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  • 1
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    German Medical Science GMS Publishing House; Düsseldorf
    In:  128. Kongress der Deutschen Gesellschaft für Chirurgie; 20110503-20110506; München; DOC11dgch320 /20110520/
    Publication Date: 2011-05-20
    Keywords: ddc: 610
    Language: German
    Type: conferenceObject
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  • 2
    ISSN: 1432-0630
    Keywords: 75.70Ak ; 73.60Aq ; 75.30Pd ; 79.60Cn
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The thickness dependence of the magnetic band structure of ultrathin, epitaxial Ni(111)/W(110) layers has been studied by spin and angle-resolved photoemission spectroscopy. The changes of the spin-resolved photoemission intensities upon reducing the layer thickness depend strongly on the wavevector along the Γ-L line of the Brillouin zone. The measured exchange splittingΔ atk ≃1/3(Γ-L) andk ≃1/2(Γ-L) is found to be independent of the layer thickness for layers consisting of 3 or more atomic layers, whileΔ decreases rapidly with the layer thickness atk≃2/3(Γ-L). This behavior is very similar to the temperature dependence of the spin-resolved photoemission spectra of bulk Ni(111) at the samek-points.
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  • 3
    ISSN: 1432-0630
    Keywords: 75.30.Ds ; 75.70.-i ; 75.50.Rr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We give an overview on our experimental and theoretical investigations of Brillouin light scattering in magnetic thin films, layered magnetic structures and superlattices. For epitaxial Fe(1 10) layers on W(1 10) the in-plane and out-of-plane magnetic surface anisotropy constants are determined, and the influence of Pd overlayers on the surface anisotropies is studied. For Fe/Pd superlattices a magnetic polarization of the Pd at the interfaces is established and the interface anisotropy constant is determined. For “second order” Fe/Pd superlattices, formed by alternating two Fe/Pd bilayers with different repeat periods, the Brillouin spectrum is obtained and compared to calculations. In the case of magnetic/nonmagnetic multilayered structures we investigate theoretically the crossing regime between dipolar and exchange-dominated modes. For small spacer-layer thicknesses, interlayer exchange coupling shifts the spin-wave frequencies of all but the highest-frequency dipolar mode into the exchange-mode regime. In case of all-magnetic multilayered structures, such as Fe/Ni multilayers, a new type of propagating collective excitations arising from coupled exchange modes is predicted.
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  • 4
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Zusammenfassung Die optischen Konstanten der Eu-Chalkogenide wurden an Einkristallen bei Zimmertemperatur für Photonenergien von 1 bis 6 eV bestimmt. Im gleichen Energiebereich wurde die Transmission von dünnen Aufdampfschichten (ausgenommen EuO) mit polarisiertem Licht oberhalb und unterhalb der magnetischen Ordnungstemperatur gemessen. Die beobachteten polarisationsabhängigen Aufspaltungen der zwei Hauptabsorptionsmaxima im Gebiet der magnetischen Ordnung deuten auf Übergänge vom 4f7-Niveau in die vom Kristallfeld aufgespaltenen 5dt2g- und 5deg-Zustände hin. Ein Versuch wurde unternommen, die Maxima des Absorptionskoeffizienten bestimmten Interbandübergängen und Übergängen von den lokalisierten 4f-Zuständen zuzuordnen und ein konsistentes Energieniveauschema der vier Eu-Chalkogenide aufzustellen. Dieses Schema gibt wertvolle Information über die Breite der 5d-Zustände, die Kristallfeldaufspaltung und den möglichen Leitfähigkeitscharakter. Schließlich haben wir versucht, die experimentell im Gebiet der magnetischen Ordnung beobachteten Aufspaltungen theoretisch zu erklären. Ein Einteilchen-Modell wurde verwendet, um die Übergangswahrscheinlichkeiten für die 4f7−4f6(7F J ) 5dt2g- und 4f7−4f6(7F J ) 5deg-Übergänge zu berechnen unter Berücksichtigung sowohl einer Austausch-Wechselwirkung als auch einer Spin-Bahn-Kopplung. Obgleich dieses einfache Modell die Aufspaltungen des angeregten Zustandes 4f6(7F J ) 5deg erklären kann, scheiterte bisher eine vollständige Erklärung des Einflusses der magnetischen Ordnung auf den 4f6(7F J ) 5dt2g-Zustand.
    Abstract: Résumé Les constantes optiques de monocristaux des chalcogénures d'europium ont été déterminées à la température ambiante pour des énergies de 1 à 6 eV. La transmission de couches minces (à l'exception de EuO) a été mesurée avec de la lumière polarisée pour les mêmes énergies au-dessus et au-dessous de leurs température d'ordre magnétique. Dans la région d'ordre magnétique les décompositions, dépendantes de la polarisation, des deux maxima d'absorption principaux sugèrent des transitions du niveau 4f7 dans les états 5dt2g et 5deg, décomposés par le champ cristallin. Nous avons essayé de correler les maxima du coefficient d'absorption avec des transitions entre bandes et des transitions des états 4f localisés et de déduire un schéma des niveaux d'énergie des quatre chalcogénures d'europium. Ce schéma permet une évaluation de la largeur des états 5d, de la décomposition par le champ cristallin et du charactère possible de la conductibilité. Enfin nous avons tenté de donner une explication théorique pour les décompositions observées expérimentallement dans la région d'ordre magnétique. A cette fin nous avons utilisé pour calculer les probabilités de transition des transitions 4f7−4f6(7F J ) 5dt2g et 4f7−4f6(7F J ) 5deg un modèle à une particle en tenant compte d'une interaction d'échange et d'un couplage spin-orbite. Bien que ce modèle très simple puisse expliquer la décomposition de l'état excité 4f6(7F J ) 5deg, il ne permet pas une explication complète de l'effet d'ordre magnétique à l'état 4f6(7F J ) 5dt2g.
