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  • Articles: DFG German National Licenses  (72)
  • 1
    Electronic Resource
    Electronic Resource
    Neutron inelastic scattering studies of UF4 and NpF4 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9338-9343 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Neutron inelastic scattering experiments have been performed on UF4 and NpF4. We had anticipated observing a number of sharp magnetic transitions in these experiments because the tetravalent metal ions are expected to have localized f states. However, very few transitions were observed, three and two in UF4 and NpF4, respectively. Except for the lowest-lying level (at 1.5 meV) in UF4 the transitions are wider than the instrumental resolution, suggesting a strong interaction between the electronic states and lattice vibrations. The levels observed do not correspond to those predicted by a crystal-field scheme recently proposed from optical spectroscopy. However, the paucity of observed levels in our experiments excludes us proposing an alternative scheme. The 1.5 meV energy level in UF4 is in good agreement with that deduced from specific heat and magnetic susceptibility data. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467964
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  • 2
    Electronic Resource
    Electronic Resource
    Magneto-optical imaging of the first order spin-flop transition in the layered manganite La1.4Sr1.6Mn2O7 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5043-5045 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spin-flop transition in the antiferromagnetic layered manganite La1.4Sr1.6Mn2O7 was studied using magnetization measurements and a high-resolution magneto-optical imaging technique. We report the direct observation of the formation of ferromagnetic domains appearing at the first order spin-flop transition. The magnetization process proceeds through nucleation of polarized domains at crystal defect sites and not through the expansion of polarized domains due to domain wall motion. A small magnetic hysteresis is caused by the difference between the mechanisms of nucleation and annihilation of domains in the mixed state. These results establish a direct link between the magnetic structure on the atomic scale as seen in neutron scattering and the macroscopic properties of the sample as seen in magnetization and conductivity measurements. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373242
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of layering and doping on the magnetic anisotropy of the layered manganites La2−2xSr1+2xMn2O7 (x=0.3–0.4) (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6621-6623 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization experiments were performed on a series of single crystals of the bilayer manganites La2−2xSr1+2xMn2O7. The magnetic anisotropy constants were determined by fitting expressions based on the tetragonal anisotropy energy to the magnetization curves. It is shown that there is a significant dipolar contribution to the first order anisotropy constant arising from the layered crystal structure. This contribution determines the magnetization direction in the doping range x=0.32–0.33 where the anisotropy due to the electronic structure is small. With increasing doping the magnetic anisotropy changes from strong uniaxial anong the c axis (K(approximate)2.5×106 erg/cm3) at x=0.3 to strong easy plane (K(approximate)−3.7×106 erg/cm3) at x=0.4 in an almost linear fashion. This evolution is explained through the change of the orbital nature of the eg electrons from predominantly d3z2−r2 to predominantly dx2−y2. On the samples displaying easy-plane anisotropy a small anisotropy in the basal plane of about −7×104 erg/cm3 was determined with (110) being the easy axis. An estimate of the spin-wave gap based on these results is in reasonable agreement with experimental determinations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357136
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  • 4
    Electronic Resource
    Electronic Resource
    Grain boundary structures in La2/3Ca1/3MnO3 thin films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6758-6760 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As with many other oxide-based compounds that exhibit electronic behavior, structural defects have a strong influence on the electronic properties of the CMR manganites. In this work, we have studied the effect of grain boundaries on the transport properties and on the local orientation of magnetization. Thin films of the perovskite-related La2/3Ca1/3MnO3 compound were deposited onto bicrystal substrates using pulsed laser deposition. Transport measurements showed an enhancement of magnetoresistance across the grain boundary. The structure of the boundary was evaluated by electron microscopy. In contrast with the highly meandering boundaries typically observed in bicrystals of high-temperature superconductors, the boundaries in these films are relatively straight and well defined. However, magneto-optical imaging showed that the local magnetization was oriented out of the plane at the grain boundary while it was oriented within the plane in the grains on either side. This coordinated reorientation of local magnetization near the grain boundary leads to enhanced magnetoresistance across the boundary in low fields. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372832
