays by impurities in metals, and the specific heat of dilute magnetic alloys. In the first problem considered, the x-ray absorption problem, the metal is represented by a half-filled conduction band and a deep level representing a core state. The absorption of an x-ray photon excites an electron from this core level to the conduction band creating a core hole whose positive charge interacts with the conduction electrons. The absorption spectrum is, for the first time, calculated in the energy range 10('-10)D < (omega)-(omega)(,T) < D, where (omega) and (omega)(,T) are the x-ray and threshold frequencies, respectively, and D is the conduction bandwidth. For (omega)-(omega)(,T) < 10('-9)D, the absorption spectrum (mu)((omega)) is described by a power law (mu)(,o) {((omega) -(omega)(,T))/D}('-(alpha)) whose exponent (alpha) agrees with that of the Nozieres-De Dominicis asymptotic (i.e., valid in the limit (omega) (--->) (omega)(,T)) expression to seven decimal places; the prefactor (mu)(,o) is calculated for the first time. For (omega)-(omega)(,T) (TURNEQ) D, remarkably small deviations (e.g., deviations of 15% for (omega)-(omega)(,T) = .3D) from the Nozieres-De Dominicis power law are found. As a second application of the renormalization group techniques, the x-ray absorption spectrum for the resonant level model for impurities in metals is calculated. In this model, the metal is represented by a half-filled conduction band and the impurity by two levels: a core level from which an electron is excited to the conduction band by the absorption of an x-ray photon, and a resonant level, coupled to the conduction electrons, whose energy is lowered by the interaction with the core hole created by the absorption of the x-ray. In the x-ray absorption process, the resonant level is thus shifted to lower

  18. Theoretical and experimental study of high-magnetic-field XMCD spectra at the L2,3 absorption edges of mixed-valence rare-earth compounds

    NASA Astrophysics Data System (ADS)

    Kotani, Akio; Matsuda, Yasuhiro H.; Nojiri, Hiroyuki

    2009-11-01

    X-ray magnetic circular dichroism(XMCD) spectra at the L2,3 edges of mixed-valence rare-earth compounds in high magnetic fields are studied both theoretically and experimentally. The theoretical study is based on a new framework proposed recently by Kotani. The Zeeman splitting of 4f states, the mixed-valence character of 4f states, and the 4f-5d exchange interaction are incorporated into a single impurity Anderson model. New XMCD experiments in high magnetic fields up to 40 T are carried out for the mixed-valence compounds EuNi2(Si0.18Ge0.82)2 and YbInCu4 by using a miniature pulsed magnet, which was developed recently by Matsuda et al. The XMCD data are taken at 5 K by transmission measurements for incident X-rays with ± helicities at BL39XU in SPring-8. After giving a survey on recent developments in the theory of XMCD spectra for mixed-valence Ce and Yb compounds, we calculate the XMCD spectra of YbInCu4 at the field-induced valence transition around 32 T by applying the recent theoretical framework and by newly introducing at 32 T a discontinuous change in the Yb 4f level and that in the hybridization strength between the Yb 4f and conduction electrons. The calculated results are compared with the experimental ones.

  19. Magnetic Spinner

    ERIC Educational Resources Information Center

    Ouseph, P. J.

    2006-01-01

    A science toy sometimes called the "magnetic spinner" is an interesting class demonstration to illustrate the principles of magnetic levitation. It can also be used to demonstrate Faraday's law and a horizontally suspended physical pendulum. The levitated part contains two circular magnets encased in a plastic housing. Each magnet stays…

  20. X-ray magnetic circular dichroism for Co{sub x}Fe{sub 4−x}N (x = 0, 3, 4) films grown by molecular beam epitaxy

    SciTech Connect

    Ito, Keita; Sanai, Tatsunori; Yasutomi, Yoko; Toko, Kaoru; Suemasu, Takashi; Zhu, Siyuan; Kimura, Akio; Takeda, Yukiharu; Saitoh, Yuji

    2014-05-07

    We evaluated orbital (m{sub orb}) and spin magnetic moments (m{sub spin}) of Co{sub x}Fe{sub 4−x}N (x = 0, 3, 4) epitaxial thin films grown by molecular beam epitaxy using x-ray magnetic circular dichroism, and discussed the dependence of these values on x. Site-averaged m{sub spin} value of Fe atoms was deduced to be 1.91 μ{sub B} per atom, and that of Co atoms to be 1.47 μ{sub B} per atom in Co{sub 3}FeN at 300 K. These values are close to 1.87 μ{sub B} per Fe atom in Fe{sub 4}N and 1.43 μ{sub B} per Co atom in Co{sub 4}N, respectively. This result implies that the Fe and Co atoms in the Co{sub 3}FeN films were located both at corner and face-centered sites in the anti-perovskite lattice. Spin magnetic moments per unit cell were decreased linearly with increasing x in Co{sub x}Fe{sub 4−x}N. This tendency is in good agreement with theory predicted by the first-principle calculation.

  1. On the stability of self-consistent large amplitude waves in a cold plasma. I - Transverse circularly polarized waves in the absence of a large scale magnetic field

    NASA Technical Reports Server (NTRS)

    Lee, M. A.; Lerche, I.

    1978-01-01

    It is demonstrated that a self-consistent circularly polarized wave in an otherwise field-free homogeneous cold plasma is unstable to small amplitude perturbations. For either an electron-positron plasma or an electron-proton plasma the instability rate is at least about the order of the effective plasma frequency when the bulk flow speed is zero. For finite bulk flow speeds of the plasma, it is shown that the electron-positron plasma is unstable, again with a growth rate of the order of the effective plasma frequency; it is also shown that the electron-proton plasma is unstable (at least at small wave numbers, k) with a growth rate proportional to k. The calculated instability rates are conservative, for other modes not investigated here may be more unstable. The results of these calculations bear directly on the understanding of plasma systems thought to be driven by large amplitude waves.

  2. Vibronic Coupling Explains the Different Shape of Electronic Circular Dichroism and of Circularly Polarized Luminescence Spectra of Hexahelicenes.

    PubMed

    Liu, Yanli; Cerezo, Javier; Mazzeo, Giuseppe; Lin, Na; Zhao, Xian; Longhi, Giovanna; Abbate, Sergio; Santoro, Fabrizio

    2016-06-14

    We present the simulation of the absorption (ABS), electronic circular dichroism (ECD), emission (EMI), and circularly polarized luminescence (CPL) spectra for the weak electronic transition between the ground (S0) and the lowest excited state (S1) of hexahelicene, 2-methylhexahelicene, 2-bromohexahelicene, and 5-azahexahelicene. Vibronic contributions have been computed at zero Kelvin and at room temperature in harmonic approximation including Duschinsky effects and accounting for both Franck-Condon and Herzberg-Teller contributions. Our results nicely capture the effects of the different substituents on the experimental spectra. They also show that HT effects dominate the shape of ECD and CPL spectra where they even induce changes of signs; HT effects are also relevant in ABS and EMI, tuning the relative intensities of the different vibronic bands. HT effects are the main reason for the differences in the line shapes of ABS and ECD and of EMI and CPL spectra and for the mirror-symmetry breaking between ABS and EMI and between ECD and CPL spectra. In order to check the robustness of our results, given also that few examples of calculations of vibronic CPL spectra exist, we adopted both adiabatic and vertical approaches to define the model potential energy surfaces of the (S0) and the (S1) states; moreover we expanded the electric and magnetic dipole transition moments around both the S0 and S1 equilibrium geometries. PMID:27120334

  3. Electromagnetic waves reflection, transmission and absorption by graphene-magnetic semiconductor-graphene sandwich-structure in magnetic field: Faraday geometry

    NASA Astrophysics Data System (ADS)

    Kuzmin, Dmitry A.; Bychkov, Igor V.; Shavrov, Vladimir G.

    2014-11-01

    Electrodynamic properties of the graphene-magnetic semiconductor-graphene sandwich-structure have been investigated theoretically with taking into account the dissipation processes. Influence of graphene layers on electromagnetic waves propagation in graphene-semi-infinte magnetic semiconductor and graphene-magnetic semiconductor-graphene sandwich-structure has been analyzed. Frequency and field dependences of the reflectance, transmittance and absorbtance of electromagnetic waves by such structure have been calculated. The size effects associated with the thickness of the structure have been analyzed. The possibility of efficient control of electrodynamic properties of graphene-magnetic semiconductor-graphene sandwich-structure by an external magnetic field has been shown.

  4. Towards future circular colliders

    NASA Astrophysics Data System (ADS)

    Benedikt, Michael; Zimmermann, Frank

    2016-09-01

    The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) presently provides proton-proton collisions at a center-of-mass (c.m.) energy of 13 TeV. The LHC design was started more than 30 years ago, and its physics program will extend through the second half of the 2030's. The global Future Circular Collider (FCC) study is now preparing for a post-LHC project. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh) in a new ˜100 km tunnel. It also includes the design of a high-luminosity electron-positron collider (FCCee) as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3 S n superconductor, for the FCC-hh hadron collider, and a highly-efficient superconducting radiofrequency system for the FCC-ee lepton collider. Following the FCC concept, the Institute of High Energy Physics (IHEP) in Beijing has initiated a parallel design study for an e + e - Higgs factory in China (CEPC), which is to be succeeded by a high-energy hadron collider (SPPC). At present a tunnel circumference of 54 km and a hadron collider c.m. energy of about 70 TeV are being considered. After a brief look at the LHC, this article reports the motivation and the present status of the FCC study, some of the primary design challenges and R&D subjects, as well as the emerging global collaboration.

  5. Circular Data Images for Directional Data

    NASA Technical Reports Server (NTRS)

    Morpet, William J.

    2004-01-01

    Directional data includes vectors, points on a unit sphere, axis orientation, angular direction, and circular or periodic data. The theoretical statistics for circular data (random points on a unit circle) or spherical data (random points on a unit sphere) are a recent development. An overview of existing graphical methods for the display of directional data is given. Cross-over occurs when periodic data are measured on a scale for the measurement of linear variables. For example, if angle is represented by a linear color gradient changing uniformly from dark blue at -180 degrees to bright red at +180 degrees, the color image will be discontinuous at +180 degrees and -180 degrees, which are the same location. The resultant color would depend on the direction of approach to the cross-over point. A new graphical method for imaging directional data is described, which affords high resolution without color discontinuity from "cross-over". It is called the circular data image. The circular data image uses a circular color scale in which colors repeat periodically. Some examples of the circular data image include direction of earth winds on a global scale, rocket motor internal flow, earth global magnetic field direction, and rocket motor nozzle vector direction vs. time.

  6. Amide I vibrational circular dichroism of polypeptides: Generalized fragmentation approximation method

    NASA Astrophysics Data System (ADS)

    Choi, Jun-Ho; Kim, Joong-Soo; Cho, Minhaeng

    2005-05-01

    Fragment analyses of vibrational circular dichroic response of dipeptides were carried out recently [Choi and Cho, J. Chem. Phys. 120, 4383 (2004)]. In the present paper, by using a minimal size unit peptide containing two chiral carbons covalently bonded to the peptide group, a generalized fragmentation approximation method is discussed and applied to the calculations of infrared-absorption and vibrational circular dichroism (VCD) intensities of amide I vibrations in various secondary structure polypeptides. Unlike the dipole strength determining IR-absorption intensity, the rotational strength is largely determined by the cross terms that are given by the inner product between the transition electric dipole and the transition magnetic dipole of two different peptides. This explains why the signs and magnitudes of VCD peaks are far more sensitive to the relative orientation and distance between different peptide bonds in a given protein. In order to test the validity of fragmentation approximation, three different segments in a globular protein ubiquitin, i.e., right-handed α-helix, β-sheet, and β-turn regions, were chosen for density-functional theory (DFT) calculations of amide I vibrational properties and the numerically simulated IR-absorption and VCD spectra by using the fragmentation method are directly compared with DFT results. It is believed that the fragmentation approximation method will be of use in numerically simulating vibrational spectra of proteins in solutions.

  7. Circular polarization sensitive absorbers based on graphene

    PubMed Central

    Yang, Kunpeng; Wang, Min; Pu, Mingbo; Wu, Xiaoyu; Gao, Hui; Hu, Chenggang; Luo, Xiangang

    2016-01-01

    It is well known that the polarization of a linearly polarized (LP) light would rotate after passing through a single layer graphene under the bias of a perpendicular magnetostatic field. Here we show that a corresponding phase shift could be expected for circularly polarized (CP) light, which can be engineered to design the circular polarization sensitive devices. We theoretically validate that an ultrathin graphene-based absorber with the thickness about λ/76 can be obtained, which shows efficient absorption >90% within incident angles of ±80°. The angle-independent phase shift produced by the graphene is responsible for the nearly omnidirectional absorber. Furthermore, a broadband absorber in frequencies ranging from 2.343 to 5.885 THz with absorption over 90% is designed by engineering the dispersion of graphene. PMID:27034257

  8. Circular Intensity Differential Scattering of chiral molecules

    SciTech Connect

    Bustamante, C.J.

    1980-12-01

    In this thesis a theory of the Circular Intensity Differential Scattering (CIDS) of chiral molecules as modelled by a helix oriented with respect to the direction of incidence of light is presented. It is shown that a necessary condition for the existence of CIDS is the presence of an asymmetric polarizability in the scatterer. The polarizability of the scatterer is assumed generally complex, so that both refractive and absorptive phenomena are taken into account.

  9. Squaring a Circular Segment

    ERIC Educational Resources Information Center

    Gordon, Russell

    2008-01-01

    Consider a circular segment (the smaller portion of a circle cut off by one of its chords) with chord length c and height h (the greatest distance from a point on the arc of the circle to the chord). Is there a simple formula involving c and h that can be used to closely approximate the area of this circular segment? Ancient Chinese and Egyptian…

  10. Circular, confined distribution for charged particle beams

    DOEpatents

    Garnett, R.W.; Dobelbower, M.C.

    1995-11-21

    A charged particle beam line is formed with magnetic optics that manipulate the charged particle beam to form the beam having a generally rectangular configuration to a circular beam cross-section having a uniform particle distribution at a predetermined location. First magnetic optics form a charged particle beam to a generally uniform particle distribution over a square planar area at a known first location. Second magnetic optics receive the charged particle beam with the generally square configuration and affect the charged particle beam to output the charged particle beam with a phase-space distribution effective to fold corner portions of the beam toward the core region of the beam. The beam forms a circular configuration having a generally uniform spatial particle distribution over a target area at a predetermined second location. 26 figs.

  11. Circular, confined distribution for charged particle beams

    DOEpatents

    Garnett, Robert W.; Dobelbower, M. Christian

    1995-01-01

    A charged particle beam line is formed with magnetic optics that manipulate the charged particle beam to form the beam having a generally rectangular configuration to a circular beam cross-section having a uniform particle distribution at a predetermined location. First magnetic optics form a charged particle beam to a generally uniform particle distribution over a square planar area at a known first location. Second magnetic optics receive the charged particle beam with the generally square configuration and affect the charged particle beam to output the charged particle beam with a phase-space distribution effective to fold corner portions of the beam toward the core region of the beam. The beam forms a circular configuration having a generally uniform spatial particle distribution over a target area at a predetermined second location.

  12. Polyelectrolyte multilayers on magnetic silica as a new sorbent for the separation of trace copper in food samples and determination by flame atomic absorption spectrometry.

    PubMed

    Xiang, Guoqiang; Ma, Yulong; Jiang, Xiuming; Mao, Pu

    2014-12-01

    A novel magnetic silica sorbent with polyelectrolyte multilayers (PEMs) on its surface was prepared, and the sorbent was used for the magnetic solid phase extraction (MSPE) of trace Cu(2+) in drinking water with flame atomic absorption spectrometry (FAAS) as the detector. The experimental parameters for the MSPE procedure, such as the pH, desorption conditions, ultrasonic time and co-existing ions effects, were investigated. The adsorption capacity of the new sorbent was 14.7 mg g(-1) for Cu(2+). The detection limit of the developed method was 0.23 ng mL(-1) for Cu(2+) with an enrichment factor of 95.7. The analytical data obtained from the certified reference water and rice samples were in good agreement with the certified values. This method was also successfully applied to the determination of trace Cu(2+) in different food samples with satisfactory results.

  13. Magnetic, durable, and superhydrophobic polyurethane@Fe3O4@SiO2@fluoropolymer sponges for selective oil absorption and oil/water separation.

    PubMed

    Wu, Lei; Li, Lingxiao; Li, Bucheng; Zhang, Junping; Wang, Aiqin

    2015-03-01

    Magnetic, durable, and superhydrophobic polyurethane (PU) sponges were fabricated by chemical vapor deposition (CVD) of tetraethoxysilane (TEOS) to bind the Fe3O4 nanoparticles tightly on the sponge and then dip-coating in a fluoropolymer (FP) aqueous solution. The sponges were characterized using scanning electron microscopy and other analytical techniques. The effects of CVD time of TEOS and FP concentration on wettability, mechanical properties, oil absorbency, and oil/water selectivity of the sponges were also investigated. The sponges exhibit fast magnetic responsivity and excellent superhydrophobicity/superoleophilicity (CAwater = 157° and CAoil ≈ 0°). The sponges also show very high efficiency in oil/water separation and could, driven by a magnet, quickly absorb floating oils on the water surface and heavy oils under water. Moreover, the PU@Fe3O4@SiO2@FP sponges could be used as membranes for oil/water separation and for continuous separation of large amounts of oil pollutants from the water surface with the help of a pump. The in turn binding of Fe3O4 nanoparticles, SiO2, and FP can also improve mechanical properties of the PU sponge. The sponges maintain the superhydrophobicity even when they are stretched with 200% strain or compressed with 50% strain. The sponges also show excellent mechanical stability, oil stability, and reusability in terms of superhydrophobicity and oil absorbency. The magnetic, durable, and superhydrophobic PU sponges are very promising materials for practical oil absorption and oil/water separation. PMID:25671386

  14. Zeeman shift of two-dimensional optical signals of Mg-porphyrin dimers with circularly polarized beams

    PubMed Central

    Rodriguez, Justo J.; Mukamel, Shaul

    2012-01-01

    Two-dimensional (2D) electronic spectra of Mg-porphyrin dimers with circularly polarized laser pulses are simulated for two molecular geometries. The Zeeman shift of the non-chiral 2D spectra induced by a magnetic field highlights spectral regions that are dominated by exciton states with large total angular momentum, and are particularly sensitive to the geometry. These 2D shifts show much higher sensitivity to the molecular array than the absorption spectrum shifts. For different molecular geometries, only the intensity of the 2D spectrum peaks changes while the form of the Zeeman shifts in the 2D frequency space is modified. PMID:23206037

  15. Magnetic and microwave absorption properties of BaMgx/2Mnx/2CoxTi2xFe12-4xO19 hexaferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Shams Alam, Reza; Moradi, Mahmood; Nikmanesh, Hossein; Ventura, Joao; Rostami, Mohammad

    2016-03-01

    Substituted barium hexaferrite nanoparticles with nominal composition of BaMgx/2Mnx/2CoxTi2xFe12-4xO19 (x=0-0.5) were synthesized by a co-precipitation method. Then, the structural, magnetic and microwave characteristics of the representative samples were examined by employing X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). The XRD, along with FTIR evaluations confirmed the successful substitution of Mg, Mn, Co and Ti cations in the barium hexaferrite lattice. The microstructure evaluations also proved that the mean particle size decreases and typical morphologies are gradually varying from almost platelet (x=0) to irregular shapes (x=0.5) with increasing dopant concentration. Hysteresis loops revealed that the saturation magnetization increased up to substitution level of x=0.2, and then decreased abruptly. In addition, the coercivity exhibited a decreasing trend from 3669 Oe to 708 Oe with increasing amount of substitution. Finally, microwave measurement showed that the substituted barium hexaferrite sample with x=0.5 could be used as an efficient microwave absorption material with an appropriate absorption bandwidth of 6 GHz in the 10-16 GHz frequency range.

  16. Compact waveguide circular polarizer

    DOEpatents

    Tantawi, Sami G.

