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  • 1985-1989  (9)
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  • 1
    Electronic Resource
    Electronic Resource
    Sublattice magnetization and spin reorientation in Nd2Fe14B (abstract) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3728-3728 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Considerable efforts have recently been made in understanding the magnetic behavior of the rare-earth transition-metal compound Nd2Fe14B, which orders ferromagnetically at Tc=600 K and exhibits a spin-reorientation transition at TSR=135 K. In an effort to obtain direct information on the spin configuration and magnetic ordering in this technologically important compound, we have performed a Nd-145 Mössbauer study on a single crystal of Nd2Fe14B using the 72.5-keV nuclear gamma resonance of Nd-145. The results clearly show that the temperature dependence of the Nd-sublattice magnetization is totally different from that of the macroscopic magnetization, i.e., dropping off far below Tc. The results suggest that the spin-reorientation transition in Nd2Fe14B is driven by an ordering of the Nd sublattice below TSR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340649
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  • 2
    Electronic Resource
    Electronic Resource
    Increase of T c in YBa 2 Cu 3 O 7–δ by exposure to nitrogen (1987)
    [s.l.] : Nature Publishing Group
    Nature 330 (1987), S. 213-214 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR-Recently, Matthews et a/.' have reported an increase in the superconducting transition temperature (7^) of YBa^Cu^O^ by as much as 40 K when using nitrogen as a heat exchange medium. In view of the surprising results, and of the fact that this area is riddled with irreproducibilities, we have ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/330213c0
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Interface formation of Bi-based high-T c superconductors with Mg and Ag (1989)
    Springer
    The European physical journal 74 (1989), S. 191-195 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The results of a photoemission study using synchrotron radiation concerning the structure of interfaces between Bi5Sr3Ca2Cu4Oy and the metals Mg and Ag are reported. Interfaces formed with Mg are found to be highly reactive. Oxygen is removed from the interfacial region by oxidation of the Mg overlayer leading to a reduction of Bi and Cu ions and in this way inducing a metal-to-semiconductor transition in the substrate layers adjacent to the interface. On the other hand, interfaces with Ag are found to be essentially non-reactive. Even at coverages up to 25 Å, a Ag film deposited on a ceramic pellet is found to be non-continuous, rendering Ag coating an unsuitable means for passivating Bi5Sr3Ca2Cu4Oy in form of ceramic pellets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307385
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  • 4
    Electronic Resource
    Electronic Resource
    Eu valency and recoil-free fraction in EuCo2Si2-x Ge x (1989)
    Springer
    The European physical journal 73 (1989), S. 511-517 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The valency of Eu in EuCo2Si2-x Ge x withx=0, 0.5, 1.0, and 2 was determined by151Eu-Mössbauer, Eu-L III X-ray absorption as well as magnetization studies in the temperature range from 4.1 to 650 K and at external pressures up to 66 kbar. Eu in EuCo2Si2 is found to be predominantly trivalent, while in EuCo2Ge2 it is divalent. In EuCo2Si2-x Ge x (0≦x≦2), two separate narrow Mössbauer absorption lines are observed, corresponding to stable divalent and trivalent Eu ions. In EuCo2Si1.5Ge0.5, the relative spectral areas of the Eu2+ and Eu3+ Mössbauer lines are found to be strongly temperature and pressure dependent. A decrease in temperature or an application of pressure leads to small changes in the positions of the two absorption lines and to a pronounced increase in the relative spectral area of the Eu2+ component. On the other hand, X-ray absorption near-edge structure (XANES) measurements at theL III threshold of Eu reveal no change in the relative intensity of the Eu2+ and Eu3+ subspectra as a function of temperature. From these observations it is concluded that the recoil-free fractions of the Eu2+ and Eu3+ Mössbauer resonances in EuCo2Si1.5Ge0.5 depend in a substantially different way on temperature. With the Debye approximation, Debye temperatures of θD(Eu2+)=175 K and ΘD(Eu3+)=250 K are derived. These results clearly show that relative abundances of Eu2+ and Eu3+ ions may only be derived from Mössbauer linie intensities, if appropriate corrections for differences in recoil-free fraction are applied; this applies even to mixed-valent systems, where Eu ions with different valencies occupy crystallographically equivalent sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01319380
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  • 5
    Electronic Resource
    Electronic Resource
    Photoemission study of alkali/GaAs(110) interfaces (1989)
    Springer