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of the structural phase transition in manganite films by magneto-optical imaging (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5828-5830 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A high-resolution magneto-optical imaging technique is used to reveal the formation of twins occurring during a martensitic phase transition at ∼105 K in La2/3Ca1/3MnO3 (LCMO) films grown on SrTiO3 (STO) substrates. The magnetic contrast arises due to the magneto-elastic tilts of the Mn- magnetic moments in the twins. Different magnetic structures are found in LCMO films grown on MgO, NGO, and LAO substrates showing the importance of the substrate material for the manganite film properties. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372536
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Transport critical current density and microstructure in extruded YBa2Cu3O7−x wires processed by zone melting (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 228-232 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: YBa2Cu3O7−x compounds were extruded into long wires with the diameter of 1 mm after sintering. The sintered wires were subsequently zone melted to develop a highly textured microstructure. Magnetization experiments at 77 K indicated a Jc value of 1×105 A/cm2 at 1 T. Transport measurements at 77 K showed a greatly enhanced field dependence of the critical current density. Transmission electron microscopy revealed an important grain-boundary feature which eliminated the weak-link behavior. Large amounts of dislocations have also been found in the zone-melted sample which may contribute to flux pinning in the system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347122
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  • 7
    Electronic Resource
    Electronic Resource
    Resistive dissipation in imperfect crystals of YBa2Cu3O7−δ (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1268-1271 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured ac magnetoresistance in fields up to 8 T in a variety of YBa2Cu3O7−δ single crystals containing (a) twin boundaries only in one direction, (b) multi-twin domain structure, and (c) growth steps. We find two components of the resistance: an angular dependent Lorentz force induced "excess resistivity'' superimposed on an angular independent resistivity. The temperature and magnetic field dependence of the angular-dependent resistivity exhibit a strong correlation with crystal defects, whereas the angular-independent resistivity remains virtually unchanged. In addition, we find crystals exhibiting both ohmic and non-ohmic behavior in their I-V characteristics depending on crystal imperfections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103458
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetization hysteresis and flux pinning in twinned and untwinned YBa2Cu3O7−δ single crystals (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 84-86 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of the magnetization hysteresis of the same crystal in the twinned and untwinned state reveal that pinning due to twinning planes may contribute a substantial, anisotropic fraction of the observed critical currents. A linear scaling between magnetization hysteresis and sample dimension shows that the twinned and untwinned crystal does not exhibit any subgranular effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104237
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  • 9
    Electronic Resource
    Electronic Resource
    Lattice defects and flux pinning in crystallized metal-oxide glasses in the Bi-Sr-Ca-Cu-O system (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1354-1356 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Large amounts of lattice defects have been observed in the crystallized metal-oxide glasses in the Bi-Sr-Ca-Cu-O system prepared by the rapid solidification method. The density of such defects has been found to greatly increase as the calcium and copper content of the starting material increases. These lattice defects are formed as a result of supersaturation of calcium and copper in the sample matrix. The intragrain critical current density has been found to increase 30 times in magnitude as the density of the lattice defects is increased in the sample matrix. The corresponding flux pinning mechanisms are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101896
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  • 10
    Electronic Resource
    Electronic Resource
    Direct imaging of current sharing in (BiPb)2Sr2Ca2Cu3Ox composite conductors (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 134-136 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a high-resolution magneto-optical imaging technique, we study the flow of transport currents around cracks in monofilament (BiPb)2Sr2Ca2Cu2Ox composite conductors. Shunting through the Ag clad is directly observed. The current in the silver decays exponentially with distance from the crack as expected in a one dimensional distributed resistance model. At 77 K, the transfer length, λ, is approximately 0.56 mm, implying an interface resistivity of 7.5×10−8 Ω cm2. This transfer length is found to increase slightly with increasing temperature. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119451
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