    2016-08-16

    A multi-port waveguide is provided having a rectangular waveguide that includes a Y-shape structure with first top arm having a first rectangular waveguide port, a second top arm with second rectangular waveguide port, and a base arm with a third rectangular waveguide port for supporting a TE.sub.10 mode and a TE.sub.20 mode, where the end of the third rectangular waveguide port includes rounded edges that are parallel to a z-axis of the waveguide, a circular waveguide having a circular waveguide port for supporting a left hand and a right hand circular polarization TE.sub.11 mode and is coupled to a base arm broad wall, and a matching feature disposed on the base arm broad wall opposite of the circular waveguide for terminating the third rectangular waveguide port, where the first rectangular waveguide port, the second rectangular waveguide port and the circular waveguide port are capable of supporting 4-modes of operation.

  17. Detection of circular polarization in light scattered from photosynthetic microbes

    PubMed Central

    Sparks, William B.; Hough, James; Germer, Thomas A.; Chen, Feng; DasSarma, Shiladitya; DasSarma, Priya; Robb, Frank T.; Manset, Nadine; Kolokolova, Ludmilla; Reid, Neill; Macchetto, F. Duccio; Martin, William

    2009-01-01

    The identification of a universal biosignature that could be sensed remotely is critical to the prospects for success in the search for life elsewhere in the universe. A candidate universal biosignature is homochirality, which is likely to be a generic property of all biochemical life. Because of the optical activity of chiral molecules, it has been hypothesized that this unique characteristic may provide a suitable remote sensing probe using circular polarization spectroscopy. Here, we report the detection of circular polarization in light scattered by photosynthetic microbes. We show that the circular polarization appears to arise from circular dichroism of the strong electronic transitions of photosynthetic absorption bands. We conclude that circular polarization spectroscopy could provide a powerful remote sensing technique for generic life searches. PMID:19416893

  18. Characterization of the Cu(Π) and Zn(Π) binding to the Amyloid-β short peptides by both the Extended X-ray Absorption Fine Structure and the Synchrotron Radiation Circular Dichroism spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiyin; Sun, Shuaishuai; Xu, Jianhua; Zhang, Jing; Huang, Yan; Zhang, Bingbing; Tao, Ye

    2013-04-01

    Alzheimer's disease (AD) is a progressive and devastating neurodegenerative pathology, clinically characterized by dementia, cognitive impairment, personality disorders and memory loss. It is generally accepted that, misfolding of Aβ peptides is the key element in pathogenesis and the secondary structure of Aβ can be changed to major β-strand with reasons unknown yet. Many studies have shown that the misfolding may be linked with some biometals, mainly copper and zinc ions. To characterize interactions of Aβ and metal ions, we utilized both the extended X-ray fine structure spectroscopy (EXAFS) and the synchrotron radiation circular dichroism spectroscopy (SRCD). Aβ (13-22), Aβ (13-21), Aβ (E22G) and Aβ(HH-AA) were selected to study the mechanism of copper and zinc binding to Aβ. We found that Cu interaction with H13 and H14 residues led to the disappearance of the PPΠ, while the Cu binding E22 residue caused a remarkable conformation change to β-sheet enrichment. The Zn ion, in contrast, made little effect on the conformation and it coordinated to only one histidine (H residue) or not.

  19. Structural, Magnetic, and Microwave-Absorption Properties of Nanocrystalline Ca(MnSn) x Fe12-2 x O19 Ferrites

    NASA Astrophysics Data System (ADS)

    Ali-Sharbati; Amiri, G. R.; Mousarezaei, R.

    2015-02-01

    Nanoparticles of Ca(MnSn) x Fe12-2 x O19 with x ranging from 0.00 to 0.6 in steps of 0.2 were prepared by use of the citrate precursor method. The structural, microwave-absorption, and magnetic properties of these ferrites were determined by use of different characterization techniques. The morphology of the ferrite powders was investigated by transmission electron microscopy (TEM). X-ray diffraction (XRD) was used for structural and micro-structural studies, and revealed that the samples had an M-type hexagonal structure. The crystallite size for each sample was calculated by use of the Scherrer formula for the most intense peak (411) and the results were compared with those obtained from TEM images of the samples. The particle size of the powder varied from 60 to 36 nm. Magnetic measurements were performed by vibrating sample magnetometry (VSM) at room temperature. The microwave-absorption properties of ferrite (70 wt.%)-polymer (30 wt.%) composites 2 mm thick were investigated by vector network analysis (VNA) in the frequency range 12-20 GHz. The ferrite for which x = 0.4 had a minimum reflection loss of -29 dB at 17.3 GHz with a -15 dB bandwidth over the extended frequency ranges 12.9-14.5 GHz and 16.7-18 GHz. The minimum loss reached -32 dB at frequency of 17 GHz when the total amount of Mn2+ and Sn4+ ions was 0.6. These results suggest that the synthesized magnetic composites can be used as effective microwave absorbers in military applications (radar cross-section reduction).

  20. Magnetic and microwave absorption properties of rare earth ions (Sm3+, Er3+) doped strontium ferrite and its nanocomposites with polypyrrole

    NASA Astrophysics Data System (ADS)

    Luo, Juhua; Xu, Yang; Mao, Hongkai

    2015-05-01

    M-type strontium ferrite substituted by RE (RE=Sm3+, Er3+) were prepared via a sol-gel method. Polypyrrole (PPy)/ferrite nanocomposites (with 20 wt% ferrite) were prepared by in situ polymerization method in the presence of ammonium persulfate. Effect of the substituted RE ions on structure, magnetic properties and microwave absorption properties were investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and vector network analyzer. All XRD patterns show the single phase of strontium hexaferrite without other intermediate phases. The crystallite size of synthesized particle is within the range of 22.2-38.1 nm. The structural in character of the composites were investigated with FT-IR analysis. It shows that the ferrite successfully packed by PPy. TEM photographs show that the particle size had grown up to 50-100 nm after coating with PPy. In the magnetization for the PPy/SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) composites, the coercivity (Hc) of the composites both increased compared with the undoped composite while the saturation magnetization (Ms) appeared opposite change with different RE ions. Considering the electromagnetic loss and impedance matching comprehensively, the Er-doped ferrite/PPy composite got the better microwave absorption performance with the maximum RL value of -24.01 dB in 13.8 GHz at 3.0 mm. And its width (<-10 dB) has reached 7.2 GHz which has covered the whole Ku band.

  1. Cold Rydberg atoms in circular states

    NASA Astrophysics Data System (ADS)

    Anderson, David; Schwarzkopf, Andrew; Raithel, Georg

    2012-06-01

    Circular-state Rydberg atoms are interesting in that they exhibit a unique combination of extraordinary properties; long lifetimes (˜n^5), large magnetic moments (l=|m|=n-1) and no first order Stark shift. Circular states have found applications in cavity quantum electrodynamics and precision measurements [1,2], among other studies. In this work we present the production of circular states in an atom trapping apparatus using an adiabatic state-switching method (the crossed-field method [3]). To date, we have observed lifetimes of adiabatically prepared states of several milliseconds. Their relatively large ionization electric fields have been verified by time-of-flight signatures of ion trajectories. We intend to explore the magnetic trapping of circular state Rydberg atoms, as well as their production and interaction properties in ultra-cold and degenerate samples.[4pt] [1] P. Bertet et al., Phys. Rev. Lett., 88, 14 (2002)[0pt] [2] M. Brune et al., Phys. Rev. Lett., 72, 21 (1994)[0pt] [3] D. Delande and J.C. Gay, Europhys. Lett., 5, 303-308 (1988).

  2. Ionic liquid-linked dual magnetic microextraction of lead(II) from environmental samples prior to its micro-sampling flame atomic absorption spectrometric determination.

    PubMed

    Yilmaz, Erkan; Soylak, Mustafa

    2013-11-15

    A novel and rapid microextraction approach termed as ionic liquid-linked dual magnetic microextraction (IL-DMME), was developed for the atomic absorption spectrometric determination of lead. The developed method based on a combination of dispersive liquid-liquid microextraction (DLLME) and dispersive micro solid-phase extraction (D-μ-SPE). In the first DLLME step, 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6], was selected to extract the lead-pyrrolidine-dithiocarbamate (Pb-PDC) complex from sample solution by the assistance of vortex agitator. After the first step, fifty milligrams of Fe3O4 magnetic nanoparticles (MNPs) were added to extraction of the ionic liquid and Pb-PDC complex in aqueous solution. The effective factors in proposed IL-DMME procedure, including volume of 1-butyl-3-methylimidazolium hexafluorophosphate, amount of Fe3O4 magnetic nanoparticles, vortex time, amount of ammonium pyrrolidinedithiocarbamate, sample volume and matrix effect were optimized in details. Under the optimal conditions, the method present has low detection limit (0.57 μg L(-1)), high preconcentration factor (160) and good repeatability (<7.5%, n=10). The accuracy of the developed method was evaluated by the analysis of the certified reference materials and addition-recovery tests. The method was successfully applied to the determination of lead in water, plant and hair samples.

  3. Ionic liquid-linked dual magnetic microextraction of lead(II) from environmental samples prior to its micro-sampling flame atomic absorption spectrometric determination.

    PubMed

    Yilmaz, Erkan; Soylak, Mustafa

    2013-11-15

    A novel and rapid microextraction approach termed as ionic liquid-linked dual magnetic microextraction (IL-DMME), was developed for the atomic absorption spectrometric determination of lead. The developed method based on a combination of dispersive liquid-liquid microextraction (DLLME) and dispersive micro solid-phase extraction (D-μ-SPE). In the first DLLME step, 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6], was selected to extract the lead-pyrrolidine-dithiocarbamate (Pb-PDC) complex from sample solution by the assistance of vortex agitator. After the first step, fifty milligrams of Fe3O4 magnetic nanoparticles (MNPs) were added to extraction of the ionic liquid and Pb-PDC complex in aqueous solution. The effective factors in proposed IL-DMME procedure, including volume of 1-butyl-3-methylimidazolium hexafluorophosphate, amount of Fe3O4 magnetic nanoparticles, vortex time, amount of ammonium pyrrolidinedithiocarbamate, sample volume and matrix effect were optimized in details. Under the optimal conditions, the method present has low detection limit (0.57 μg L(-1)), high preconcentration factor (160) and good repeatability (<7.5%, n=10). The accuracy of the developed method was evaluated by the analysis of the certified reference materials and addition-recovery tests. The method was successfully applied to the determination of lead in water, plant and hair samples. PMID:24148489

  4. A combined Mössbauer, magnetic circular dichroism, and density functional theory approach for iron cross-coupling catalysis: electronic structure, in situ formation, and reactivity of iron-mesityl-bisphosphines.

    PubMed

    Daifuku, Stephanie L; Al-Afyouni, Malik H; Snyder, Benjamin E R; Kneebone, Jared L; Neidig, Michael L

    2014-06-25

    While iron-bisphosphines have emerged as effective catalysts for C-C cross-coupling, the nature of the in situ formed iron species, elucidation of the active catalysts and the mechanisms of catalysis have remained elusive. A combination of (57)Fe Mössbauer and magnetic circular dichroism (MCD) spectroscopies of well-defined and in situ formed mesityl-iron(II)-SciOPP species combined with density functional theory (DFT) investigations provides the first direct insight into electronic structure, bonding and in situ speciation of mesityl-iron(II)-bisphosphines in the Kumada cross-coupling of MesMgBr and primary alkyl halides using FeCl2(SciOPP). Combined with freeze-trapped solution Mössbauer studies of reactions with primary alkyl halides, these studies demonstrate that distorted square-planar FeMes2(SciOPP) is the active catalyst for cross-coupling and provide insight into the molecular-level mechanism of catalysis. These studies also define the effects of key reaction protocol details, including the role of the slow Grignard addition method and the addition of excess SciOPP ligand, in leading to high product yields and selectivities. PMID:24918160

  5. Wiimote Experiments: Circular Motion

    ERIC Educational Resources Information Center

    Kouh, Minjoon; Holz, Danielle; Kawam, Alae; Lamont, Mary

    2013-01-01

    The advent of new sensor technologies can provide new ways of exploring fundamental physics. In this paper, we show how a Wiimote, which is a handheld remote controller for the Nintendo Wii video game system with an accelerometer, can be used to study the dynamics of circular motion with a very simple setup such as an old record player or a…

  6. Wiimote Experiments: Circular Motion

    NASA Astrophysics Data System (ADS)

    Kouh, Minjoon; Holz, Danielle; Kawam, Alae; Lamont, Mary

    2013-03-01

    The advent of new sensor technologies can provide new ways of exploring fundamental physics. In this paper, we show how a Wiimote, which is a handheld remote controller for the Nintendo Wii video game system with an accelerometer, can be used to study the dynamics of circular motion with a very simple setup such as an old record player or a bicycle wheel.

  7. Copyright Basics. Circular 1.

    ERIC Educational Resources Information Center

    Library of Congress, Washington, DC. Copyright Office.

    This circular answers some of the questions that are frequently asked about copyright, a form of protection provided by the laws of the United States to authors of "original works of authorship" including library, dramatic musical, artistic, and certain other intellectual works. The Copyright Act of 1976 (title 17 of the United States Code), which…

  8. Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Boccato, Silvia; Sanson, Andrea; Kantor, Innokenty; Mathon, Olivier; Dyadkin, Vadim; Chernyshov, Dmitry; Carnera, Alberto; Pascarelli, Sakura

    2016-09-01

    The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom. No thermal anomalies have been detected from the current XRD data. On the contrary, an intriguing thermal anomaly at about 150 K, ascribed to a stiffening of the Fe–Fe bonds, was found by EXAFS.

  9. Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Boccato, Silvia; Sanson, Andrea; Kantor, Innokenty; Mathon, Olivier; Dyadkin, Vadim; Chernyshov, Dmitry; Carnera, Alberto; Pascarelli, Sakura

    2016-09-01

    The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom. No thermal anomalies have been detected from the current XRD data. On the contrary, an intriguing thermal anomaly at about 150 K, ascribed to a stiffening of the Fe-Fe bonds, was found by EXAFS.

  10. Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction.

    PubMed

    Boccato, Silvia; Sanson, Andrea; Kantor, Innokenty; Mathon, Olivier; Dyadkin, Vadim; Chernyshov, Dmitry; Carnera, Alberto; Pascarelli, Sakura

    2016-09-01

    The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom. No thermal anomalies have been detected from the current XRD data. On the contrary, an intriguing thermal anomaly at about 150 K, ascribed to a stiffening of the Fe-Fe bonds, was found by EXAFS.

  11. Microwave absorption enhancement, magnetic coupling and ab initio electronic structure of monodispersed (Mn1-xCox)3O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhao, Pengfei; Liang, Chongyun; Gong, Xiwen; Gao, Ran; Liu, Jiwei; Wang, Min; Che, Renchao

    2013-08-01

    Monodispersed manganese oxide (Mn1-xCox)3O4 (0 <= x <= 0.5) nanoparticles, less than 10 nm size, are respectively synthesized via a facile thermolysis method at a rather low temperature, ranging from 90 to 100 °C, without any inertia gas for protection. The influences of the Co dopant content on the critical reaction temperature required for the nanoparticle formation, electronic band structures, magnetic properties, and the microwave absorption capability of (Mn1-xCox)3O4 are comprehensively investigated by means of both experimental and theoretical approaches including powder X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), super conductivity quantum interference device (SQUID) examination, and first-principle simulations. Co is successfully doped into the Mn atomic sites of the (Mn1-xCox)3O4 lattice, which is further confirmed by EELS data acquired from one individual nanoparticle. Therefore, continuous solid solutions of well-crystallized (Mn1-xCox)3O4 products are achieved without any impurity phase or phase separation. With increases in the Co dopant concentration x from 0 to 0.5, the lattice parameters change systemically, where the overall saturation magnetization at 30 K increases due to the more intense coupling of the 3d electrons between Mn and Co, as revealed by simulations. The microwave absorption properties of the (Mn1-xCox)3O4 nanoparticles are examined between 2 and 18 GHz. The maximum absorption peak -11.0 dB of the x = 0 sample is enhanced to -11.5 dB for x = 0.2, -12.7 dB for x = 0.25, -15.6 dB for x = 0.33, and -24.0 dB for x = 0.5 respectively, suggesting the Co doping effects. Our results might provide novel insights into the understanding of the influences of metallic ion doping on the electromagnetic properties of metallic oxide nanomaterials.Monodispersed manganese oxide (Mn1-xCox)3O4 (0 <= x <= 0.5) nanoparticles, less than 10 nm size, are respectively synthesized via a facile thermolysis method at a rather low

  12. [Guizhou planned parenthood circular].

    PubMed

    1980-05-29

    The Guizhou Provincial CCP Committee and the provinical people's government recently issued a circular on launching mass inspection of planned parenthood work throughout the province in late June. The inspection will look at whether or not the masses have been mobilized to pay serious attention to planned parenthood work, whether or not such education has been launched, what kind of concrete measures have been adopted, and what kind of concrete experiences have been learned. It will also include the implementation of birth control measures, the resolute prohibition on having a 3rd child, and the promotion of having only 1 child/couple. The circular urged the departments at all levels to strengthen their leadership over planned parenthood work, deepen investigation and study, continuously study the new situation and solve the new problems.

  13. Soft magnetic property and enhanced microwave absorption of nanoparticles of Co0.5Zn0.5Fe2O4 incorporated in MWCNT

    NASA Astrophysics Data System (ADS)

    Mallick, A.; Mahapatra, A. S.; Mitra, A.; Chakrabarti, P. K.

    2016-10-01

    Nanoparticles of Co0.5Zn0.5Fe2O4 (CZFO) are prepared by coprecipitation method where CoCl2·H2O, ZnCl2·6H2O and FeCl3 are used as precursor materials. To enhance the microwave absorption, nanoparticles of CZFO are incorporated in the matrix of multiwall carbon nanotubes (MWCNT). X-ray diffractogram (XRD) and its analysis confirmed the formation of the desired crystallographic phase of the sample. The average crystallite size is evaluated by using the Debye-Scherrer formula. Micrographs observed in high resolution transmission electron microscope confirm the successful incorporation of CZFO in the matrix of MWCNT. Results obtained from the high resolution lattice fringe and selected area electron diffraction patterns are in good agreement with the findings extracted from the XRD analysis. Analysis of Raman spectra confirms the presence of CZFO and MWCNT in the nanocomposite sample. Magnetic properties recorded in SQUID magnetometer confirm the presence of mixed state of superparamagnetic and ferrimagnetic nanoparticles. Reflection losses in X (8-12 GHz) and Ku (12-18 GHz) bands of microwave region are significantly high (~-38.2 dB at 16.9 GHz). High magnetization (~36.5 emu/g at 300 K), low coercive field (~30.1 Oe at 300 K) and high reflection loss of CZFO-MWCNT would be suitable for application in microwave devices.

  14. Preparation of modified magnetic nanoparticles as a sorbent for the preconcentration and determination of cadmium ions in food and environmental water samples prior to flame atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Mirabi, Ali; Dalirandeh, Zeinab; Rad, Ali Shokuhi

    2015-05-01

    A new method has been developed for the separation/preconcentration of trace level cadmium ions using diphenyl carbazone/sodium dodecyl sulfate immobilized on magnetic nanoparticle Fe3O4 as a new sorbent SPE and their determination by flame atomic absorption spectrometry (FAAS). Synthesized nanoparticle was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Various influencing parameters on the separation and preconcentration of trace level cadmium ions such as, pH value, amount of nanoparticles, amount of diphenyl carbazone, condition of eluting solution, the effects of matrix ions were examined. The cadmium ions can be eluted from the modified magnetic nanoparticle using 1 mol L-1 HCl as a desorption reagent. The detection limit of this method for cadmium was 3.71 ng ml-1 and the R.S.D. was 0.503% (n=6). The advantages of this new method include rapidity, easy preparation of sorbents and a high concentration factor. The proposed method has been applied to the determination of Cd ions at trace levels in real samples such as, green tea, rice, tobacco, carrot, lettuce, ginseng, spice, tap water, river water, sea water with satisfactory results.

  15. Magnetic stirrer induced dispersive ionic-liquid microextraction for the determination of vanadium in water and food samples prior to graphite furnace atomic absorption spectrometry.