    Notes: Abstract The optical constants of Eu-chalcogenide single crystals have been determined at room temperature for photon energies from 1 to 6 eV. In the same energy range the transmission of thin evaporated films (except for EuO) has been measured with polarized light above and below the magnetic ordering temperature. The observed polarization-dependent splittings of the two main absorption maxima in the region of magnetic order suggest transitions from the 4f7-level into the crystal field split 5dt2g- and 5deg-states. An attempt has been made to relate the maxima of the absorption coefficient to interband transitions and transitions from the localized 4f-states. With this assumption we derived a consistent energy level scheme of the four Eu-chalcogenides. From the scheme we gained useful information about the width of the 5d-states, the crystal field splitting and the possible type of conductivity. Finally we tried to explain theoretically the splittings observed in the region of magnetic order. For this purpose a one-particle model has been used to calculate the transition probabilities for the 4f7−4f6(7F J ) 5dt2g and the 4f7−4f6(7F J ) 5deg transition, taking into account an exchange interaction as well as a spin-orbit coupling. Although this simple model can explain the splittings of the excited 4f6(7F J ) 5deg-state, a complete explanation of the effect of magnetic order on the 4f6(7F J ) 5dt2g-state fails up to now.
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  • 5
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Elastic constants of CeB6 were redetermined by ultrasonic and Brillouin scattering measurements. We found all elastic constants to be positive, especiallyc 12. The temperature and magnetic field dependence of the elastic modesc 44 and (c 11-c 12)/2 is explained on the basis of the newly proposed crystalline-electric-field level scheme for CeB6 with theΓ 7 level 545 K above theΓ 8 ground state. The deduced quadrupolar coupling constants give an antiferroquadrupolar ordering temperature of 3.3 K in agreement with experiment.
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  • 6
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent progress of light scattering in metals is reviewed by selected highlights: Raman scattering in CeB6 has established a new crystalline electric field (CEF) level scheme with aΓ 8 ground state. The resonant CEF-phonon coupling has been identified in CeAl2. The ionic model description of intermediate valence of rare earth (RE) ions in metals could directly be proved by Raman spectroscopy in EuPd2Si2. Brillouin scattering from elastic surface wave excitations of bulk metals or supported thin layers can now be used for the reliable determination of their elastic constants. For very thin metallic layers light scattering has been very successful in observing the dispersion of standing spin waves and their elastic analogue, the Sezawa waves. From the standing spin waves the exchange constant can be determined most directly. The investigation of Au clusters deposited on NaCl has revealed a new localized acoustic surface mode (“cluster mode”). Its frequency crosses with increasing Au deposition the frequency of the transverse acoustic phonon mode of the substrate at the percolation threshold.
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  • 7
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have determined the crystalline-electric-field (CEF) level scheme of NdB6 by means of Raman spectroscopy. We could resolve two CEF-transitions at 92 cm−1 and 98 cm−1 due to the spectral resolution of 2 cm−1 (=0.25 meV). The temperature dependent Raman scattering reveals the two transitions to be on top of one another, in agreement with fits of the temperature dependence of the magnetic susceptibility. The spectroscopically determined CEF level scheme yields a good fit of the elastic constants and hence the mean field prediction of a ferroquadrupolar ordering near 6 K. This result sheds new light on the phase transition in NdB6 nearT N =8.6 K which has so far been interpreted only in terms of antiferromagnetic ordering.
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  • 8
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Brillouin spectroscopy of the heavy fermion metal UPt3 shows strong quasielastic scattering, which has no analogue in ordinary metals. An enhanced Landau-Placzek ratio relating the quasielastic to the inelastic scattering intensity is deduced from the line shape analysis. The quasielastic line is of nonmagnetic origin and is attributed to electron density fluctuations as predicted by a recent theory of hydrodynamic fluctuations in heavy fermion systems.
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  • 9
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Tunneling and point-contact measurements have been performed on different high-T c superconductors M−Ba2Cu3O7 with M=Y, La, Eu. The average energy gaps deduced from the tunneling spectra are about 2Δ=33 meV for the Y- and La-type samples and about 2Δ=38 meV for the Eu-type samples, which give ratios 2Δ/k B T c in the range from 4 to 6. The point-contact characteristics show a distinct minimum in the differential resistance about zero bias and additional sharp spikes up to 40 mV. From these pointcontacts we can give an estimate of the critical current, yielding values in the range from 0.2 to 3 mA.
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  • 10
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Polycrystalline Bi-2212 or Bi-2223 systems and single crystals of the Bi-2212 system were investigated at several temperatures by means of the break-junction and point-contact tunneling techniques, respectively. In the case of Bi-2223 we obtained an averaged gap value 2Δ=65±4 meV. The Bi-2212 system yields 2Δ= 45±5 meV in the case of polycrystalline samples and 2Δ=47±5 meV in the case of single crystals. Hence there result BCS-ratios 2Δ/k B T c of 7.3, 6.8 and 6.5, respectively. A dc-Josephson-type supercurrent could be observed in polycrystalline Bi-2212 samples in addition to the usual gap structure. The point-contact tunneling spectra of Bi-2212 single crystals exhibit structures in the second derivative d2 I/d V 2 which we interpret as inelastic tunneling processes due to electron-phonon scattering most likely in the barrier region. The phonon energies deduced from these structures are in accordance with data obtained from inelastic neutron scattering and Raman spectroscopy. Good agreement is obtained with a lattice dynamical calculation of the partial phonon densities of states of individual atoms in the unit cell.
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