    The European physical journal 74 (1989), S. 21-33 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A detailed core-level photoemission study of interfaces between thin alkali films andn-orp-type GaAs (110) formed at different substrate temperatures 85 K and 300 K) is reported. All the interfaces grown at 85 K (with Na, K, Rb, and Cs) were found to be non-reactive, while at 300 K, the interface with Na is reactive and that with Cs remains non-reactive. In case of the non-reactive interfaces, a strong band bending of ≊1.0 eV is observed forp-GaAs at alkali coverages as low as θ≊0.01 monolayers, but practically none forn-GaAs. This striking asymmetry in band bending is interpreted as a consequence of the donor character of the alkali atoms. On the other hand, an approximately symmetric band bending at low coverages is observed for the reactive interfaces of Na withn- andp-GaAs and assigned to defect states. For high alkali coverages (θ〉2 monolayers), the final band bending is characterizeds by the same Fermilevel position forn- andp-GaAs, independent of the reactivity of the interface, and assigned to metal-induced gap states. Furthermore, systematic trends along the alkali series in Fermi-level position ionization energy, plasmon-loss features, and layer-dependent binding-energy shifts of alkali core levels are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307236
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  • 6
    Electronic Resource
    Electronic Resource
    High resolution photoabsorption spectroscopy at the carbonK-Edge (1989)
    Springer
    Applied physics 49 (1989), S. 393-397 
    Details
    ISSN: 1432-0630
    Keywords: 07.85.+n ; 33.20.Rm ; 35.20.Pa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Using plane grating, ellipsoidal mirror, grazing incidence monochromators at the storage ring BESSY, a resolution of ≦ 150meV was achieved for a photon energy of 285 eV. This high energy resolution considerably extends the range of possible studies using core level Spectroscopy. Some of the new opportunities are illustrated at the CK edge by resolving the vibrational fine structure of condensed C2H4 multilayers in the (1s−1, π*) state by means of photoabsorption spectroscopy. For the sake of comparison with other high resolution instruments, the vibrational fine structure of condensed N2 multilayers at the NK edge (∼ 400eV) was also measured, yielding a resolving power of 3000.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00615022
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  • 7
    Electronic Resource
    Electronic Resource
    Mössbauer studies of YBa2Cu3O7−δ-type high-T c superconductors (1989)
    Springer
    Hyperfine interactions 50 (1989), S. 555-567 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The local magnetic, electronic, and structural properties of (RE)Ba2Cu3O7−δ supercondcutors (RE=Gd, Dy, and Eu) were studied by Mössbauer spectroscopy using the resonances of155Gd,161Dy,151Eu, and57Eu. In GdBa2Cu3O7−δ, different magnetic ordering behaviors of the Gd sublattice are found for the orthorhombic (superconducting) and tetragonal (non-superconducting) phases. In DyBa2Cu3O7−δ, the magnetic moments of the respective CEF ground states in the orthorhombic and tetragonal phases are derived from paramagnetic hyperfine splittings at 1.4 K. In both DyBa2Cu3O7−δ and EuBa2Cu3O7−δ, anomalies connected with the superconducting transitions in isomer shift, recoil-free fraction, and relaxation behavior were looked for, but not found. The electric-quadrupole splittings observed for both systems are discussed in connection with the lattice EFGs derived for the Gd system. In GdBa2 (Cu0.995Fe0.005)3O7−δ, the local properties of the various Fe sites are investigated over a wide temperature range in both the orthorhombic and tetragonal phase. The magnetic ordering of the Gd sublattice in the orthorhombic phase and of the Cu(2) sublattice in the tetragonal phase, respectively, is monitored via the magnetic splittings at the various Fe sites. Possible assignments of Cu(1) and Cu(2) sites as well as different oxygen configurations around the substituted Fe ions are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02407691
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of chemical substitution on the valence of Eu IN EuNi5 (1986)
    Springer
    Hyperfine interactions 28 (1986), S. 1059-1062 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effects of substituting Eu by other rare-earth elements on the valence of Eu in EuNi5 was studied using the 21.7-keV Mössbauer resonance of151Eu. The experimental results support the view of a dominant influence of the local electronic structure on the valence of Eu as compared to the unit-cell volume.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02061627
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  • 9
    Electronic Resource
    Electronic Resource
    Crystal field interaction at Tm in TmZn2 (1988)
    Springer
    Hyperfine interactions 40 (1988), S. 429-432 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Quadrupole interaction data measured at the C2v Tm site in paramagnetic TmZn2 are analysed in terms of four crystal field parameters using an approach based on the superposition model. The fitted crystal field is demonstrated to predict the anticipated magnetic alignment as well as the sign and asymmetry of the quadrupole interaction in the magnetically ordered state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02049134
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