    PubMed

    Naeemullah; Kazi, Tasneem Gul; Tuzen, Mustafa

    2015-04-01

    A new dispersive liquid-liquid microextraction, magnetic stirrer induced dispersive ionic-liquid microextraction (MS-IL-DLLME) was developed to quantify the trace level of vanadium in real water and food samples by graphite furnace atomic absorption spectrometry (GFAAS). In this extraction method magnetic stirrer was applied to obtained a dispersive medium of 1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6] in aqueous solution of (real water samples and digested food samples) to increase phase transfer ratio, which significantly enhance the recovery of vanadium - 4-(2-pyridylazo) resorcinol (PAR) chelate. Variables having vital role on desired microextraction methods were optimised to obtain the maximum recovery of study analyte. Under the optimised experimental variables, enhancement factor (EF) and limit of detection (LOD) were achieved to be 125 and 18 ng L(-1), respectively. Validity and accuracy of the desired method was checked by analysis of certified reference materials (SLRS-4 Riverine water and NIST SRM 1515 Apple leaves). The relative standard deviation (RSD) for 10 replicate determinations at 0.5 μg L(-1) of vanadium level was found to be <5.0%. This method was successfully applied to real water and acid digested food samples.

  16. Effect of Substitution of Mn, Cu, and Zr on the Structural, Magnetic, and Ku-Band Microwave-Absorption Properties of Strontium Hexaferrite Nanoparticles

    NASA Astrophysics Data System (ADS)

    Rostami, Mohammad; Moradi, Mahmood; Alam, Reza Shams; Mardani, Reza

    2016-08-01

    The ferrites with the compositions of SrMn x Cu x Zr2 x Fe(12-4 x)O19 ( x = 0.0, 0.2, 0.3, 0.4, and 0.5) are synthesized by the coprecipitation method. The formation of M-type hexaferrite is confirmed by x-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses. The morphology of the samples is shown by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) microscopy. Vibrating sample magnetometer (VSM) analysis has been used for the investigation of the magnetic properties, and the reason for the changes in the magnetic properties as a result of doping, are expressed. The values of coercivity decrease by increasing the amount of substitution, which could be related to the modification of anisotropy form the c-axis toward the c-plane. Finally, we have used vector network analysis to investigate the microwave absorption properties. We find that the samples with the composition of SrMn0.4Cu0.4Zr0.8Fe10.4O19 have the largest reflection loss and the widest bandwidth among these samples.

  17. Circular inferences in schizophrenia.

    PubMed

    Jardri, Renaud; Denève, Sophie

    2013-11-01

    A considerable number of recent experimental and computational studies suggest that subtle impairments of excitatory to inhibitory balance or regulation are involved in many neurological and psychiatric conditions. The current paper aims to relate, specifically and quantitatively, excitatory to inhibitory imbalance with psychotic symptoms in schizophrenia. Considering that the brain constructs hierarchical causal models of the external world, we show that the failure to maintain the excitatory to inhibitory balance results in hallucinations as well as in the formation and subsequent consolidation of delusional beliefs. Indeed, the consequence of excitatory to inhibitory imbalance in a hierarchical neural network is equated to a pathological form of causal inference called 'circular belief propagation'. In circular belief propagation, bottom-up sensory information and top-down predictions are reverberated, i.e. prior beliefs are misinterpreted as sensory observations and vice versa. As a result, these predictions are counted multiple times. Circular inference explains the emergence of erroneous percepts, the patient's overconfidence when facing probabilistic choices, the learning of 'unshakable' causal relationships between unrelated events and a paradoxical immunity to perceptual illusions, which are all known to be associated with schizophrenia. PMID:24065721

  18. Circular inferences in schizophrenia.

    PubMed

    Jardri, Renaud; Denève, Sophie

    2013-11-01

    A considerable number of recent experimental and computational studies suggest that subtle impairments of excitatory to inhibitory balance or regulation are involved in many neurological and psychiatric conditions. The current paper aims to relate, specifically and quantitatively, excitatory to inhibitory imbalance with psychotic symptoms in schizophrenia. Considering that the brain constructs hierarchical causal models of the external world, we show that the failure to maintain the excitatory to inhibitory balance results in hallucinations as well as in the formation and subsequent consolidation of delusional beliefs. Indeed, the consequence of excitatory to inhibitory imbalance in a hierarchical neural network is equated to a pathological form of causal inference called 'circular belief propagation'. In circular belief propagation, bottom-up sensory information and top-down predictions are reverberated, i.e. prior beliefs are misinterpreted as sensory observations and vice versa. As a result, these predictions are counted multiple times. Circular inference explains the emergence of erroneous percepts, the patient's overconfidence when facing probabilistic choices, the learning of 'unshakable' causal relationships between unrelated events and a paradoxical immunity to perceptual illusions, which are all known to be associated with schizophrenia.

  19. Switchable circular beam deflectors

    NASA Astrophysics Data System (ADS)

    Shang, Xiaobing; Joshi, Pankaj; Tan, Jin-Yi; De Smet, Jelle; Cuypers, Dieter; Baghdasaryan, Tigran; Vervaeke, Michael; Thienpont, Hugo; De Smet, Herbert

    2016-04-01

    In this work, we report two types of electrically tunable photonic devices with circularly symmetric polarization independent beam steering performance (beam condensing resp. beam broadening). The devices consist of circular micro grating structures combined with nematic liquid crystal (LC) layers with anti-parallel alignment. A single beam deflector converts a polarized and monochromatic green laser beam (λ =543.5 nm) into a diffraction pattern, with the peak intensity appearing at the third order when 0~{{V}\\text{pp}} is applied and at the zeroth order (no deflection) for voltages above 30~{{V}\\text{pp}} . Depending on the shape of the grating structure (non-inverted or inverted), the deflection is inwards or outwards. Both grating types can be made starting from the same diamond-tooled master mold. A polarized white light beam is symmetrically condensed resp. broadened over 2° in the off state and is passed through unchanged in the on state. By stacking two such devices with mutually orthogonal LC alignment layers, polarization independent switchable circular beam deflectors are realized with a high transmittance (>80%), and with the same beam steering performance as the polarization dependent single devices.

  20. A sensitive magnetic nanoparticle-based immunoassay of phosphorylated acetylcholinesterase using protein cage templated lead phosphate for signal amplification with graphite furnace atomic absorption spectrometry detection.

    PubMed

    Liang, Pei; Kang, Caiyan; Yang, Enjian; Ge, Xiaoxiao; Du, Dan; Lin, Yuehe

    2016-04-01

    We developed a new magnetic nanoparticle sandwich-like immunoassay using protein cage nanoparticles (PCN) for signal amplification together with graphite furnace atomic absorption spectrometry (GFAAS) for the quantification of an organophosphorylated acetylcholinesterase adduct (OP-AChE), the biomarker of exposure to organophosphate pesticides (OPs) and nerve agents. OP-AChE adducts were firstly captured by titanium dioxide coated magnetic nanoparticles (TiO2-MNPs) from the sample matrixes through metal chelation with phospho-moieties, and then selectively recognized by anti-AChE antibody labeled on PCN which was packed with lead phosphate in its cavity (PCN-anti-AChE). The sandwich-like immunoreaction was performed among TiO2-MNPs, OP-AChE and PCN-anti-AChE to form a TiO2-MNP/OP-AChE/PCN-anti-AChE immunocomplex. The complex could be easily isolated from the sample solution with the help of magnet, and the released lead ions from PCN were detected by GFAAS for the quantification of OP-AChE. Greatly enhanced sensitivity was achieved because PCN increased the amount of metal ions in the cavity of each apoferritin. The proposed immunoassay yielded a linear response over a broad range of OP-AChE concentrations from 0.01 nM to 2 nM, with a detection limit of 2 pM, which has enough sensitivity for monitoring of low-dose exposure to OPs. This new method showed an acceptable stability and reproducibility and was validated with OP-AChE spiked human plasma.

  1. Sensitive magnetic nanoparticle-based immunoassay of phosphorylated acetylcholinesterase using protein cage templated lead phosphate for signal amplification with graphite furnace atomic absorption spectrometry detection

    PubMed Central

    Liang, Pei; Kang, Caiyan; Yang, Enjian; Ge, Xiaoxiao; Du, Dan; Lin, Yuehe

    2016-01-01

    We developed a new magnetic nanoparticles sandwich-like immunoassay using protein cage nanoparticles (PCN) for signal amplification together with graphite furnace atomic absorption spectrometry (GFAAS) for quantification of organophosphorylated acetylcholinesterase adduct (OP-AChE), the biomarker of exposure to organophosphate pesticides (OPs) and nerve agents. OP-AChE adducts were firstly captured by titanium dioxide coated magnetic nanoparticles (TiO2-MNPs) from the sample matrixes through metal chelation with phospho-moieties, and then selectively recognized by anti-AChE antibody labeled on PCN which was packed with lead phosphate in its cavity (PCN-anti-AChE). The sandwich-like immunoreaction was performed among TiO2-MNPs, OP-AChE and PCN-anti-AChE to form TiO2-MNPs/OP-AChE/PCN-anti-AChE immunocomplex. The complex could be easily isolated from the sample solution with the help of magnet, and the released lead ions from PCN were detected by GFAAS for the quantification of OP-AChE. Greatly enhanced sensitivity was achieved because PCN increased the amount of metal ions in the cavity of each apoferritin. The proposed immunoassay yielded a linear response over a broad OP-AChE concentrations from 0.01 nM to 2 nM, with a detection limit of 2 pM, which has enough sensitivity for monitoring of low-dose exposure to OPs. This new method showed an acceptable stability and reproducibility and was validated with OP-AChE spiked human plasma. PMID:26953358

  2. A sensitive magnetic nanoparticle-based immunoassay of phosphorylated acetylcholinesterase using protein cage templated lead phosphate for signal amplification with graphite furnace atomic absorption spectrometry detection.

    PubMed

    Liang, Pei; Kang, Caiyan; Yang, Enjian; Ge, Xiaoxiao; Du, Dan; Lin, Yuehe

    2016-04-01

    We developed a new magnetic nanoparticle sandwich-like immunoassay using protein cage nanoparticles (PCN) for signal amplification together with graphite furnace atomic absorption spectrometry (GFAAS) for the quantification of an organophosphorylated acetylcholinesterase adduct (OP-AChE), the biomarker of exposure to organophosphate pesticides (OPs) and nerve agents. OP-AChE adducts were firstly captured by titanium dioxide coated magnetic nanoparticles (TiO2-MNPs) from the sample matrixes through metal chelation with phospho-moieties, and then selectively recognized by anti-AChE antibody labeled on PCN which was packed with lead phosphate in its cavity (PCN-anti-AChE). The sandwich-like immunoreaction was performed among TiO2-MNPs, OP-AChE and PCN-anti-AChE to form a TiO2-MNP/OP-AChE/PCN-anti-AChE immunocomplex. The complex could be easily isolated from the sample solution with the help of magnet, and the released lead ions from PCN were detected by GFAAS for the quantification of OP-AChE. Greatly enhanced sensitivity was achieved because PCN increased the amount of metal ions in the cavity of each apoferritin. The proposed immunoassay yielded a linear response over a broad range of OP-AChE concentrations from 0.01 nM to 2 nM, with a detection limit of 2 pM, which has enough sensitivity for monitoring of low-dose exposure to OPs. This new method showed an acceptable stability and reproducibility and was validated with OP-AChE spiked human plasma. PMID:26953358

  3. In situ emulsification microextraction using a dicationic ionic liquid followed by magnetic assisted physisorption for determination of lead prior to micro-sampling flame atomic absorption spectrometry.

    PubMed

    Shokri, Masood; Beiraghi, Asadollah; Seidi, Shahram

    2015-08-19

    For the first time, a simple and efficient in situ emulsification microextraction method using a dicationic ionic liquid followed by magnetic assisted physisorption was presented to determine trace amounts of lead. In this method, 400 μL of 1.0 mol L(-1) lithium bis (trifluoromethylsulfonyl) imide aqueous solution, Li[NTf2], was added into the sample solution containing 100 μL of 1.0 mol L(-1) 1,3-(propyl-1,3-diyl) bis (3-methylimidazolium) chloride, [pbmim]Cl2, to form a water immiscible ionic liquid, [pbmim][NTf2]2. This new in situ formed dicationic ionic liquid was applied as the acceptor phase to extract the lead-ammonium pyrrolidinedithiocarbamate (Pb-APDC) complexes from the sample solution. Subsequently, 30 mg of Fe3O4 magnetic nanoparticles (MNPs) were added into the sample solution to collect the fine droplets of [pbmim][NTf2]2, physisorptively. Finally, MNPs were eluted by acetonitrile, separated by an external magnetic field and the obtained eluent was subjected to micro-sampling flame atomic absorption spectrometry (FAAS) for further analysis. Comparing with other microextraction methods, no special devices and centrifugation step are required. Parameters influencing the extraction efficiency such as extraction time, pH, concentration of chelating agent, amount of MNPs and coexisting interferences were studied. Under the optimized conditions, this method showed high extraction recovery of 93% with low LOD of 0.7 μg L(-1). Good linearity was obtained in the range of 2.5-150 μg L(-1) with determination coefficient (r(2)) of 0.9921. Relative standard deviation (RSD%) for seven repeated measurements at the concentration of 10 μg L(-1) was 4.1%. Finally, this method was successfully applied for determination of lead in some water and plant samples. PMID:26343434

  4. GC base sequence recognition by oligo(imidazolecarboxamide) and C-terminus-modified analogues of distamycin deduced from circular dichroism, proton nuclear magnetic resonance, and methidiumpropylethylenediaminetetraacetate-iron(II) footprinting studies.

    PubMed

    Lee, M; Rhodes, A L; Wyatt, M D; Forrow, S; Hartley, J A

    1993-04-27

    The DNA binding properties of a series of imidazole-containing and C-terminus-modified analogues 4-7 of distamycin are described. These analogues contain one to four imidazole units, respectively. Data from the ethidium displacement assay showed that these compounds bind in the minor groove of DNA, with the relative order of binding constants of 6 (Im3) > 7 (Im4) > 5 (Im2) > 4 (Im1). The reduced binding constants of these compounds for poly(dA-dT) relative to distamycin, while they still interact strongly with poly(dG-dC), provided evidence of GC sequence acceptance. The preferences for GC-rich sequences by these compounds were established from a combination of circular dichroism (CD) titration, proton nuclear magnetic resonance (1H-NMR), and methidiumpropylethylenediaminetetraacetate-iron(II) [MPE.Fe-(II)] footprinting studies. In the CD studies, these compounds produced significantly larger DNA-induced ligand bands with poly(dG-dC) than poly(dA-dT) at comparable ligand concentrations. 1H-NMR studies of the binding of 5 to d-[CATGGCCATG]2 provided further evidence of the recognition of GC sequences by these compounds, and suggested that the ligand was located on the underlined sequence in the minor groove with the C-terminus oriented over the T residue. MPE footprinting studies on a GC-rich BamHI/SalI fragment of pBR322 provided unambiguous evidence for the GC sequence selectivity for some of these compounds. Compounds 4 and 7 produced poor footprints on the gels; however, analogues 5 and 6 gave strong footprints.(ABSTRACT TRUNCATED AT 250 WORDS)

  5. SIMULTANEOUS MEASUREMENT OF CIRCULAR DICHROISM AND FLUORESCENCE POLARIZATION ANISOTROPY.

    SciTech Connect

    SUTHERLAND,J.C.

    2002-01-19

    Circular dichroism and fluorescence polarization anisotropy are important tools for characterizing biomolecular systems. Both are used extensively in kinetic experiments involving stopped- or continuous flow systems as well as titrations and steady-state spectroscopy. This paper presents the theory for determining circular dichroism and fluorescence polarization anisotropy simultaneously, thus insuring the two parameters are recorded under exactly the same conditions and at exactly the same time in kinetic experiments. The approach to measuring circular dichroism is that used in almost all conventional dichrographs. Two arrangements for measuring fluorescence polarization anisotropy are described. One uses a single fluorescence detector and signal processing with a lock-in amplifier that is similar to the measurement of circular dichroism. The second approach uses classic ''T'' format detection optics, and thus can be used with conventional photon-counting detection electronics. Simple extensions permit the simultaneous measurement of the absorption and excitation intensity corrected fluorescence intensity.

  6. 1D magnetic materials of Fe₃O₄ and Fe with high performance of microwave absorption fabricated by electrospinning method.

    PubMed

    Han, Rui; Li, Wei; Pan, Weiwei; Zhu, Minggang; Zhou, Dong; Li, Fa-shen

    2014-01-01

    Fe3O4 and Fe nanowires are successfully fabricated by electrospinning method and reduction process. Wiry microstructures were achieved with the phase transformation from α-Fe2O3 to Fe3O4 and Fe by partial and full reduction, while still preserving the wire morphology. The diameters of the Fe3O4 and Fe nanowires are approximately 50-60 nm and 30-40 nm, respectively. The investigation of microwave absorption reveals that the Fe3O4 nanowires exhibit excellent microwave absorbing properties. For paraffin-based composite containing 50% weight concentration of Fe3O4 nanowires, the minimum reflection loss reaches -17.2 dB at 6.2 GHz with the matching thickness of 5.5 mm. Furthermore, the calculation shows that the modulus of the ratio between the complex permittivity and permeability |ε/μ| is far away from unity at the minimum reflection loss point, which is quite different from the traditional opinions. PMID:25510415

  7. Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy.

    PubMed

    Ueno, Tetsuro; Sinha, Jaivardhan; Inami, Nobuhito; Takeichi, Yasuo; Mitani, Seiji; Ono, Kanta; Hayashi, Masamitsu

    2015-01-01

    We have studied the magnetic layer thickness dependence of the orbital magnetic moment in magnetic heterostructures to identify contributions from interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlOx and Pt/Co/Pt, which possess significant interface contribution to the perpendicular magnetic anisotropy, are studied as model systems. X-ray magnetic circular dichroism spectroscopy is used to evaluate the relative orbital moment, i.e. the ratio of the orbital to spin moments, of the magnetic elements constituting the heterostructures. We find that the relative orbital moment of Co in Pt/Co/Pt remains constant against its thickness whereas the moment increases with decreasing Co layer thickness for Pt/Co/AlOx, suggesting that a non-zero interface orbital moment exists for the latter system. For Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray absorption spectra shows that a particular oxidized Co state in Pt/Co/AlOx, absent in other heterosturctures, may give rise to the interface orbital moment in this system. These results show element specific contributions to the interface orbital magnetic moments in ultrathin magnetic heterostructures. PMID:26456454

  8. Rectenna composed of a circular microstrip antenna

    SciTech Connect

    Itoh, K.; Ohgane, T.; Ogawa, Y.

    1986-01-01

    One of the big problems in the SPS system is reradiation of the harmonic waves generated by the rectifying diode. The authors proposed the use of a circular microstrip antenna (CMSA), since the CMSA has no higher resonance-harmonic of integer multiple of the dominant resonance frequency. However, characteristics of a large rectenna array of CMSA's have not been clarified. This paper is concerned with the absorption efficiency of the rectenna composed of the CMSA. The efficiency is estimated explicitly using an infinite array model. The results show that the absorption efficiency of the infinite rectenna array composed of the CMSA is 100%. Also, this paper considers the effect of the losses of the composed of the CMSA is 100%. Also, this paper considers the effect of the losses of the CMSA. 4 references, 4 figures.

  9. Planetary Rings: Circular and Non-circular

    NASA Astrophysics Data System (ADS)

    French, R. G.; Nicholson, P. D.; Colwell, J.; Marouf, E. A.; Rappaport, N. J.; Hedman, M. M.; McGhee, C.; Lonergan, K.; Sepersky, T.

    2011-12-01

    Although Saturn's rings appear at first glance to be axisymmetric, more precise measurements reveal that many of the gap edges and narrow ringlets within the rings are noncircular, a characteristic they share with the narrow uranian rings. A careful study of these features is of interest for several reasons: (i) resonantly-forced perturbations are believed to prevent the rings from spreading under the influence of collisions, (ii) unforced distortions, mostly eccentricities, can lead to estimates of the surface mass density and viscosity of the rings, and (iii) accurately-measured apsidal precession rates provide information on Saturn's zonal gravity harmonics. We present preliminary results from a comprehensive study of noncircular features in the Cassini Division and in the C ring. The data used in this study come from three Cassini experiments, and cover the period from May 2005 to September 2010. Over 120 stellar occultations have been observed by the Ultraviolet Imaging Spectrometer (UVIS) and by the Visual and Infrared Imaging Spectrometer (VIMS). In addition, we include 12 occultations of the spacecraft's radio Radio Science Subsystem (RSS) by the rings observed on Earth in May-September 2005. The simplest noncircular features can be modeled as inclined Keplerian ellipses, freely precessing under the influence of Saturn's oblate gravity field. In agreement with similar fits to the VIMS occultation data alone, we find that the inner edges of 7 of the 8 gaps within the Cassini Division are eccentric, with amplitudes ranging from 0.9 km to 28.3 km. In contrast, most of the outer gap edges are near-circular. We also find a rich assortment of normal modes on the edges of both ringlets and gaps. We have searched for modes with wavenumber m as high as 8, and find convincing evidence for modes with m = 0, 2, 3, 4 and 5, all with amplitudes of 1 km or greater. In some cases, as many as 3 or 4 normal modes coexist at a single edge with comparable amplitudes. Our fits

  10. Two novel POM-based inorganic-organic hybrid compounds: synthesis, structures, magnetic properties, photodegradation and selective absorption of organic dyes.

    PubMed

    Dui, Xue-Jing; Yang, Wen-Bin; Wu, Xiao-Yuan; Kuang, Xiaofei; Liao, Jian-Zhen; Yu, Rongmin; Lu, Can-Zhong

    2015-05-28

    The hydrothermal reactions of a mixture of (NH4)6Mo7O24·4H2O, Cu(Ac)2·H2O and 3-bpo ligands at different temperatures result in the isolation of two novel inorganic-organic hybrid materials containing different but related isopolymolybdate units, [Cu(3-bpo)(H2O)(Mo4O13)]·3H2O () and [Cu2(3-bpo)2(Mo6O20)] (). The {Mo4O13}n chains in and unprecedented [Mo6O20](4-) isopolyhexamolybdate anions in are linked by octahedral Cu(2+) ions into two-dimensional hybrid layers. Interestingly, 3-bpo ligands in both and are located on either side of these hybrid layers and serve as arched footbridges to link Cu(ii) ions in the layer via pyridyl N-donors, and at the same time connect these hybrid layers into 3D supramolecular frameworks via weak MoNoxadiazole bonds. Another important point for is that water clusters are filled in the 1D channels surrounded by isopolytetramolybdate units. In addition, dye adsorption and photocatalytic properties of and magnetic properties of have been investigated. The results indicated that complex is not only a good heterogeneous photocatalyst in the degradation of methyl orange (MO) and methylene blue (MB), but also has high absorption capacity of MB at room temperature and can selectively capture MB molecules from binary mixtures of MB/MO or MB/RhB. All MB molecules absorbed on can be completely released and photodegraded in the presence of adequate peroxide. The temperature dependence of magnetic susceptibility revealed that complex exhibits antiferromagnetic ordering at about 5 K, and a spin-flop transition was observed at about 5.8 T at 2 K, indicating metamagnetic-like behaviour from antiferromagnetic to ferromagnetic phases.

  11. Magnetic solid-phase extraction combined with graphite furnace atomic absorption spectrometry for speciation of Cr(III) and Cr(VI) in environmental waters.

    PubMed

    Jiang, Hong-mei; Yang, Ting; Wang, Yan-hong; Lian, Hong-zhen; Hu, Xin

    2013-11-15

    A new approach of magnetic solid phase extraction (MSPE) coupled with graphite furnace atomic absorption spectrometry (GFAAS) has been developed for the speciation of Cr(III) and Cr(VI) using zincon-immobilized silica-coated magnetic Fe3O4 nanoparticles (Zincon-Si-MNPs) as the MSPE absorbent. Cr(III) was quantitatively reserved on the absorbent at pH 9.1 while total Cr was reserved at pH 6.5. The absorbed Cr species were eluted by using 2 mol/L HCl and detected by GFAAS. The concentration of Cr(VI) could be calculated by subtracting Cr(III) from total Cr. All the parameters affecting the separation and extraction efficiency of Cr species such as pH, extraction time, concentration and volume of eluent, sample volume and influence of co-existing ions were systematically examined and the optimized conditions were established accordingly. The detection limit (LOD) of the method was 0.016 and 0.011 ng mL(-1) for Cr(III) and Cr(VI), respectively, with the enrichment factor of 100 and 150. The precisions of this method (Relative standard deviation, RSD, n=7) for Cr(III) and Cr(VI) at 0.1 ng mL(-1) were 6.0% and 6.2%, respectively. In order to validate the proposed method, a certified reference material of environmental water was analyzed, and the result of Cr speciation was in good agreement with the certified value. This MSPE-GFAAS method has been successfully applied for the speciation of Cr(III) and Cr(VI) in lake and tap waters with the recoveries of 88-109% for the spiked samples. Moreover, the MSPE separation mechanism of Cr(III) and Cr(VI) based on their adsorption-desorption on Zincon-Si-MNPs has been explained through various spectroscopic characterization.

  12. Driven dynamic mode-splitting of the magnetic vortex translational resonance.

    SciTech Connect

    Buchanan, K. S.; Grimsditch, M.; Fradin, F. Y.; Bader, S. D.; Novosad, V.

    2007-12-31

    A magnetic vortex in a restricted geometry possesses a nondegenerate translational excitation that corresponds to circular motion of its core at a characteristic frequency. For 40-nm thick, micron-sized permalloy elements, we find that the translational-mode microwave absorption peak splits into two peaks that differ in frequency by up to 25% as the driving field is increased. An analysis of micromagnetic equations shows that for large driving fields two stable solutions emerge.

  13. X-ray induced demagnetization of single-molecule magnets

    SciTech Connect

    Dreiser, Jan; Westerström, Rasmus; Piamonteze, Cinthia; Nolting, Frithjof; Rusponi, Stefano; Brune, Harald; Yang, Shangfeng; Popov, Alexey; Dunsch, Lothar; Greber, Thomas

    2014-07-21

    Low-temperature x-ray magnetic circular dichroism measurements on the endohedral single-molecule magnet DySc{sub 2}N@C{sub 80} at the Dy M{sub 4,5} edges reveal a shrinking of the opening of the observed hysteresis with increasing x-ray flux. Time-dependent measurements show that the exposure of the molecules to x-rays resonant with the Dy M{sub 5} edge accelerates the relaxation of magnetization more than off-resonant x-rays. The results cannot be explained by a homogeneous temperature rise due to x-ray absorption. Moreover, the observed large demagnetization cross sections indicate that the resonant absorption of one x-ray photon induces the demagnetization of many molecules.

  14. Circularly polarized conical patterns from circular microstrip antennas

    NASA Technical Reports Server (NTRS)

    Huang, J.

    1984-01-01

    A method is presented for generating circularly polarized conical patterns from circular microstrip antennas. These antennas are excited at higher order modes and require different feed arrangements for different mode excitations. It is determined that the peak direction of the conical pattern can be varied over a wide angular range. Modal expansion technique is employed to calculate the radiation patterns of these antennas.

  15. Circularly polarized microstrip antennas

    NASA Technical Reports Server (NTRS)

    Lo, Y. T.; Engst, B.; Lee, R. Q. H.

    1985-01-01

    A simple microstrip antenna can be made to radiate EM waves of any polarization, in particular, the circular polarization (CP) without any phasing network and power divider. A simple and accurate theory for this family of antennas was developed. However, the CP bandwidth, (CPBW) the bandwidth in which the axial ratio (AR) is less than a certain specified value, is very small. Most of the experimental designs were made for a feed placed along the diagonal of the patch. It is shown that there are practically infinitely many possible designs with different feed location. The speculation that other designs might give a wider bandwidth is clarified and an effective method for broadening the bandwidth is shown.

  16. CIRCULAR CAVITY SLOT ANTENNA

    DOEpatents

    Kerley, P.L.

    1959-01-01

    A small-size antenna having a doughnut-shaped field pattern and which can act both as an antenna and a resonant circuit is described. The antenna is of the slotted type and comprises a resonant cavity with a center hole. A circular slot is provided in one wall of the cavity concentric with the hole and a radio frequency source is connected across the slot. The pattern and loading of the antenna are adjusted by varying the position and shape of a center element slidably disposed within the hole and projecting from the slotted side of the resonant cavity. The disclosed structure may also be used to propagate the oscillator signal down a transniission line by replacing the center element with one leg of the transmission line in a spaced relation from the walls of the cavity.

  17. Circularly Polarized MHOHG with Bichromatic Circularly Polarized Laser Pulses

    NASA Astrophysics Data System (ADS)

    Bandrauk, Andre D.; Mauger, Francois; Uzer, Turgay

    2016-05-01

    Circularly polarized MHOHG-Molecular High Order Harmonic Generation is shown to occur efficiently with intense ultrashort bichromatic circularly polarized pulses due to frequent electron-parent -ion recollision with co-or counter-rotating incident circular pulses as predicted in 1995. We show in this context that molecules offer a very robust and efficient frameworkfor the production of circularly polarized harmonics for the generation of single circularly polarized ``attosecond'' pulses. The efficiency of such new MHOHG is shown to depend on the compatibility of the symmetry of the molecular medium with the net electric field generated by the combination of the laser pulses.Using a time-dependent symmetry analysis with concrete examples such as H 2 + vs H 3 + we show how all the features(harmonic order and ∧ polarization) of MHOHG can be explained and predicted.

  18. Characterization and remote sensing of biological particles using circular polarization

    NASA Astrophysics Data System (ADS)

    Nagdimunov, Lev; Kolokolova, Ludmilla; Mackowski, Daniel

    2013-12-01

    Biological molecules are characterized by an intrinsic asymmetry known as homochirality. The result is optical activity of biological materials and circular polarization in the light scattered by microorganisms, cells of living organisms, as well as molecules (e.g. amino acids) of biological origin. Lab measurements (Sparks et al. (2009) [6,7]) have found that light scattered by certain biological systems, in particular photosynthetic organisms, is not only circular polarized but contains a characteristic spectral trend, showing a fast change and reversal of sign for circular polarization within absorption bands. Similar behavior can be expected for other biological and prebiological organics, especially amino acids. We begin our study by reproducing the laboratory measurements for photosynthetic organisms through modeling the biological material as aggregated structures and using the Multiple Sphere T-matrix (MSTM) code for light scattering calculations. We further study how the spectral effect described above depends on the porosity of the aggregates and the size and number of the constituent particles (monomers). We show that larger aggregates are characterized by larger values of circular polarization and discuss how light-scattering characteristics of individual monomers and electromagnetic interaction between them affect this result. We find that circular polarization typically peaks at medium (40-140°) scattering angles, and discuss recommendations for efficient remote observation of circular polarization from (pre)biological systems.

  19. Circular extinction of plasmonic silver nanocaps and gas sensing.

    PubMed

    Li, Jun; Kotov, Nicholas A

    2016-01-01

    Chiral plasmonic nanostructures exhibit strong rotatory optical activity and are expected to enrich the field of metaoptical materials. Potential applications of chiroplasmonic nanostructures include circular polarizers, optical polarization detectors, asymmetric catalysts, and sensors. However, chiral plasmonic materials require subwavelength structural control and involve laborious chemical or lithographic procedures for their manufacturing. Moreover, strong rotatory activity of subwavelength structures whose chirality was imparted by microfabrication, has been obtained for the red and infrared parts of the spectrum but faces new challenges for the blue and violet spectral ranges even with plasmonic materials with plasmonic bands in the 200-400 nm window. In this study, we address this problem by preparing chiral subwavelength nanostructures by glancing angle sputtering of metallic silver on ZnO nanopillar arrays. Silver deposition in two different planes is a convenient method for preparation of silver chiroplasmonic nanocaps (Ag CPNCs) with controlled asymmetry. Circular dichroism spectroscopy was used to examine the circular extinction for the left-handed nanocaps (L-CPNCs) with understanding that not only circular dichroism but also many other optical effects contribute to the amplitude of these bands. The pillared silver films exhibit circular extinction in the violet area of the electromagnetic spectrum. Partial oxidation of Ag to AgxO causes the absorption and corresponding circular extinction band obtained using a conventional CD spectrometer at 400-525 nm to increase and shift. This optical material may be used to detect oxygen and extends the spectrum of application of chiroplasmonic materials to gas sensing. PMID:26952921

  20. Preliminary assessment of dispersion versus absorption analysis of high spectral and spatial resolution magnetic resonance images in the diagnosis of breast cancer

    PubMed Central

    Weiss, William A.; Medved, Milica; Karczmar, Gregory S.; Giger, Maryellen L.

    2015-01-01

    Abstract. Water resonance lineshapes observed in breast lesions imaged with high spectral and spatial resolution (HiSS) magnetic resonance imaging have been shown to contain diagnostically useful non-Lorentzian components. The purpose of this work is to update a previous method of breast lesion diagnosis by including phase-corrected absorption and dispersion spectra. This update includes information about the shape of the complex water resonance, which could improve the performance of a computer-aided diagnosis breast lesion classification scheme. The non-Lorentzian characteristics observed in complex breast lesion water resonance spectra are characterized by comparing a plot of the real versus imaginary components of the spectrum to that of a perfect complex Lorentzian spectrum, a “dispersion versus absorption” (DISPA) analysis technique. Distortion in the shape of the observed spectra indicates underlying physiologic changes, which have been shown to be correlated with malignancy. These spectral shape distortions in each lesion voxel are quantified by summing the deviations in DISPA radius from an ideal complex Lorentzian spectrum over all Fourier components, yielding a “total radial difference” (TRD). We limited our analysis to those voxels in each lesion with the largest TRD. The number of voxels considered was dependent on the lesion size. The TRD was used to classify voxels from 15 malignant and 8 benign lesions (∼2400 voxels after voxel elimination). Lesion discrimination performance was evaluated for both the average and variance of the TRD within each lesion. Area under the receiver operating characteristic curve (ROC AUC) was used to assess both the voxel- and lesion-based discrimination methods in the task of distinguishing between malignant and benign. In the task of distinguishing voxels from malignant and benign lesions, TRD yielded an AUC of 0.89 (95% confidence interval [0.84, 0.91]). In the task of distinguishing malignant from benign

  1. Circular chemiresistors for microchemical sensors

    DOEpatents

    Ho, Clifford K.

    2007-03-13

    A circular chemiresistor for use in microchemical sensors. A pair of electrodes is fabricated on an electrically insulating substrate. The pattern of electrodes is arranged in a circle-filling geometry, such as a concentric, dual-track spiral design, or a circular interdigitated design. A drop of a chemically sensitive polymer (i.e., chemiresistive ink) is deposited on the insulating substrate on the electrodes, which spreads out into a thin, circular disk contacting the pair of electrodes. This circularly-shaped electrode geometry maximizes the contact area between the pair of electrodes and the polymer deposit, which provides a lower and more stable baseline resistance than with linear-trace designs. The circularly-shaped electrode pattern also serves to minimize batch-to-batch variations in the baseline resistance due to non-uniform distributions of conductive particles in the chemiresistive polymer film.

  2. 76 FR 62148 - Title VI; Proposed Circular, Environmental Justice; Proposed Circular

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-06

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  3. Measuring brain manganese and iron accumulation in rats following 14 weeks of low-dose manganese treatment using atomic absorption spectroscopy and magnetic resonance imaging.

    PubMed

    Fitsanakis, Vanessa A; Zhang, Na; Anderson, Joel G; Erikson, Keith M; Avison, Malcolm J; Gore, John C; Aschner, Michael

    2008-05-01

    Chronic exposure to manganese (Mn) may lead to a movement disorder due to preferential Mn accumulation in the globus pallidus and other basal ganglia nuclei. Iron (Fe) deficiency also results in increased brain Mn levels, as well as dysregulation of other trace metals. The relationship between Mn and Fe transport has been attributed to the fact that both metals can be transported via the same molecular mechanisms. It is not known, however, whether brain Mn distribution patterns due to increased Mn exposure vs. Fe deficiency are the same, or whether Fe supplementation would reverse or inhibit Mn deposition. To address these questions, we utilized four distinct experimental populations. Three separate groups of male Sprague-Dawley rats on different diets (control diet [MnT], Fe deficient [FeD], or Fe supplemented [FeS]) were given weekly intravenous Mn injections (3 mg Mn/kg body mass) for 14 weeks, whereas control (CN) rats were fed the control diet and received sterile saline injections. At the conclusion of the study, both blood and brain Mn and Fe levels were determined by atomic absorption spectroscopy and magnetic resonance imaging. The data indicate that changes in dietary Fe levels (either increased or decreased) result in regionally specific increases in brain Mn levels compared with CN or MnT animals. Furthermore, there was no difference in either Fe or Mn accumulation between FeS or FeD animals. These data suggest that dietary Fe manipulation, whether increased or decreased, may contribute to brain Mn deposition in populations vulnerable to increased Mn exposure.

  4. Circular paraboloid reflection cell for laser spectroscopic trace gas analysis.

    PubMed

    Mangold, Markus; Tuzson, Béla; Hundt, Morten; Jágerská, Jana; Looser, Herbert; Emmenegger, Lukas

    2016-05-01

    Absorption cells with circular geometry are a class of multipass reflection cells consisting of a single, circular mirror. They can be particularly favorable for trace gas measurements because of their mechanical robustness, simplicity, and their optical versatility. In this article, we present detailed theoretical considerations and ray tracing simulations for the optimization of the optical design of circular multipass reflection cells. A parabolic mirror shape in a confocal arrangement is found to be most suitable for long optical paths in a small volume. We experimentally demonstrate more than 12 m optical path in a 14.5 cm diameter gas cell and NO2 concentration measurements in ambient air with a measurement precision better than 0.1 ppb. PMID:27140888

  5. Circular dichroism in magnesium sulfite hexahydrate doped with cobalt

    NASA Astrophysics Data System (ADS)

    Bunzarov, Zh.; Iliev, I.; Dimov, T.; Petkova, P.; Kovachev, Tz.; Lyutov, L.; Tzoukrovski, Y.

    2009-10-01

    The new nonlinear crystal of magnesium sulfite hexahydrate (MgSO3.6H2O) belongs to the rare crystallographic class C3 (without a symmetry centre), the other known only representative being sodium periodate (NaIO4). There are some scarce data in the scientific papers about magnesium sulfite hexahydrate's physical properties. Single crystals of significant sizes (up to 40-50 mm) of MgSO3.6H2O as well as such, doped with Ni, Co, and Zn, for the time being are grown only by our own method developed in the Laboratory for Crystal growth at the Faculty of Physics of Sofia University. Recently we have observed the supposed presence of optical activity. Circular dichroism is not observed in pure MgSO3.6H2O. The results of the first ever investigations are presented, which demonstrate the presence of circular dichroism in MgSO3.6H2O doped with Co. The circular dichroism appears in the spectral range from 420 nm to 580 nm. The spectrum of circular dichroism demonstrates a well expressed structure - an isolated maximum at 470 nm and a combination of two overlapped maxima at ~ 495 nm and 520 nm respectively. The spectrum of the circular dichroism is compared with the absorption spectrum of MgSO3.6H2O:Co, along the direction (0001) and with the linear dichroism spectrum measured in direction(1210). It is shown in this way that the circular dichroism appears only in the spectral range of the optical absorption structure due to Co dopant. In the same spectral range can be observed also the linear dichroism determined by Co presence in MgSO3.6H2O.

  6. Ab Initio Theory of Coherent Laser-Induced Magnetization in Metals

    NASA Astrophysics Data System (ADS)

    Berritta, Marco; Mondal, Ritwik; Carva, Karel; Oppeneer, Peter M.

    2016-09-01

    We present the first materials specific ab initio theory of the magnetization induced by circularly polarized laser light in metals. Our calculations are based on nonlinear density matrix theory and include the effect of absorption. We show that the induced magnetization, commonly referred to as inverse Faraday effect, is strongly materials and frequency dependent, and demonstrate the existence of both spin and orbital induced magnetizations which exhibit a surprisingly different behavior. We show that for nonmagnetic metals (such as Cu, Au, Pd, Pt) and antiferromagnetic metals the induced magnetization is antisymmetric in the light's helicity, whereas for ferromagnetic metals (Fe, Co, Ni, FePt) the imparted magnetization is only asymmetric in the helicity. We compute effective optomagnetic fields that correspond to the induced magnetizations and provide guidelines for achieving all-optical helicity-dependent switching.

  7. Linear and circular spectropolarimetry of diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Cox, N. L. J.; Ehrenfreund, P.; Foing, B. H.; D'Hendecourt, L.; Salama, F.; Sarre, P. J.

    2011-07-01

    Context. The identification of the carriers of diffuse interstellar bands (DIBs) remains one of the long-standing mysteries in astronomy. The detection of a polarisation signal in a DIB profile can be used to distinguish between a dust or gas-phase carrier. The polarisation profile can give additional information on the grain or molecular properties of the absorber. Aims: To measure the polarisation efficiency of the carriers of the diffuse interstellar bands. Methods: In order to detect and measure the linear and circular polarisation of the DIBs we observed reddened lines of sight showing continuum polarisation. For this study we selected two stars HD 197770 and HD 194279. We used high-resolution (R ~ 64 000) spectropolarimetry in the wavelength range from 3700 to 10 480 Å with the ESPaDOnS échelle spectrograph mounted at the CFHT. Results: High S/N and high resolution Stokes V (circular), Q and U (linear) spectra were obtained. We constrained upper limits by a factor of 10 for previously observed DIBs. Furthermore, we analysed ~30 additional DIBs for which no spectropolarimetry data has been obtained before. This included the 9577 Å DIB and the 8621 Å DIB. The former is attributed to the C60^+ fullerene, which could become aligned in a magnetic field. The latter shows a tight correlation with the amount of dust in the line-of-sight and therefore most likely may show a polarisation signal related the aligned grains. Conclusions: The lack of polarisation in 45 DIB profiles suggests that none of the absorption lines is induced by a grain-type carrier. The strict upper limits, less than ~0.01%, derived for the observed lines-of-sight imply that if DIBs are due to gas-phase molecules these carriers have polarisation efficiencies which are at least 6 times, and up to 300 times, smaller than those predicted for grain-related carriers. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of

  8. Beam Rounders for Circular Colliders

    SciTech Connect

    A. Burov; S. Nagaitsev; Ya. Derbenev

    2001-07-01

    By means of linear optics, an arbitrary uncoupled beam can be locally transformed into a round (rotation-invariant) state and then back. This provides an efficient way to round beams in the interaction region of circular colliders.

  9. Biological Synthesis of Circular Polypeptides*

    PubMed Central

    Aboye, Teshome L.; Camarero, Julio A.

    2012-01-01

    Here, we review the use of different biochemical approaches for biological synthesis of circular or backbone-cyclized proteins and peptides. These methods allow the production of circular polypeptides either in vitro or in vivo using standard recombinant DNA expression techniques. Protein circularization can significantly impact protein engineering and research in protein folding. Basic polymer theory predicts that circularization should lead to a net thermodynamic stabilization of a folded protein by reducing the entropy associated with the unfolded state. Protein cyclization also provides a valuable tool for exploring the effects of topology on protein folding kinetics. Furthermore, the biological production of cyclic polypeptides makes possible the production of cyclic polypeptide libraries. The generation of such libraries, which was previously restricted to the domain of synthetic chemists, now offers biologists access to highly diverse and stable molecular libraries for probing protein structure and function. PMID:22707722

  10. Circularly-Polarized Microstrip Antenna

    NASA Technical Reports Server (NTRS)

    Stanton, P. H.

    1985-01-01

    Microstrip construction compact for mobile applications. Circularly polarized microstrip antenna made of concentric cylindrical layers of conductive and dielectric materials. Coaxial cable feedlines connected to horizontal and vertical subelements from inside. Vertical subelement acts as ground for horizontal subelement.

  11. Beam rounders for circular colliders

    SciTech Connect

    A. Burov and S. Nagaitsev

    2002-12-10

    By means of linear optics, an arbitrary uncoupled beam can be locally transformed into a round (rotation-invariant) state and then back. This provides an efficient way to round beams in the interaction region of circular colliders.

  12. Quantum-cascade laser-based vibrational circular dichroism.

    PubMed

    Lüdeke, Steffen; Pfeifer, Marcel; Fischer, Peer

    2011-04-20

    Vibrational circular dichroism (VCD) spectra were recorded with a tunable external-cavity quantum-cascade laser (QCL). In comparison with standard thermal light sources in the IR, QCLs provide orders of magnitude more power and are therefore promising for VCD studies in strongly absorbing solvents. The brightness of this novel light source is demonstrated with VCD and IR absorption measurements of a number of compounds, including proline in water.

  13. New experimental perspectives for soft x-ray absorption spectroscopies at ultra-low temperatures below 50 mK and in high magnetic fields up to 7 T

    NASA Astrophysics Data System (ADS)

    Beeck, T.; Baev, I.; Gieschen, S.; Meyer, H.; Meyer, S.; Palutke, S.; Feulner, P.; Uhlig, K.; Martins, M.; Wurth, W.

    2016-04-01

    A new ultra-low temperature experiment including a superconducting vector magnet has been developed for soft x-ray absorption spectroscopy experiments at third generation synchrotron light sources. The sample is cooled below 50 mK by a cryogen free 3He-4He dilution refrigerator. At the same time, magnetic fields of up to ±7 T in the horizontal direction and ±0.5 T in the vertical direction can be applied by a superconducting vector magnet. The setup allows to study ex situ and in situ prepared samples, offered by an attached UHV preparation chamber with load lock. The transfer of the prepared samples between the preparation section and the dilution refrigerator is carried out under cryogenic temperatures. First commissioning studies have been carried out at the Variable Polarization XUV Beamline P04 at PETRA III and the influence of the incident photon beam to the sample temperature has been studied.

  14. New experimental perspectives for soft x-ray absorption spectroscopies at ultra-low temperatures below 50 mK and in high magnetic fields up to 7 T.

    PubMed

    Beeck, T; Baev, I; Gieschen, S; Meyer, H; Meyer, S; Palutke, S; Feulner, P; Uhlig, K; Martins, M; Wurth, W

    2016-04-01

    A new ultra-low temperature experiment including a superconducting vector magnet has been developed for soft x-ray absorption spectroscopy experiments at third generation synchrotron light sources. The sample is cooled below 50 mK by a cryogen free (3)He-(4)He dilution refrigerator. At the same time, magnetic fields of up to ±7 T in the horizontal direction and ±0.5 T in the vertical direction can be applied by a superconducting vector magnet. The setup allows to study ex situ and in situ prepared samples, offered by an attached UHV preparation chamber with load lock. The transfer of the prepared samples between the preparation section and the dilution refrigerator is carried out under cryogenic temperatures. First commissioning studies have been carried out at the Variable Polarization XUV Beamline P04 at PETRA III and the influence of the incident photon beam to the sample temperature has been studied. PMID:27131716

  15. Anisotropic elliptical dichroism and influence of imperfection of circular polarization upon anisotropic circular dichroism

    SciTech Connect

    Wakabayashi, Masamitsu; Yokojima, Satoshi; Fukaminato, Tuyoshi; Ohtani, Hiroyuki; Nakamura, Shinichiro

    2015-04-21

    In spite of the importance of anisotropic circular dichroism, in practice, it is difficult to get rid of the artifacts that arise from the imperfection of the circular polarization. Undesirable linear dichroism, interference of two orthogonal polarization states, and linear birefringence prevent us from making accurate measurements. We propose a theoretical method for evaluating the contributions of the first two, which are thought to be the main artifacts when specimens are not thick enough. Using the time-dependent perturbation theory and taking into account the direction of light propagation toward an orientationally fixed molecule, we formulated the transition probability of systems perturbed by arbitrarily polarized light and the absorption difference associated with two kinds of polarized light. We also formulated, as an extension of the dissymmetry factor of circular dichroism, a newly defined dissymmetry factor associated with two arbitrary polarization states. Furthermore, we considered a mixed-state of photon ensemble in which polarization states distribute at a certain width around a certain average. Although the purity of polarization and ellipticity does not correspond immediately, by considering the mixed state it is possible to treat them consistently. We used quantum statistical mechanics to describe the absorption difference for two kinds of photon ensembles and applied the consequent formula to examine the reported experimental results of single-molecule chiroptical responses under discussion in the recent past. The artifacts are theoretically suggested to be sensitive to the incident direction of elliptically polarized light and to the oriented systems, the ellipticity, and the orientation of ellipse. The mixed state has little, if any, effect when the polarization state distribution is narrow.

  16. Anisotropic elliptical dichroism and influence of imperfection of circular polarization upon anisotropic circular dichroism

    NASA Astrophysics Data System (ADS)

    Wakabayashi, Masamitsu; Yokojima, Satoshi; Fukaminato, Tuyoshi; Ohtani, Hiroyuki; Nakamura, Shinichiro

    2015-04-01

    In spite of the importance of anisotropic circular dichroism, in practice, it is difficult to get rid of the artifacts that arise from the imperfection of the circular polarization. Undesirable linear dichroism, interference of two orthogonal polarization states, and linear birefringence prevent us from making accurate measurements. We propose a theoretical method for evaluating the contributions of the first two, which are thought to be the main artifacts when specimens are not thick enough. Using the time-dependent perturbation theory and taking into account the direction of light propagation toward an orientationally fixed molecule, we formulated the transition probability of systems perturbed by arbitrarily polarized light and the absorption difference associated with two kinds of polarized light. We also formulated, as an extension of the dissymmetry factor of circular dichroism, a newly defined dissymmetry factor associated with two arbitrary polarization states. Furthermore, we considered a mixed-state of photon ensemble in which polarization states distribute at a certain width around a certain average. Although the purity of polarization and ellipticity does not correspond immediately, by considering the mixed state it is possible to treat them consistently. We used quantum statistical mechanics to describe the absorption difference for two kinds of photon ensembles and applied the consequent formula to examine the reported experimental results of single-molecule chiroptical responses under discussion in the recent past. The artifacts are theoretically suggested to be sensitive to the incident direction of elliptically polarized light and to the oriented systems, the ellipticity, and the orientation of ellipse. The mixed state has little, if any, effect when the polarization state distribution is narrow.

  17. Astronomical sources of circularly polarized light and the origin of homochirality.

    PubMed

    Bailey, J

    2001-01-01

    Possible astronomical sources of ultraviolet circularly polarized light (UVCPL) which might be responsible for enantiomeric selection in interstellar organic molecules are considered, Synchrotron radiation from magnetic neutron stars has been suggested as a possible source of UVCPL. However, synchrotron radiation in these situations is not predicted to be strongly circularly polarized. Very few such sources show optical synchrotron radiation and in the few that do circular polarization has not been observed. Magnetic white dwarfs and white dwarf binaries (Polars) can be highly circularly polarized but any effect on molecular clouds and star formation regions must rely on rare chance encounters. Recent observations show that substantial levels of circular polarization are present in reflection nebulae in star formation regions. This mechanism produces polarized light exactly when and where it is needed in regions where star formation is occurring and organic molecules are known to be present.

  18. Astronomical sources of circularly polarized light and the origin of homochirality.

    PubMed

    Bailey, J

    2001-01-01

    Possible astronomical sources of ultraviolet circularly polarized light (UVCPL) which might be responsible for enantiomeric selection in interstellar organic molecules are considered, Synchrotron radiation from magnetic neutron stars has been suggested as a possible source of UVCPL. However, synchrotron radiation in these situations is not predicted to be strongly circularly polarized. Very few such sources show optical synchrotron radiation and in the few that do circular polarization has not been observed. Magnetic white dwarfs and white dwarf binaries (Polars) can be highly circularly polarized but any effect on molecular clouds and star formation regions must rely on rare chance encounters. Recent observations show that substantial levels of circular polarization are present in reflection nebulae in star formation regions. This mechanism produces polarized light exactly when and where it is needed in regions where star formation is occurring and organic molecules are known to be present. PMID:11296520

  19. Non-collinear generation of angularly isolated circularly polarized high harmonics

    NASA Astrophysics Data System (ADS)

    Hickstein, Daniel D.; Dollar, Franklin J.; Grychtol, Patrik; Ellis, Jennifer L.; Knut, Ronny; Hernández-García, Carlos; Zusin, Dmitriy; Gentry, Christian; Shaw, Justin M.; Fan, Tingting; Dorney, Kevin M.; Becker, Andreas; Jaroń-Becker, Agnieszka; Kapteyn, Henry C.; Murnane, Margaret M.; Durfee, Charles G.

    2015-11-01

    We generate angularly isolated beams of circularly polarized extreme ultraviolet light through the first implementation of non-collinear high harmonic generation with circularly polarized driving lasers. This non-collinear technique offers numerous advantages over previous methods, including the generation of higher photon energies, the separation of the harmonics from the pump beam, the production of both left and right circularly polarized harmonics at the same wavelength and the capability of separating the harmonics without using a spectrometer. To confirm the circular polarization of the beams and to demonstrate the practicality of this new light source, we measure the magnetic circular dichroism of a 20 nm iron film. Furthermore, we explain the mechanisms of non-collinear high harmonic generation using analytical descriptions in both the photon and wave models. Advanced numerical simulations indicate that this non-collinear mixing enables the generation of isolated attosecond pulses with circular polarization.

  20. Magnetization dynamics in La{sub 0.67}Ca{sub 0.33}MnO{sub 3} epitaxial films probed with resonant and non-resonant microwave absorption

    SciTech Connect

    Porwal, Rajni; Pant, R. P.; Budhani, R. C.

    2015-01-07

    Temperature (T) dependent microwave absorption measurements are performed on La{sub 0.67}Ca{sub 0.33}MnO{sub 3} (LCMO) epitaxial thin films of thickness 100 and 200 nm in an electron paramagnetic resonance spectrometer operating in X-band. The resonant absorption peak is monitored for out-of-plane (H{sup ⊥}) and in-plane (H{sup ∥}) dc magnetic field (H) as the system goes through magnetic ordering. These data suggest a resilient transformation to the ferromagnetic (FM) phase in the vicinity of the Curie temperature (T{sub C}), indicative of a phase separation, which is dominant in the thinner film. The saturation magnetization is calculated from SQUID magnetometry on the same film. A pronounced zero-field absorption is seen in H{sup ∥} geometry displaying anomalous growth in 100 nm film at T < T{sub C}. This feature is correlated with the magneto-conductivity of the manganite which is colossal in the vicinity of T{sub C} in the well-ordered film of thickness 200 nm. Signature of standing spin wave modes is seen in H{sup ⊥} measurements which are analyzed to calculate the spin wave stiffness constant D(T) in the limit of zero temperature. The same is also inferred from the decay of equilibrium magnetization in the framework of Bloch law. These studies reveal that a bulk like LCMO is obtained in the fully relaxed thicker films.

  1. Generation of circular polarization of gamma ray bursts

    NASA Astrophysics Data System (ADS)

    Batebi, S.; Mohammadi, R.; Ruffini, R.; Tizchang, S.; Xue, S.-S.

    2016-09-01

    The generation of the circular polarization of gamma ray burst (GRB) photons is discussed in this paper via their interactions with astroparticles in the presence or absence of background fields such as magnetic fields and noncommutative space-time geometry. Solving the quantum Boltzmann equation for GRB photons as a photon ensemble, we discuss the generation of circular polarization (as Faraday conversion phase shift Δ ϕFC) of GRBs in the following cases: (i) intermediate interactions, i.e., the Compton scattering of GRBs in the galaxy cluster magnetic field and in the presence of noncommutative space-time geometry, as well as the scattering of GRBs in the cosmic neutrino background (CNB) and cosmic microwave background (CMB); (ii) interactions with particles and fields in shockwaves, i.e., the Compton scattering of GRBs with accelerated charged particles in the presence of magnetic fields. We found that (i) after shockwave crossing, the greatest contribution of Δ ϕFC for energetic GRBs (of the order of GeV and larger) comes from GRB-CMB interactions, but for low-energy GRBs the contributions of the Compton scattering of GRBs in the galaxy cluster magnetic field dominate; (ii) in shockwave crossing, the magnetic field has significant effects on converting a GRB's linear polarization to a circular one, and this effect can be used to better understand the magnetic profile in shockwaves. The main aim of this work is to study and measure the circular polarization of GRBs for a better understanding of the physics and mechanism of the generation of GRBs and their interactions before reaching us.

  2. Selenium speciation using capillary electrophoresis coupled with modified electrothermal atomic absorption spectrometry after selective extraction with 5-sulfosalicylic acid functionalized magnetic nanoparticles.

    PubMed

    Yan, Lizhen; Deng, Biyang; Shen, Caiying; Long, Chanjuan; Deng, Qiufen; Tao, Chunyao

    2015-05-22

    A new method for selenium speciation in fermented bean curd wastewater and juice was described. This method involved sample extraction with 5-sulfosalicylic acid (SSA)-functionalized silica-coated magnetic nanoparticles (SMNPs), capillary electrophoresis (CE) separation, and online detection with a modified electrothermal atomic absorption spectrometry (ETAAS) system. The modified interface for ETAAS allowed for the introduction of CE effluent directly through the end of the graphite tube. Elimination of the upper injection hole of the graphite tube reduced the loss of the anlayte and enhanced the detection sensitivity. The SSA-SMNPs were synthesized and used to extract trace amounts of selenite [Se(IV)], selenite [Se(VI)], selenomethionine (SeMet), and selenocystine (SeCys2) from dilute samples. The concentration enrichment factors for Se(VI), Se(IV), SeMet, and SeCys2 were 21, 29, 18, and 12, respectively, using the SSA-SMNPs extraction. The limits of detection for Se(VI), Se(IV), SeMet, and SeCys2 were 0.18, 0.17, 0.54, 0.49ngmL(-1), respectively. The RSD values (n=6) of method for intraday were observed between 0.7% and 2.9%. The RSD values of method for interday were less than 3.5%. The linear range of Se(VI) and Se(IV) were in the range of 0.5-200ngmL(-1), and the linear ranges of SeMet and SeCys2 were 2-500 and 2-1000ngmL(-1), respectively. The detection limits of this method were improved by 10 times due to the enrichment by the SSA-SMNP extraction. The contents of Se(VI) and Se(IV) in fermented bean curd wastewater were measured as 3.83 and 2.62ngmL(-1), respectively. The contents of Se(VI), Se(IV), SeMet, and SeCys2 in fermented bean curd juice were determined as 6.39, 4.08, 2.77, and 4.00ngmL(-1), respectively. The recoveries were in the range of 99.14-104.5% and the RSDs (n=6) of recoveries between 0.82% and 3.5%.

  3. Circular dichroism in the electron microscope: Progress and applications (invited)

    SciTech Connect

    Schattschneider, P.; Loeffler, S.; Ennen, I.; Stoeger-Pollach, M.; Verbeeck, J.

    2010-05-15

    According to theory, x-ray magnetic circular dichroism in a synchrotron is equivalent to energy loss magnetic chiral dichroism (EMCD) in a transmission electron microscope (TEM). After a synopsis of the development of EMCD, the theoretical background is reviewed and recent results are presented, focusing on the study of magnetic nanoparticles for ferrofluids and Heusler alloys for spintronic devices. Simulated maps of the dichroic strength as a function of atom position in the crystal allow evaluating the influence of specimen thickness and sample tilt on the experimental EMCD signal. Finally, the possibility of direct observation of chiral electronic transitions with atomic resolution in a TEM is discussed.

  4. Circular polarization interferometry: circularly polarized modes of cholesteric liquid crystals.

    PubMed

    Sanchez-Castillo, A; Eslami, S; Giesselmann, F; Fischer, P

    2014-12-15

    We describe a novel polarization interferometer which permits the determination of the refractive indices for circularly-polarized light. It is based on a Jamin-Lebedeff interferometer, modified with waveplates, and permits us to experimentally determine the refractive indices nL and nR of the respectively left- and right-circularly polarized modes in a cholesteric liquid crystal. Whereas optical rotation measurements only determine the circular birefringence, i.e. the difference (nL - nR), the interferometer also permits the determination of their absolute values. We report refractive indices of a cholesteric liquid crystal in the region of selective (Bragg) reflection as a function of temperature. PMID:25607071

  5. Circular structures of Bajada del Diablo (Argentina): geophysical signatures

    NASA Astrophysics Data System (ADS)

    Prezzi, C. B.; Orgeira, M. J.; Martinez, O.; Acevedo, R. D.; Ponce, F.; Goldmann, G.; Magneres, I.; Rabassa, J.

    2016-05-01

    Bajada del Diablo is located in the Northern Patagonian Massif, Chubut, Argentina. The study area includes several circular structures found in Miocene olivine basalts of the Quiñelaf Eruptive Complex and in the Late Pliocene/Early Pleistocene Pampa Sastre conglomerates. An impact origin has been proposed for these circular structures. With the aim of further investigate the proposed impact origin, topographic, gravimetric, magnetic, resistivity, palaeomagnetic and electromagnetic surveys in two circular structures (`8' and `G') located in Pampa Sastre conglomerates and in basalts of the Quiñelaf Eruptive Complex were carried out. The new geophysical results support the hypothesis of an impact origin. However, the confirmation of such an origin through the findings of shock metamorphism evidences and/or the recovery of meteorites remains elusive.

  6. MAGNETS

    DOEpatents

    Hofacker, H.B.

    1958-09-23

    This patent relates to nmgnets used in a calutron and more particularly to means fur clamping an assembly of magnet coils and coil spacers into tightly assembled relation in a fluid-tight vessel. The magnet comprises windings made up of an assembly of alternate pan-cake type coils and spacers disposed in a fluid-tight vessel. At one end of the tank a plurality of clamping strips are held firmly against the assembly by adjustable bolts extending through the adjacent wall. The foregoing arrangement permits taking up any looseness which may develop in the assembly of coils and spacers.

  7. Circular codes, symmetries and transformations.

    PubMed

    Fimmel, Elena; Giannerini, Simone; Gonzalez, Diego Luis; Strüngmann, Lutz

    2015-06-01

    Circular codes, putative remnants of primeval comma-free codes, have gained considerable attention in the last years. In fact they represent a second kind of genetic code potentially involved in detecting and maintaining the normal reading frame in protein coding sequences. The discovering of an universal code across species suggested many theoretical and experimental questions. However, there is a key aspect that relates circular codes to symmetries and transformations that remains to a large extent unexplored. In this article we aim at addressing the issue by studying the symmetries and transformations that connect different circular codes. The main result is that the class of 216 C3 maximal self-complementary codes can be partitioned into 27 equivalence classes defined by a particular set of transformations. We show that such transformations can be put in a group theoretic framework with an intuitive geometric interpretation. More general mathematical results about symmetry transformations which are valid for any kind of circular codes are also presented. Our results pave the way to the study of the biological consequences of the mathematical structure behind circular codes and contribute to shed light on the evolutionary steps that led to the observed symmetries of present codes. PMID:25008961

  8. Circularly Polarized Light and Growth of Plants

    NASA Astrophysics Data System (ADS)

    Shibayev, Pavel; Pergolizzi, Robert

    2011-03-01

    The influence of linearly polarized light on the direction of plants growth has been recently demonstrated. The state of circularly polarized (CP) light can also change when it is reflected from the surface of leaves and stems. However, the role of light handedness in the development of plants and CP light interaction with the complexes of chlorophyll molecules have still not been studied enough. In this work, the role of left CP light in the accelerated growth of lentil and pea plants is revealed and studied. The mechanism of such an enhancement is discussed in terms of the model considering transmission, absorption, and scattering of CP light on micro and macro levels of leaf organization. Theoretical modeling of light interaction with the interior of the leaf was conducted for a number of recently proposed models of organization of chlorophyll molecules and chloroplasts. All the calculations were performed by employing a 4x4 matrix method in solving Maxwell equations. It is shown that left-handed chiral organization of chlorophyll molecules can greatly enhance the absorption of light and therefore lead to the enhanced growth of the whole plant under CP light.

  9. Circular birefringence of banded spherulites.

    PubMed

    Cui, Xiaoyan; Shtukenberg, Alexander G; Freudenthal, John; Nichols, Shane; Kahr, Bart

    2014-04-01

    Crystal optical properties of banded spherulites of 21 different compounds--molecular crystals, polymers, and minerals--with helically twisted fibers were analyzed with Mueller matrix polarimetry. The well-established radial oscillations in linear birefringence of many polycrystalline ensembles is accompanied by oscillations in circular birefringence that cannot be explained by the natural optical activity of corresponding compounds, some of which are centrosymmetric in the crystalline state. The circular birefringence is shown to be a consequence of misoriented, overlapping anisotropic lamellae, a kind of optical activity associated with the mesoscale stereochemistry of the refracting components. Lamellae splay as a consequence of space constraints related to simultaneous twisting of anisometric lamellae. This mechanism is supported by quantitative simulations of circular birefringence arising from crystallite twisting and splaying under confinement. PMID:24625095

  10. Absorption and emission in defective cholesteric liquid crystal cells

    NASA Astrophysics Data System (ADS)

    Gevorgyan, A. H.; Harutyunyan, M. Z.; Matinyan, G. K.; Oganesyan, K. B.; Rostovtsev, Yu V.; Kurizki, G.; Scully, M. O.

    2016-04-01

    We investigated peculiarities of absorption, emission and photonic density of states of a cholesteric liquid crystal with an isotropic defect layer inside. The influence of the defect layer position on absorption and emission in the system was studied. It was shown that for non-diffracting circularly polarized incident light absorption/emission is maximum if the defect is in the centre of the system; and for diffracting circularly polarized incident light absorption/emission is maximum if the defect is shifted from the centre of the system to its left border from where light is incident. We also investigated influence of the defect layer thickness and those parameters which characterize loss and gain on absorption and emission. The influence of anisotropic absorption in the cholesteric liquid crystal layer on photonic density states was investigated, too.

  11. Geophysical characterization of circular structures in Chubut and Mendoza (Argentina): Impact vs. Volcanism

    NASA Astrophysics Data System (ADS)

    Prezzi, C.; Orgeira, M. J.; Risso, C.; Acevedo, R.; Ponce, F.; Nullo, F.; Martinez, O.; Rabassa, J.; Margonari, L.; Corbella, H.

    2013-05-01

    This work focuses on two main objectives. One of them is to provide information to discern the genesis of the circular structures present in Bajada del Diablo (Chubut, Argentina) considered as impact craters, and the other one is to contribute to a better knowledge of the circular structures located in the volcanic fields of Llancanelo and Payunia (Mendoza, Argentina). Chubut circular structures have been attributed to the collision of an extraterrestrial body, possibly an asteroid. However, doubts persist about their genesis because of the lack of direct geological evidences. Since detailed geomorphological studies have ruled out an origin by wind deflation, the prevailing alternative hypothesis attributes these circular structures to a volcanic process. On the other hand, the study of the volcanic fields of Payunia and Llancanelo (Mendoza) will contribute to the knowledge of the mechanics of hydromagmatic processes in the area, and the origin of circular structures morphologically similar to those located in Chubut. In the Payunia volcanic field at least 27 cones with evidences of hydromagmatism, in a field of more than 800 pure magmatic cones, have been recognized. This study tries to determine if a relationship between the observed volcanic circular structures and participation of water during the eruption exists. Magnetic and gravity field surveys of the circular volcanic structures in Llancanelo and Payunia volcanic fields were performed in order to determine their relationship with the type of eruption. Electromagnetic, magnetic and gravity field surveys were also carried out in Chubut circular structures. The comparative analysis of geological and geophysical results obtained in the circular structures of Chubut and those obtained in the circular structures in the volcanic areas of Llancanelo and Payunia suggest an impact origin for the circular structures of Chubut.

  12. Feige 7 - A hot, rotating magnetic white dwarf

    NASA Technical Reports Server (NTRS)

    Liebert, J.; Angel, J. R. P.; Stockman, H. S.; Spinrad, H.; Beaver, E. A.

    1977-01-01

    Results are reported for image-tube-scanner and digicon observations of Feige 7, a faint blue star identified as a probable white dwarf. It is found that this star is a magnetic white dwarf showing a very rich spectrum with Zeeman subcomponents of both hydrogen and neutral helium as well as periodic spectrum and circular-polarization variations. A polarization period of 2.2 hr is computed, and a surface magnetic-field strength of about 18 MG is determined by matching features of the absorption spectrum to Zeeman components. It is suggested that the only reasonable explanation for the periodic variations in circular polarization is an oblique rotator with the spin axis approximately in the plane of the sky and tilted by about 24 deg to the magnetic axis. An effective temperature in the range from 20,000 to 25,000 K is estimated, an absolute magnitude of about 10.5 is derived, and the atmosphere is shown to be helium-dominated. The evolution of Feige 7 is discussed in terms of possible magnetic-field effects on atmospheric composition, rotation velocity (5.5 km/s for a radius of 7000 km), and the origin of white-dwarf magnetic fields.

  13. Circular RNA expands its territory.

    PubMed

    Bao, Chunyang; Lyu, Dongbin; Huang, Shenglin

    2016-03-01

    Circular RNAs (circRNAs) represent a novel class of widespread non-coding RNAs in eukaryotes. They are unusually stable RNA molecules with cell type-specific expression patterns, and are predominantly present in the cytoplasm. We recently demonstrated the existence of abundant circRNAs in exosomes and suggest a potential application of exosomal circRNAs for cancer detection. PMID:27308606

  14. Class IIc or Circular Bacteriocins

    NASA Astrophysics Data System (ADS)

    Martin-Visscher, Leah A.; van Belkum, Marco J.; Vederas, John C.

    The circular bacteriocins produced by Gram-positive bacteria represent a diverse class of antimicrobial peptides. These bacteriocins display enhanced stability compared to linear bacteriocins, which arises from their characteristic circular backbone. Currently, eight unique circular bacteriocins have been identified, and analysis of their gene clusters indicates that they likely utilize complex mechanisms for maturation and secretion, as well as for immunity. These bacteriocins target the cytoplasmic membrane of sensitive cells, leading to pore formation that results in loss of ions, dissipation of membrane potential, and ultimately, cell death. Structural studies suggest that despite variation in their sequences, most of these bacteriocins likely adopt a common three-dimensional architecture, consisting of four or five tightly packed helices encompassing a hydrophobic core. There are many mysteries surrounding the biosynthesis of these peptides, particularly in regard to the mechanism by which they are cyclized. Elucidation of such a mechanism may provide exciting new approaches to the bioengineering of new, stable, and antimicrobially active circular peptides.

  15. A tool for symmetry studies in circular machines

    SciTech Connect

    Bozoki, E.

    1988-05-01

    The use of the C (mrad/Amp) conversion factors of the orbit corrector magnets in the sudy of the symmetry properties of a circular accelerator or storage ring, and in the determination of the ratios of the ..beta..-functions at corrector locations is discussed. Measurements obtained for the VUV and x-ray rings of the NSLS at Brookhaven National Laboratory are presented. 4 refs., 7 figs., 3 tabs.

  16. Preparation of circular Rydberg states in helium using the crossed-fields method

    NASA Astrophysics Data System (ADS)

    Zhelyazkova, V.; Hogan, S. D.

    2016-08-01

    Helium atoms have been prepared in the circular |n =55 ,ℓ =54 , mℓ=+54 > Rydberg state using the crossed electric and magnetic fields method. The atoms, initially traveling in pulsed supersonic beams, were photoexcited from the metastable 1 s 2 s S31 level to the outermost, mℓ=0 Rydberg-Stark state with n =55 in the presence of a strong electric field and weak perpendicular magnetic field. Following excitation, the electric field was adiabatically switched off causing the atoms to evolve into the circular state with mℓ=+54 defined with respect to the magnetic-field quantization axis. The circular states were detected by ramped electric-field ionization along the magnetic-field axis. The dependence of the circular state production efficiency on the strength of the excitation electric field, and the electric-field switch-off time was studied, and microwave spectroscopy of the circular-to-circular |55 ,54 ,+54 >→|56 ,55 ,+55 > transition at ˜38.5 GHz was performed.

  17. Near infrared absorption spectra of C{sub 60} radical cations and anions prepared simultaneously in solid argon

    SciTech Connect

    Schatz, P.N.; Gasyna, Z.; Andrews, L.

    1992-12-01

    The codeposition of C{sub 60} vapor with excess argon and concurrent argon resonance radiation has produced strong new absorptions at 973 and 1068 nm in solid argon at 11 {plus_minus} 1 K. A similar experiment with CCl{sub 4}, added to serve as an electron trap, reduced the yield of the 1068 nm band with little effect on the 973 nm absorption. The 973 nm band is assigned to C{sub 60}{sup +} produced by photoionization and the 1068 nm band to C{sub 60}{sup {minus}} formed by electron capture. These identifications are in excellent agreement with glassy matrix, solution and photoelectron spectra. Preliminary magnetic circular dichroism (MCD) spectra of the 973 nm C{sub 60}{sup +} band have also been measured. Both the 1068 and 973 nm bands show a characteristic triplet structure which is tentatively attributed to the combined effects of spin-orbit and Jahn-Teller coupling.

  18. Transformation of electromagnetically induced transparency into absorption in a thermal potassium optical cell with spin preserving coating

    NASA Astrophysics Data System (ADS)

    Gozzini, S.; Lucchesini, A.; Marinelli, C.; Marmugi, L.; Gateva, S.; Tsvetkov, S.; Cartaleva, S.

    2016-03-01

    We report a new experimental approach where an order of magnitude enhancement of the electromagnetically induced absorption (EIA) resonance contrast, thus making it similar to that of the EIT resonance contrast is observed under the same conditions. The EIA signal results from the interaction of a weak probe beam with a ground state that has been driven by the pump (counter-propagating) beam. Probe absorption spectra are presented where the laser frequency is slowly detuned over the D1 line of 39K vapor contained in a cell with a PDMS antirelaxation coating. In addition to the frequency detuning, a magnetic field orthogonal to the laser beams is scanned around zero value at a higher rate. With both laser beams linearly polarized, an EIT resonance is observed. However, changing the pump beam polarization from linear to circular reverses the resonance signal from EIT to EIA.

  19. LINEAR AND CIRCULAR DICHROISM OF MEMBRANES FROM RHODOPSEUDOMONAS CAPSULATA

    SciTech Connect

    Bolt, John D.; Sauer, Kenneth; Shiozawa, Judith A.; Drews, Gerhart

    1980-10-01

    Absorption, linear dichroism and circular dichroism spectra of Rhodopseudomonas capsulate (wild-type - St. Louis strain, mutant Y5 and mutant A1a{sup +}) are particularly sensitive to the nature of the light-harvesting bacteriochlorophyll-carotenoid-protein complexes. Evidence for exciton-type interactions is seen near 855 nm in the membranes from the wild-type and from mutant Y5, as well as in an isolated B800+850 light-harvesting complex from mutant Y5. The strong circular dichroism that reflects these interactions is attenuated more than 10-fold in membranes from the A1a+ mutant, which lacks both B800+850 and colored carotenoids and contains only the B875 light-harvesting complex. These results lead to the conclusion that these two light-harvesting complexes have significantly different chromophore arrangements or local environments.

  20. Geophysical characterization of two circular structures at Bajada del Diablo (Patagonia, Argentina): Indication of impact origin

    NASA Astrophysics Data System (ADS)

    Prezzi, Claudia B.; Orgeira, María Julia; Acevedo, Rogelio D.; Ponce, Juan Federico; Martinez, Oscar; Rabassa, Jorge O.; Corbella, Hugo; Vásquez, Carlos; González-Guillot, Mauricio; Subías, Ignacio

    2012-02-01

    An impact origin has been proposed for the circular structures found in Bajada del Diablo, Patagonia, Argentina. Taking into account its extension and the number of impact structures, Bajada del Diablo would be the largest meteoritic impact areas known on Earth, being an extremely interesting area for the research of impact events and processes. Moreover, the global distribution of known impact structures shows a surprising asymmetry. Particularly, South America has only seven described areas. It is evident that this situation is an artifact, highlighting the importance of intensifying the research in the least studied areas such as Argentina. Circular structures in Bajada del Diablo have been identified on two rock types: the Quiñelaf eruptive complex and Pampa Sastre Formation. In the first case, circular structures are placed in olivine basalts. On the other hand, Pampa Sastre Formation (late Pliocene/early Pleistocene) corresponds to conglomerate layers with basalt clasts boulder and block in size in a coarse sandy matrix. With the aim of further the investigation of the proposed impact origin for these circular structures, we carried out detailed topographic, magnetic and electromagnetic ground surveys in two circular structures ("8" and "A") found in Pampa Sastre conglomerates. Both circular structures are simple, bowl-shaped with rim diameters of 300 m and maximum depths of 10 m. They have been partially filled in by debris flows from the rims and wind-blown sands. Two preliminary magnetic profiles have also been carried out in circular structure "G" found in Quiñelaf basalts. The magnetic anomalies show a circular pattern with a slightly negative and relatively flat signal in the circular structures' bases. Furthermore in the circular structures' rims, high-amplitude, conspicuous and localized (short wavelength) anomalies are observed. Such large amplitude and short wavelength anomalies are not detected outside the circular structures. For all used

  1. High-accuracy linear and circular polarization measurements at 21 cm

    NASA Technical Reports Server (NTRS)

    De Pater, I.; Weiler, K. W.

    1982-01-01

    New high-accuracy linear and circular polarization measurements have been obtained for 27 small-diameter radio sources, using the Westerbork Synthesis Radio Telescope at 21 cm (1415 MHz). From these and other observed properties of the sources, estimates of the average internal magnetic field strengths in the sources are made by applying the uniform synchrotron emission model to the measured circular polarization and by using equipartition arguments. These two values are compared and found to be in agreement to within an order of magnitude, as was previously found by Weiler and de Pater (1980). Also, the magnetic fields estimated from circular polarization measurements at two different wavelengths (49 and 21 cm) are compared and found to be in rough agreement, but with indications of differences between variable and nonvariable sources. A comparison of the magnitudes of linear and circular polarization in sources shows no correlations.

  2. Mg II ABSORPTION SYSTEMS WITH W{sub 0} >= 0.1 A FOR A RADIO SELECTED SAMPLE OF 77 QUASI-STELLAR OBJECTS AND THEIR ASSOCIATED MAGNETIC FIELDS AT HIGH REDSHIFT

    SciTech Connect

    Bernet, M. L.; Miniati, F.; Lilly, S. J. E-mail: fm@phys.ethz.c

    2010-03-01

    We present a catalog of Mg II absorption systems obtained from high-resolution Ultraviolet and Visual Echelle Spectrograph/VLT data of 77 quasi-stellar objects in the redshift range 0.6 < z < 2.0, and down to an equivalent width W{sub 0} >= 0.1 A. The statistical properties of our sample are found to be in agreement with those from the previous work in the literature. However, we point out that the previously observed increase with redshift of partial derivN/partial derivz for weak absorbers pertains exclusively to very weak absorbers with W{sub 0} < 0.1 A. Instead, partial derivN/partial derivz for absorbers with W{sub 0} in the range 0.1-0.3 A actually decreases with redshift, similar to the case of strong absorbers. We then use this catalog to extend our earlier analysis of the links between the Faraday rotation measure (RM) of the quasars and the presence of intervening Mg II absorbing systems in their spectra. In contrast to the case with strong Mg II absorption systems (W{sub 0} > 0.3 A), the weaker systems do not contribute significantly to the observed RM of the background quasars. This is possibly due to the higher impact parameters of the weak systems compared to strong ones, suggesting that the high column density magnetized material that is responsible for the Faraday rotation is located within about 50 kpc of the galaxies. Finally, we show that this result also rules out the possibility that some unexpected secondary correlation between the quasar redshift and its intrinsic RM is responsible for the association of high RM and strong intervening Mg II absorption that we have presented elsewhere, since this would have produced an equal effect for the weak absorption line systems, which exhibit a very similar distribution of quasar redshifts.

  3. Nonlinear Vibration of a Magnetic Spring

    ERIC Educational Resources Information Center

    Zhong, Juhua; Cheng, Zhongqi; Ge, Ziming; Zhang, Yuelan; Lu, Wenqiang; Song, Feng; Li, Chuanyong

    2012-01-01

    To demonstrate the different vibration characteristics of a magnetic spring compared with those of a metal one, a magnetic spring apparatus was constructed from a pair of circular magnets of the same size with an inside diameter of 2.07 cm and an outside diameter of 4.50 cm. To keep the upper magnet in a suspension state, the two magnets were…

  4. Circular on planned parenthood, 1987.

    PubMed

    1987-01-01

    In 1987 fourteen units of the Government of Henan issued a Circular stating that: "Planned parenthood must be publicized deep into the grass roots and among the people, and importance must be attached to results." The Circular stresses: "In the propaganda drive, it is necessary to successfully grasp three key links: 1. It is necessary to disseminate intensively the important directive on population problems that is contained in the report of the 13th CPC National Congress and the seriousness of the population situation of our country and province so that the cadres and the masses can understand the relationship between population control and the achievement of the strategic target of the three big steps, understand the reason for carrying out planned parenthood, understand that the one-child policy is still advocated, and conscientiously carry out planned parenthood. 2. It is essential to succeed in propagating knowledge of contraception, sterilization, childbirth, and child care and in conducting ideological education for those who undergo operations and for their family members. 3. It is imperative to visit those who have undergone operations and to help them solve practically their difficulties in making a living." The Circular concludes by demanding that under the unified leadership of party committees and governments at all levels, the propaganda drive be carried out by relying on the efforts of all of society. In conjunction with their own work, departments, including the propaganda, education, public health, and cultural departments, must carry out propaganda and education for planned parenthood.

  5. Interstellar circular polarization and the dielectric nature of dust grains

    NASA Technical Reports Server (NTRS)

    Chlewicki, Grzegorz; Greenberg, J. Mayo

    1989-01-01

    The implications of the observed relationship between the wavelength dependence of interstellar circular and linear polarization were reexamined. Mie theory calculations for grains with various optical constants demonstrate that any population of grains which matches the observed wavelength dependence of linear polarization also yields the correct cross-over wavelength of circular polarization. The coincidence of the peak wavelength of linear polarization and the cross-over of circular polarization is therefore independent of the optical constants of the grains and cannot be used as a critical constraint on grain properties. The observed relationship instead reflects a more fundamental connection between linear and circular polarization which was derived from the Kramers-Kronig relations by Shapiro (1975). Numerical results fully support Shapiro's conclusions and demonstrate that the apparent upper limit on the visual absorptivity of polarizing grains deduced from earlier Mie theory calculations (Martin, 1972) was spurious and resulted from a violation of the Kramers-Kronig relations in the assumed optical constants of the particles. The Kramers-Kronig interpretation of circular polarization can be used to place constraints on linear polarization outside the wavelength range in which it was observed. This approach was used to show that the peak observed in the visual is likely to be the only significant feature in the linear polarization curve, which therefore appears to be well approximated at all wavelengths by the Serkowski formula. A synthesis of available laboratory data was used to analyze the properties of dielectric core-mantel grains as the source of visual extinction and polarization.

  6. Direct surface magnetometry with photoemission magnetic x-ray dichroism

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Schumann, F.O.

    1997-04-01

    Element specific surface magnetometry remains a central goal of synchrotron radiation based studies of nanomagnetic structures. One appealing possibility is the combination of x-ray absorption dichroism measurements and the theoretical framework provided by the {open_quotes}sum rules.{close_quotes} Unfortunately, sum rule analysis are hampered by several limitations including delocalization of the final state, multi-electronic phenomena and the presence of surface dipoles. An alternative experiment, Magnetic X-Ray Dichroism in Photoelectron Spectroscopy, holds out promise based upon its elemental specificity, surface sensitivity and high resolution. Computational simulations by Tamura et al. demonstrated the relationship between exchange and spin orbit splittings and experimental data of linear and circular dichroisms. Now the authors have developed an analytical framework which allows for the direct extraction of core level exchange splittings from circular and linear dichroic photoemission data. By extending a model initially proposed by Venus, it is possible to show a linear relation between normalized dichroism peaks in the experimental data and the underlying exchange splitting. Since it is reasonable to expect that exchange splittings and magnetic moments track together, this measurement thus becomes a powerful new tool for direct surface magnetometry, without recourse to time consuming and difficult spectral simulations. The theoretical derivation will be supported by high resolution linear and circular dichroism data collected at the Spectromicroscopy Facility of the Advanced Light Source.

  7. The Panther Mountain circular structure, a possible buried meteorite crater

    NASA Astrophysics Data System (ADS)

    Isachsen, Y. W.; Wright, S. F.; Revetta, F. A.; Duneen, R. J.

    Panther Mountain, located near Phoenicia, New York, is part of the Catskill Mountains, which form the eastern end of the Allegheny Plateau in New York. It is a circular mass defined physiographically by an anomalous circular drainage pattern produced by Esopus Creek and its tributary Woodland Creek. The circular valley that rings the mountain is fracture-controlled; where bedrock is exposed, it shows a joint density 5 to 10 times greater than that on either side of the valley. Where obscured by alluvial valley fill, the bedrock's low seismic velocity suggests that this anomalous fracturing is continuous in the bedrock underlying the rim valley. North-south and east-west gravity and magnetic profiles were made across the structure. Terrane-corrected, residual gravity profiles show an 18-mgal negative anomaly, and very steep gradients indicate a near-surface source. Several possible explanations of the gravity data were modeled. We conclude that the Panther Mountain circular structure is probably a buried meteorite crater that formed contemporaneously with marine or fluvial sedimentation during Silurian or Devonian time. An examination of drill core and cuttings in the region is underway to search for ejecta deposits and possible seismic and tsunami effects in the sedimentary section. Success would result in both dating the impact and furnishing a chronostratigraphic marker horizon.

  8. General description of circularly symmetric Bessel beams of arbitrary order

    NASA Astrophysics Data System (ADS)

    Wang, Jia Jie; Wriedt, Thomas; Lock, James A.; Mädler, Lutz

    2016-11-01

    A general description of circularly symmetric Bessel beams of arbitrary order is derived in this paper. This is achieved by analyzing the relationship between different descriptions of polarized Bessel beams obtained using different approaches. It is shown that a class of circularly symmetric Davis Bessel beams derived using the Hertz vector potentials possesses the same general functional dependence as the aplanatic Bessel beams generated using the angular spectrum representation (ASR). This result bridges the gap between different descriptions of Bessel beams and leads to a general description of circularly symmetric Bessel beams, such that the Davis Bessel beams and the aplanatic Bessel beams are merely the two simplest cases of an infinite number of possible circularly symmetric Bessel beams. Additionally, magnitude profiles of the electric and magnetic fields, the energy density and the Poynting vector are displayed for Bessel beams in both paraxial and nonparaxial cases. The results presented in this paper provide a fresh perspective on the description of Bessel beams and cast some insights into the light scattering and light-matter interactions problems in practice.

  9. The Panther Mountain circular structure, a possible buried meteorite crater

    NASA Technical Reports Server (NTRS)

    Isachsen, Y. W.; Wright, S. F.; Revetta, F. A.; Duneen, R. J.

    1992-01-01

    Panther Mountain, located near Phoenicia, New York, is part of the Catskill Mountains, which form the eastern end of the Allegheny Plateau in New York. It is a circular mass defined physiographically by an anomalous circular drainage pattern produced by Esopus Creek and its tributary Woodland Creek. The circular valley that rings the mountain is fracture-controlled; where bedrock is exposed, it shows a joint density 5 to 10 times greater than that on either side of the valley. Where obscured by alluvial valley fill, the bedrock's low seismic velocity suggests that this anomalous fracturing is continuous in the bedrock underlying the rim valley. North-south and east-west gravity and magnetic profiles were made across the structure. Terrane-corrected, residual gravity profiles show an 18-mgal negative anomaly, and very steep gradients indicate a near-surface source. Several possible explanations of the gravity data were modeled. We conclude that the Panther Mountain circular structure is probably a buried meteorite crater that formed contemporaneously with marine or fluvial sedimentation during Silurian or Devonian time. An examination of drill core and cuttings in the region is underway to search for ejecta deposits and possible seismic and tsunami effects in the sedimentary section. Success would result in both dating the impact and furnishing a chronostratigraphic marker horizon.

  10. Water absorption in mortar determined by NMR.

    PubMed

    Pel, L; Hazrati, K; Kopinga, K; Marchand, J

    1998-01-01

    Nuclear magnetic resonance (NMR) offers the possibility to determine moisture profiles in porous building materials. Moreover, the relaxation of the nuclear magnetic resonance signal can provide additional information on the water distribution in the microstructure. For mortar, it is shown that the transverse relaxation yields information on the distribution of water in the gel pores and capillary pores. Moisture profiles and relaxation were measured during water absorption. The effect of the drying treatment on the microstructure and the water absorption was investigated.

  11. X-ray photoemission electron microscopy, a tool for the investigation of complex magnetic structures.

    SciTech Connect

    Scholl, Andreas; Ohldag, Hendrik; Nolting, Frithjof; Stohr, Joachim; Padmore, Howard A.

    2001-08-30

    X-ray Photoemission Electron Microscopy unites the chemical specificity and magnetic sensitivity of soft x-ray absorption techniques with the high spatial resolution of electron microscopy. The discussed instrument possesses a spatial resolution of better than 50 nm and is located at a bending magnet beamline at the Advanced Light Source, providing linearly and circularly polarized radiation between 250 and 1300 eV. We will present examples which demonstrate the power of this technique applied to problems in the field of thin film magnetism. The chemical and elemental specificity is of particular importance for the study of magnetic exchange coupling because it allows separating the signal of the different layers and interfaces in complex multi-layered structures.

  12. Magnetism and electronic structure of YTiO{sub 3} thin films

    SciTech Connect

    Cao, Yanwei Liu, Xiaoran; Meyers, D.; Kareev, M.; Middey, S.; Chakhalian, J.; Shafer, P.; Arenholz, E.; Freeland, J. W.

    2015-09-14

    High-quality (001)-oriented (pseudo-cubic notation) ferromagnetic YTiO{sub 3} thin films were epitaxially synthesized in a layer-by-layer way by pulsed laser deposition. Structural, magnetic, and electronic properties were characterized by reflection-high-energy-electron-diffraction, X-ray diffraction, vibrating sample magnetometry, and element-resolved resonant soft X-ray absorption spectroscopy. To reveal ferromagnetism of the constituent titanium ions, X-ray magnetic circular dichroism spectroscopy was carried out using four detection modes probing complementary spatial scale, which overcomes a challenge of probing ferromagnetic titanium with pure Ti{sup 3+}(3d{sup 1}). Our work provides a pathway to distinguish between the roles of titanium and A-site magnetic rare-earth cations in determining the magnetism in rare-earth titanates thin films and heterostructures.

  13. Synchronous (Lock-in) Measurement Techniques for Magnetic Contrast Enhancement in STXM

    SciTech Connect

    Kaznatcheev, K.; Bertwistle, D.; Cheng, C.; Zohar, S.; Bailey, W. E.

    2011-09-09

    We have explored the capabilities of synchronous ('lock-in') point detection techniques to enhance the x-ray magnetic circular dichroism (XMCD) contrast in scanning x-ray transmission microscopy (STXM) of magnetic thin-film microstructures. Local absorption contrast, measured synchronously with low-amplitude (<10 Oe) and low-frequency (<200 hz) longitudinal fields perturbing the near-remanent magnetization state, reveal a strong spatial dependence of the response, with a roll-off in frequency response above 200 Hz. In this context, synchronous measurement affords us a basis for imaging the relation between energy loss and the sweeping rate. We speculate that the lock-in approach will be uniquely suited for detailing stochastic and deterministic frequency-dependent events in the process of magnetization reversal.

  14. Alternate Methods of Effluent Disposal for On-Lot Home Sewage Systems. Special Circular 214.

    ERIC Educational Resources Information Center

    Wooding, N. Henry

    This circular provides current information for homeowners who must repair or replace existing on-lot sewage disposal systems. Several alternatives such as elevated sand mounds, sand-lined beds and trenches and oversized absorption areas are discussed. Site characteristics and preparation are outlined. Each alternative is accompanied by a diagram…

  15. ABSORPTION ANALYZER

    DOEpatents

    Brooksbank, W.A. Jr.; Leddicotte, G.W.; Strain, J.E.; Hendon, H.H. Jr.

    1961-11-14

    A means was developed for continuously computing and indicating the isotopic assay of a process solution and for automatically controlling the process output of isotope separation equipment to provide a continuous output of the desired isotopic ratio. A counter tube is surrounded with a sample to be analyzed so that the tube is exactly in the center of the sample. A source of fast neutrons is provided and is spaced from the sample. The neutrons from the source are thermalized by causing them to pass through a neutron moderator, and the neutrons are allowed to diffuse radially through the sample to actuate the counter. A reference counter in a known sample of pure solvent is also actuated by the thermal neutrons from the neutron source. The number of neutrons which actuate the detectors is a function of a concentration of the elements in solution and their neutron absorption cross sections. The pulses produced by the detectors responsive to each neu tron passing therethrough are amplified and counted. The respective times required to accumulate a selected number of counts are measured by associated timing devices. The concentration of a particular element in solution may be determined by utilizing the following relation: T2/Ti = BCR, where B is a constant proportional to the absorption cross sections, T2 is the time of count collection for the unknown solution, Ti is the time of count collection for the pure solvent, R is the isotopic ratlo, and C is the molar concentration of the element to be determined. Knowing the slope constant B for any element and when the chemical concentration is known, the isotopic concentration may be readily determined, and conversely when the isotopic ratio is known, the chemical concentrations may be determined. (AEC)

  16. Circular polarization in the optical afterglow of GRB 121024A.

    PubMed

    Wiersema, K; Covino, S; Toma, K; van der Horst, A J; Varela, K; Min, M; Greiner, J; Starling, R L C; Tanvir, N R; Wijers, R A M J; Campana, S; Curran, P A; Fan, Y; Fynbo, J P U; Gorosabel, J; Gomboc, A; Götz, D; Hjorth, J; Jin, Z P; Kobayashi, S; Kouveliotou, C; Mundell, C; O'Brien, P T; Pian, E; Rowlinson, A; Russell, D M; Salvaterra, R; di Serego Alighieri, S; Tagliaferri, G; Vergani, S D; Elliott, J; Fariña, C; Hartoog, O E; Karjalainen, R; Klose, S; Knust, F; Levan, A J; Schady, P; Sudilovsky, V; Willingale, R

    2014-05-01

    Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets.

  17. Spontaneous circular polarization of photoluminescence from WS2 single layers

    NASA Astrophysics Data System (ADS)

    Scrace, Thomas; Tsai, Yutsung; Barman, Biplob; Zhang, Peiyao; Petrou, Athos; Kioseoglou, George; Korkusinski, Marek; Ozfidan, Isil; Hawrylak, Pawel

    2015-03-01

    We have carried out a magnetoluminescence study of WS2 single layer crystals excited with linearly polarized light. The photoluminescence (PL) contains two features. The first is associated with the neutral exciton (X0) ; the second feature is due to the recombination of negatively charged excitons (X-) in the presence of a two-dimensional electron gas (2DEG). The X- - 2 DEG feature has a non-zero circular polarization up to 19% at zero magnetic field even though the PL excitation light is linearly polarized. The circular polarization is effected by an external magnetic field applied perpendicular to the crystal plane at 2 % / Tesla . The zero field circular polarization of the X- - 2 DEG photoluminescence feature is interpreted as due to the existence of a spontaneously valley polarized 2DEG. This is a new state possible in WS2 due to valley and spin locking and a strong electron-electron interaction. Work at SUNY Buffalo has been supported by ONR. I.O., M.K. and P.H. acknowledge support of NRC QPSS program and of NSERC.

  18. Circular polarization in the optical afterglow of GRB 121024A

    NASA Astrophysics Data System (ADS)

    Wiersema, K.; Covino, S.; Toma, K.; van der Horst, A. J.; Varela, K.; Min, M.; Greiner, J.; Starling, R. L. C.; Tanvir, N. R.; Wijers, R. A. M. J.; Campana, S.; Curran, P. A.; Fan, Y.; Fynbo, J. P. U.; Gorosabel, J.; Gomboc, A.; Götz, D.; Hjorth, J.; Jin, Z. P.; Kobayashi, S.; Kouveliotou, C.; Mundell, C.; O'Brien, P. T.; Pian, E.; Rowlinson, A.; Russell, D. M.; Salvaterra, R.; di Serego Alighieri, S.; Tagliaferri, G.; Vergani, S. D.; Elliott, J.; Fariña, C.; Hartoog, O. E.; Karjalainen, R.; Klose, S.; Knust, F.; Levan, A. J.; Schady, P.; Sudilovsky, V.; Willingale, R.

    2014-05-01

    Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets.

  19. Circular polarization in the optical afterglow of GRB 121024A.

    PubMed

    Wiersema, K; Covino, S; Toma, K; van der Horst, A J; Varela, K; Min, M; Greiner, J; Starling, R L C; Tanvir, N R; Wijers, R A M J; Campana, S; Curran, P A; Fan, Y; Fynbo, J P U; Gorosabel, J; Gomboc, A; Götz, D; Hjorth, J; Jin, Z P; Kobayashi, S; Kouveliotou, C; Mundell, C; O'Brien, P T; Pian, E; Rowlinson, A; Russell, D M; Salvaterra, R; di Serego Alighieri, S; Tagliaferri, G; Vergani, S D; Elliott, J; Fariña, C; Hartoog, O E; Karjalainen, R; Klose, S; Knust, F; Levan, A J; Schady, P; Sudilovsky, V; Willingale, R

    2014-05-01

    Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets. PMID:24776800

  20. NON-ZEEMAN CIRCULAR POLARIZATION OF MOLECULAR ROTATIONAL SPECTRAL LINES

    SciTech Connect

    Houde, Martin; Jones, Scott; Rajabi, Fereshte; Hezareh, Talayeh

    2013-02-10

    We present measurements of circular polarization from rotational spectral lines of molecular species in Orion KL, most notably {sup 12}CO (J = 2 {yields} 1), obtained at the Caltech Submillimeter Observatory with the Four-Stokes-Parameter Spectral Line Polarimeter. We find levels of polarization of up to 1%-2% in general; for {sup 12}CO (J = 2 {yields} 1) this level is comparable to that of linear polarization also measured for that line. We present a physical model based on resonant scattering in an attempt to explain our observations. We discuss how slight differences in scattering amplitudes for radiation polarized parallel and perpendicular to the ambient magnetic field, responsible for the alignment of the scattering molecules, can lead to the observed circular polarization. We also show that the effect is proportional to the square of the magnitude of the plane of the sky component of the magnetic field and therefore opens up the possibility of measuring this parameter from circular polarization measurements of Zeeman insensitive molecules.

  1. Ultrafast optical manipulation of magnetic order

    NASA Astrophysics Data System (ADS)

    Kirilyuk, Andrei; Kimel, Alexey V.; Rasing, Theo

    2010-07-01

    The interaction of subpicosecond laser pulses with magnetically ordered materials has developed into a fascinating research topic in modern magnetism. From the discovery of subpicosecond demagnetization over a decade ago to the recent demonstration of magnetization reversal by a single 40fs laser pulse, the manipulation of magnetic order by ultrashort laser pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation, and quantum computation. Understanding the underlying mechanisms implies understanding the interaction of photons with charges, spins, and lattice, and the angular momentum transfer between them. This paper will review the progress in this field of laser manipulation of magnetic order in a systematic way. Starting with a historical introduction, the interaction of light with magnetically ordered matter is discussed. By investigating metals, semiconductors, and dielectrics, the roles of (nearly) free electrons, charge redistributions, and spin-orbit and spin-lattice interactions can partly be separated, and effects due to heating can be distinguished from those that are not. It will be shown that there is a fundamental distinction between processes that involve the actual absorption of photons and those that do not. It turns out that for the latter, the polarization of light plays an essential role in the manipulation of the magnetic moments at the femtosecond time scale. Thus, circularly and linearly polarized pulses are shown to act as strong transient magnetic field pulses originating from the nonabsorptive inverse Faraday and inverse Cotton-Mouton effects, respectively. The recent progress in the understanding of magneto-optical effects on the femtosecond time scale together with the mentioned inverse, optomagnetic effects promises a bright future for this field of ultrafast optical manipulation of magnetic order or femtomagnetism.

  2. Explosive Chromospheric Evaporation in a Circular-ribbon Flare

    NASA Astrophysics Data System (ADS)

    Zhang, Q. M.; Li, D.; Ning, Z. J.; Su, Y. N.; Ji, H. S.; Guo, Y.

    2016-08-01

    In this paper, we report our multiwavelength observations of the C4.2 circular-ribbon flare in active region (AR) 12434 on 2015 October 16. The short-lived flare was associated with positive magnetic polarities and a negative polarity inside, as revealed by the photospheric line-of-sight magnetograms. Such a magnetic pattern is strongly indicative of a magnetic null point and spine-fan configuration in the corona. The flare was triggered by the eruption of a mini-filament residing in the AR, which produced the inner flare ribbon (IFR) and the southern part of a closed circular flare ribbon (CFR). When the eruptive filament reached the null point, it triggered null point magnetic reconnection with the ambient open field and generated the bright CFR and a blowout jet. Raster observations of the Interface Region Imaging Spectrograph show plasma upflow at speeds of 35-120 km s-1 in the Fe xxi λ1354.09 line ({log}T≈ 7.05) and downflow at speeds of 10-60 km s-1 in the Si iv λ1393.77 line ({log}T≈ 4.8) at certain locations of the CFR and IFR during the impulsive phase of the flare, indicating explosive chromospheric evaporation. Coincidence of the single hard X-ray source at 12-25 keV with the IFR and calculation based on the thick-target model suggest that the explosive evaporation was most probably driven by nonthermal electrons.

  3. Preparation of magnetic metal organic frameworks adsorbent modified with mercapto groups for the extraction and analysis of lead in food samples by flame atomic absorption spectrometry.

    PubMed

    Wang, Yang; Chen, Huanhuan; Tang, Jie; Ye, Guiqin; Ge, Huali; Hu, Xiaoya

    2015-08-15

    A novel magnetic metal organic frameworks adsorbent modified with mercapto groups was synthesized and developed for extraction and spectrophotometric determination of trace lead. The adsorbent was characterized by Fourier transforms infrared spectrometer, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. The results indicated the adsorbents exhibited high adsorption capacities for lead due to the chelation mechanism between metal cations and mercapto groups. Meanwhile, the lead sorption onto the adsorbents could be easily separated from aqueous solution using a magnetic separation method. Under the optimal conditions, a linear calibration curve in the range from 1 to 20 μg L(-1) was achieved with an enrichment factor of 100. The limits of detection and quantitation for lead were found to be 0.29 and 0.97 μg L(-1), respectively. The developed method was successfully applied to the determination of trace amounts of lead in food samples and certified reference material with satisfactory results. PMID:25794739

  4. Preparation of magnetic metal organic frameworks adsorbent modified with mercapto groups for the extraction and analysis of lead in food samples by flame atomic absorption spectrometry.

    PubMed

    Wang, Yang; Chen, Huanhuan; Tang, Jie; Ye, Guiqin; Ge, Huali; Hu, Xiaoya

    2015-08-15

    A novel magnetic metal organic frameworks adsorbent modified with mercapto groups was synthesized and developed for extraction and spectrophotometric determination of trace lead. The adsorbent was characterized by Fourier transforms infrared spectrometer, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. The results indicated the adsorbents exhibited high adsorption capacities for lead due to the chelation mechanism between metal cations and mercapto groups. Meanwhile, the lead sorption onto the adsorbents could be easily separated from aqueous solution using a magnetic separation method. Under the optimal conditions, a linear calibration curve in the range from 1 to 20 μg L(-1) was achieved with an enrichment factor of 100. The limits of detection and quantitation for lead were found to be 0.29 and 0.97 μg L(-1), respectively. The developed method was successfully applied to the determination of trace amounts of lead in food samples and certified reference material with satisfactory results.

  5. Robust, angstrom level circularity profilometry

    NASA Technical Reports Server (NTRS)

    Glenn, Paul

    1990-01-01

    A noncontacting approach is presented which involves measuring the local circumferential curvature of the test piece by simultaneously measuring its circumferential slope at two slightly displaced locations. A pair of sensing beams is scanned along the circumference, and a profile of curvature is built, from which the circularity profile is deduced. The sensing of curvature makes the approach insensitive to all types of vibration and drift and runout errors in the relative rotation. The special qualities of the approach are summarized which make it well suited to measuring cylindrical optics and enable it to accommodate radii as small as twenty millimeters.

  6. Manipulating photoinduced voltage in metasurface with circularly polarized light.

    PubMed

    Bai, Qiang

    2015-02-23

    Recently, the concept of metasurface has provided one an unprecedented opportunity and ability to control the light in the deep subwavelength scale. However, so far most efforts are devoted to exploiting the novel scattering properties and applications of metasurface in optics. Here, I theoretically and numerically demonstrate that longitudinal and transverse photoinduced voltages can be simultaneously realized in the proposed metasurface utilizing the magnetic resonance under the normal incidence of circularly polarized light, which may extend the concept and functionality of metasurface into the electronics and may provide a potential scheme to realize a nanoscale tunable voltage source through a nanophotonic roadmap. The signs of longitudinal and transverse photoin-duced voltages can be manipulated by tuning the resonant frequency and the handedness of circularly polarized light, respectively. Analytical formulae of photoinduced voltage are presented based on the theory of symmetry of field. This work may bridge nanophotonics and electronics, expands the capability of metasurface and has many potential applications. PMID:25836566

  7. Impact of energy-related pollutants on chromosome structure. Progress report, January 1-December 31, 1980. IQUID COLUMN CHROMATOGRAPHY; ABSORPTION SPECTRA; COMPUTER CODES; DICHROISM; EQUIPMENT INTERFACES; MICROPROCESSORS; SPECTROPHOTOMETERS; ; CARBON 13; COMPLEXES; NUCLEAR MAGNETIC RESONANCE

    SciTech Connect

    Not Available

    1980-01-01

    Methods for rapidly analyzing methylated and ethylated nucleosides and bases by high pressure liquid chromatography were investigated. Deoxyribonucleotides were alkylated with alkyl iodides and dialkyl sulfates. Several unreported products of the reactions of methyl and ethyl iodide in dimethylsulfoxide were found and are being characterized. The Cary 219 UV-Vis spectrophotometer was interfaced to a microcomputer and several utility programs were written. Preliminary absorption and circular dichroism studies of the binding of ethidium to DNA and nucleosome cores showed binding to cores to be quite different from binding to DNA. Free radical and additional reactions of bisulfite with DNA in chromatin were examined. Free radical attack was minimal. Some conversion of cytosine to uracil was noted, but protein crosslinking to DNA was not detected. The first valid natural abundance /sup 13/C nmr spectra of double-stranded DNA and double-stranded DNA complexed with ethidium were obtained. These spectra suggested that DNA undergoes considerable internal motion. The data show that 13-C nmr studies of the conformational and motional properties of native DNA and of complexes of native DNA with small molecules are practical and promising. Studies of subnucleosomes derived from nucleosomes were completed. Based on these studies, a model of the linear arrangement of histone C-terminal and N-terminal chain regions along nucleosome DNA was proposed. The use of staphylococcal protease to probe histone conformations in nucleosomes was explored. Preliminary data indicate that H3 is much more susceptible to protease than other core histones, and is cleaved in its hydrophobic domain. A procedure for fractionating chromatin was alos developed. (ERB)

  8. Interface effect of magnetic properties in Ni nanoparticles with a hcp core and fcc shell structure.

    PubMed

    Choo, Seongmin; Lee, Kyujoon; Jo, Younghun; Yoon, Seon-Mi; Choi, Jae-Young; Kim, Jea-Young; Park, Jea-Hoon; Lee, Kyung-Jin; Lee, Jong-Heun; Jung, Myung-Hwa

    2011-07-01

    We have fabricated hexagonal close-packed (hcp) Ni nanoparticles covered by a face-centered cubic (fcc) Ni surface layer by polyol method. The magnetic properties have been investigated as a function of temperature and applied magnetic field. The magnetic behavior reveals that the system should be divided magnetically into three distinct phases with different origins. The fcc Ni phase on the shell contributes to the superparamagnetism through a wide temperature range up to 360 K. The hcp Ni phase at the core is associated with antiferromagnetic nature below 12 K. These observations are in good agreement with the X-ray absorption spectroscopy and magnetic circular dichroism measurements. In our particular case, the unique hcp core and fcc shell structure gives rise to an additional anomaly at 20 K in the zero-field-cooled magnetization curve. Its position is barely affected by the magnetic field but its structure disappears above 30 kOe, showing a metamagnetic transition in the magnetization versus magnetic field curve. This new phase originates from the magnetic exchange at the interface between the hcp and fcc Ni sublattices.

  9. Combined use of lightweight magnetic Fe3O4-coated hollow glass spheres and electrically conductive reduced graphene oxide in an epoxy matrix for microwave absorption

    NASA Astrophysics Data System (ADS)

    Wang, Junpeng; Wang, Jun; Zhang, Bin; Sun, Yu; Chen, Wei; Wang, Tao

    2016-03-01

    Epoxy resin based lightweight composites comprising Fe3O4-coated hollow glass spheres (HGS@Fe3O4) and reduced graphene oxide (RGO) were prepared. Impedance matching condition and electromagnetic wave attenuation characteristic are used for analysis of the reflection loss (RL) performance of the composites. Compared with pure HGS@Fe3O4 and RGO composite, the -10 dB absorption bandwidth and the minimum RL of the hybrid composites are enhanced. RL values less than -10 dB are obtained in a wide frequency range and the corresponding bandwidth can reach up to 3.6 GHz when an appropriate absorber thickness is chosen. The density of the hybrid composite is in the range of 0.57-0.72 g/cm3, which is attractive candidate for a new type of lightweight microwave absorber.

  10. Role of incoherent pumping field on absorption-dispersion properties of probe pulse in a graphene nanostructure under external magnetic field

    NASA Astrophysics Data System (ADS)

    Asadpour, Seyyed Hossein; Hamedi, H. R.; Soleimani, H. Rahimpour

    2015-07-01

    The optical properties of weak probe light based on quantum coherence and interference in Landau-quantized graphene nanostructure driven by two coherent fields and incoherent pumping field is investigated. The linear dynamical properties of the graphene by means of density matrix method and perturbation theory are discussed. It is found that under certain condition and for appropriate choosing the parameters of the medium, the absorption, dispersion, group index of the weak probe light can be controlled. Moreover, it is shown that by means of incoherent pumping field the superluminal light propagation in the system is accompanied by amplification to make sure that the probe field is amplified as it passes through the system. Moreover, it is observed that the probe amplification can be obtained in the presence or absence of population inversion by properly choosing of system's parameters. We hope that these results may have useful in the future quantum communicational system and networks.

  11. Physics at Future Circular Colliders

    NASA Astrophysics Data System (ADS)

    Kotwal, Ashutosh

    2016-03-01

    The Large Hadron Collider has been a grand success with the discovery of the Higgs boson, with bright prospects for additional discoveries since the recent increase in collider energy and the anticipated large datasets. Big open questions such as the nature of dark matter, the origin of the matter-antimatter asymmetry in the Universe, and the theoretical puzzle of the finely-tuned parameters in the Higgs sector, demand new physics principles that extend the established Standard Model paradigm. Future circular colliders in a substantially larger tunnel can house both a high luminosity electron-positron collider for precision measurements of Higgs and electroweak parameters, as well as a very high energy proton-proton collider which can directly manifest particles associated with these new physics principles. We discuss the physics goals of these future circular colliders, and the prospects for elucidating fundamental new laws of nature that will significantly extend our understanding of the Universe. Detailed studies of the discovery potential in specific benchmark models will be presented, with implications for detector design.

  12. Total positive curvature of circular DNA.

    PubMed

    Bohr, Jakob; Olsen, Kasper W

    2013-11-01

    The properties of double-stranded DNA and other chiral molecules depend on the local geometry, i.e., on curvature and torsion, yet the paths of closed chain molecules are globally restricted by topology. When both of these characteristics are to be incorporated in the description of circular chain molecules, e.g., plasmids, it is shown to have implications for the total positive curvature integral. For small circular micro-DNAs it follows as a consequence of Fenchel's inequality that there must exist a minimum length for the circular plasmids to be double stranded. It also follows that all circular micro-DNAs longer than the minimum length must be concave, a result that is consistent with typical atomic force microscopy images of plasmids. Predictions for the total positive curvature of circular micro-DNAs are given as a function of length, and comparisons with circular DNAs from the literature are presented.

  13. Total positive curvature of circular DNA

    NASA Astrophysics Data System (ADS)

    Bohr, Jakob; Olsen, Kasper W.

    2013-11-01

    The properties of double-stranded DNA and other chiral molecules depend on the local geometry, i.e., on curvature and torsion, yet the paths of closed chain molecules are globally restricted by topology. When both of these characteristics are to be incorporated in the description of circular chain molecules, e.g., plasmids, it is shown to have implications for the total positive curvature integral. For small circular micro-DNAs it follows as a consequence of Fenchel's inequality that there must exist a minimum length for the circular plasmids to be double stranded. It also follows that all circular micro-DNAs longer than the minimum length must be concave, a result that is consistent with typical atomic force microscopy images of plasmids. Predictions for the total positive curvature of circular micro-DNAs are given as a function of length, and comparisons with circular DNAs from the literature are presented.

  14. Radially uniform circular sweep of ion beam

    SciTech Connect

    Akhmetov, T.D.; Davydenko, V.I.; Ivanov, A.A.; Kobets, V.V.; Medvedko, A.S.; Skorobogatov, D.N.; Tiunov, M.A.

    2006-03-15

    A spiral sweep of the ion beam was suggested to provide sufficiently uniform irradiation of a circular target. It is shown that if the beam radius is small enough, the radius of the beam center should increase as a square root of time to provide uniform radial irradiation of the target. In the complex for Boron Neutron Capture Therapy developed at the Budker Institute of Nuclear Physics, the proton beam sweep will be performed by a sweeper with uniform magnetic field with strength up to 500 G and axial length {approx}20 cm, rotating at 100-2000 Hz, and scanning over the radius at a 1-10 Hz frequency. The sweeper field is produced by four longitudinal flat current windings placed near the inner walls of a box-shaped yoke with the inner opening of a square cross section. A similar sweeping technique can be used in a 200 keV oxygen implanter, which is also under development at the Budker Institute.

  15. Preparation and characterization of magnetic nanoparticles for the on-line determination of gold, palladium, and platinum in mine samples based on flow injection micro-column preconcentration coupled with graphite furnace atomic absorption spectrometry.

    PubMed

    Ye, Juanjuan; Liu, Shuxia; Tian, Miaomiao; Li, Wanjun; Hu, Bin; Zhou, Weihong; Jia, Qiong

    2014-01-01

    A simple and highly selective procedure for on-line determination of trace levels of Au, Pd, and Pt in mine samples has been developed using flow injection-column adsorption preconcentration coupled with graphite furnace atomic absorption spectrophotometry (FI-column-GFAAS). The precious metals were adsorbed on the as-synthesized magnetic nanoparticles functionalized with 4'-aminobenzo-15-crown-5-ether packed into a micro-column and then eluted with 2% thiourea + 0.1 mol L(-1) HCl solution prior to the determination by GFAAS. The properties of the magnetic adsorbents were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). Various experimental parameters affecting the preconcentration of Au, Pd, and Pt were investigated and optimized. Under the optimal experimental conditions, the detection limits of the developed technique were 0.16 ng mL(-1) for Au, 0.28 ng mL(-1) for Pd, and 1.01 ng mL(-1) for Pt, with enrichment factors of 24.3, 13.9, and 17.8, respectively. Precisions, evaluated as repeatability of results, were 1.1%, 3.9%, and 4.4% respectively for Au, Pd, and Pt. The developed method was validated by the analysis of Au, Pd, and Pt in certified reference materials and mine samples with satisfactory results.

  16. Circular permutant GFP insertion folding reporters

    DOEpatents

    Waldo, Geoffrey S.; Cabantous, Stephanie

    2008-06-24

    Provided are methods of assaying and improving protein folding using circular permutants of fluorescent proteins, including circular permutants of GFP variants and combinations thereof. The invention further provides various nucleic acid molecules and vectors incorporating such nucleic acid molecules, comprising polynucleotides encoding fluorescent protein circular permutants derived from superfolder GFP, which polynucleotides include an internal cloning site into which a heterologous polynucleotide may be inserted in-frame with the circular permutant coding sequence, and which when expressed are capable of reporting on the degree to which a polypeptide encoded by such an inserted heterologous polynucleotide is correctly folded by correlation with the degree of fluorescence exhibited.

  17. Circular permutant GFP insertion folding reporters

    SciTech Connect

    Waldo, Geoffrey S.; Cabantous, Stephanie

    2013-04-16

    Provided are methods of assaying and improving protein folding using circular permutants of fluorescent proteins, including circular permutants of GFP variants and combinations thereof. The invention further provides various nucleic acid molecules and vectors incorporating such nucleic acid molecules, comprising polynucleotides encoding fluorescent protein circular permutants derived from superfolder GFP, which polynucleotides include an internal cloning site into which a heterologous polynucleotide may be inserted in-frame with the circular permutant coding sequence, and which when expressed are capable of reporting on the degree to which a polypeptide encoded by such an inserted heterologous polynucleotide is correctly folded by correlation with the degree of fluorescence exhibited.

  18. Circular permutant GFP insertion folding reporters

    SciTech Connect

    Waldo, Geoffrey S; Cabantous, Stephanie

    2013-02-12

    Provided are methods of assaying and improving protein folding using circular permutants of fluorescent proteins, including circular permutants of GFP variants and combinations thereof. The invention further provides various nucleic acid molecules and vectors incorporating such nucleic acid molecules, comprising polynucleotides encoding fluorescent protein circular permutants derived from superfolder GFP, which polynucleotides include an internal cloning site into which a heterologous polynucleotide may be inserted in-frame with the circular permutant coding sequence, and which when expressed are capable of reporting on the degree to which a polypeptide encoded by such an inserted heterologous polynucleotide is correctly folded by correlation with the degree of fluorescence exhibited.

  19. Circular permutant GFP insertion folding reporters

    SciTech Connect

    Waldo, Geoffrey S.; Cabantous, Stephanie

    2011-06-14

    Provided are methods of assaying and improving protein folding using circular permutants of fluorescent proteins, including circular permutants of GFP variants and combinations thereof. The invention further provides various nucleic acid molecules and vectors incorporating such nucleic acid molecules, comprising polynucleotides encoding fluorescent protein circular permutants derived from superfolder GFP, which polynucleotides include an internal cloning site into which a heterologous polynucleotide may be inserted in-frame with the circular permutant coding sequence, and which when expressed are capable of reporting on the degree to which a polypeptide encoded by such an inserted heterologous polynucleotide is correctly folded by correlation with the degree of fluorescence exhibited.

  20. Polarized Synchrotron Emissivities and Absorptivities for Relativistic Thermal, Power-law, and Kappa Distribution Functions

    NASA Astrophysics Data System (ADS)

    Pandya, Alex; Zhang, Zhaowei; Chandra, Mani; Gammie, Charles F.

    2016-05-01

    Synchrotron emission and absorption determine the observational appearances of many astronomical systems. In this paper, we describe a numerical scheme for calculating synchrotron emissivities and absorptivities in all four Stokes parameters for arbitrary gyrotropic electron distribution functions, building on earlier work by Leung, Gammie, and Noble. We use this technique to evaluate the emissivities and the absorptivities for a thermal (Maxwell-Jüttner), isotropic power-law, and an isotropic kappa distribution function. The latter contains a power-law tail at high particle energies that smoothly merges with a thermal core at low energies, as is characteristic of observed particle spectra in collisionless plasmas. We provide fitting formulae and error bounds on the fitting formulae for use in codes that solve the radiative transfer equation. The numerical method and the fitting formulae are implemented in a compact C library called symphony. We find that the kappa distribution has a source function that is indistinguishable from a thermal spectrum at low frequency and transitions to the characteristic self-absorbed synchrotron spectrum, \\propto {ν }5/2, at high frequency; the linear polarization fraction for a thermal spectrum is near unity at high frequency; and all distributions produce O(10%) circular polarization at low frequency for lines of sight sufficiently close to the magnetic field vector.