P. Verges

Leibniz Institute for Solid State and Materials Research Dresden, Dresden, Saxony, Germany

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Publications (64)77.39 Total impact

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    ABSTRACT: We have proposed to build a 100 T/10 ms, 70 T/100 ms, 60 T/1 s pulsed field user facility with a 50 MJ capacitor bank at the Forschungszentrum Rossendorf near Dresden. This would provide the appealing possibility to have access to Zeeman energies in the energy range of the infrared free-electron-lasers (5 μm to 150 μm; 2 ps; cw; > 10 W) now under construction at the radiation source ELBE (superconducting electron linear accelerator; 40 MeV; 1 mA; 2 ps; cw) in Rossendorf. The work is accompanied by computer simulations of the planned coil systems, of the power supply, and by the development of high-strength conductors aiming at a tensile strength of about 1.5 GPa at σ ≈ σ Cu/2 (microcomposite CuAg alloys and Cu-steel macro compounds). With a view of gaining experience in the construction and operation of pulsed magnets, a pilot pulsed field laboratory was established at the Institute of Solid State and Materials Research Dresden (IFW Dresden). The laboratory includes short pulse magnets with peak field up to 60 T in a 24 mm bore and a rise time of about 10 ms (coil from NHMFL, Tallahassee), and a 40 T long pulse magnet with 24 mm bore and rise time of about 80 ms (coil from METIS, Leuven). The repetition rate of 20 min between pulses is limited by the cooling time of the coils. The coils are energized by a 1 MJ, 10 kV capacitor bank with some special features. With this set-up measurements of magnetization and magnetotransport on 4f-electron systems, for example RECu2, have been out in the temperature range of 1.5 to 300 K and at fields up to 52 T using high precision pick-up coils.
    International Journal of Modern Physics B 01/2012; 16(20n22). · 0.46 Impact Factor
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    ABSTRACT: The trapped field properties of bulk melt-textured YBCO material were investigated at different temperatures. In the temperature range of liquid nitrogen, maximum trapped fields of 1.1 T were found at 77 K by doping of YBCO with small amounts of zinc. The improved pinning of zinc-doped YBa2Cu3O7−x (YBCO) results in a pronounced peak effect in the field dependence of the critical current density. the trapped field at lower temperatures increases due to the increasing critical current density, however, at temperatures around 50 K cracking of the material is observed which is exposed to considerably tensile stresses due to Lorentz forces. Very high trapped fields up to 14.4 T were achieved at 22.5 K for a YBCO disk pair by the addition of silver improving the tensile strength of YBCO and by using a bandage made of a steel tube. The steel tube produces a compressive stress on YBCO after cooling down from 300 K to the measuring temperature, which is due to the higher coeeficient of thermal expansion of steel compared with that of YBCO in the a,b plane. The application of superconducting permanent magnets with trapped fields of 10 T and more in superconducting bearings would allow to obtain very high levitation pressures up to 2500 N/cm2 which is two orders of magnitude higher than the levitation pressure achievable in superconducting bearings with conventional permanent magnets. The most important problem for the application of superconducting permanent magnets is the magnetizing procedure of the YBCO material. Results of magnetizing YBCO disks by using of pulsed magnetic fields will be presented.
    10/2007: pages 685-696;
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    ABSTRACT: This paper will deliver insight into technology and physics of the levitation system for the SupraTrans project, a prototype of a superconducting transportation system. The technology used herein bases on the flux pinning in melt-textured bulk YBa2Cu3O7−X (YBCO) that stabilizes the lateral and the vertical position of the vehicle above the magnetic track. A track made from permanent magnets and soft magnetic steel-yokes acting as flux collectors has been designed and its capability is presented. The concept also includes a fast electromagnetic turnout switch to establish a highly branched transportation network. .
    Journal of Physics Conference Series 01/2006; 43(1).
  • ISMST 8, 8th int. Symposium on magnetic suspension technology, Dresden, DE; 08/2005
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    ABSTRACT: SupraTrans is an innovative transportation concept based on the principle of superconductive magnetic levitation. The aim of the project is to create a fully working prototype, which proves its ability for passenger transport by explicit consideration of the compatibility between systems for propulsion, safety, positioning, power supply, transport logistics and the levitation system itself. The SupraTrans technology uses the flux pinning in high temperature superconductors (HTS) to stabilize the lateral and vertical position of the vehicle on the magnetic track. This self-stabilizing system is the main advantage of the superconductive levitation in comparison to all other levitation systems, which need electronic control and power to keep a constant distance between the train and the track.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
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    ABSTRACT: After the levitation force relaxation was studied for different field-cooling height and working-levitation height, the high-temperature superconductor (HTS) bulk was horizontally moved in the lateral direction above the permanent magnet guideway. Both levitation and guidance force were collected by the measurement system at the same time. It was found that the decay of levitation force is dependent on both the maximum lateral displacement and the movement cycle times, while the guidance force hysteresis curve does not change after the first cycle. This work provided scientific analysis for the HTS maglev system design.
    Applied Physics Letters 05/2005; 86(19):192506-192506-3. · 3.52 Impact Factor
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    ABSTRACT: The magnetoresistance (MR) of cold-pressed powder pellets of the half-metallic ferromagnet CrO2 was measured in wide ranges of temperature T and magnetic fields H up to μ0H=16 T. The MR increases from 2% at 300 K up to 64% at T=1.5 K and no saturation is observed up to 16 T. The low field resistivity depends logarithmically on temperature whereas the high-field MR shows a scaling behavior with H/T. The results favor second-order tunneling (paramagnetic assisted tunneling) at zero bias via localized magnetic moments at or within the barrier between the CrO2 grains as the dominant resistivity mechanism for both the low- and high-field MR, respectively.
    Journal of Magnetism and Magnetic Materials 01/2005; · 2.00 Impact Factor
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    ABSTRACT: Acknowledgments This work was funded by the Sächsische Aufbaubank (SAB) and Sächsisches Staatsministerium für Wirtschaft und Arbeit (SMWA). Acknowledgments also to G. Krabbes for providing bulk YBCO material, to W. Pfeiffer for the link to industrial partners and to T. Riederich for the laboratory and measurement support. Abstract This paper will deliver insight into technology and physics of the levitation system for the SupraTrans project, a prototype of a superconducting transportation system. The technology used herein bases on the flux pinning in melt-textured bulk YBCO that stabilizes the lateral and the vertical position of the vehicle above the magnetic track. A track made from permanent magnets and soft magnetic steel-yokes acting as flux collectors has been designed and its capability is presented. The concept also includes a fast electromagnetic turnout switch to establish a highly branched transportation network.
    01/2004;
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    ABSTRACT: We report on the temperature dependence of the maximum trapped field B o(T) in the high-T c superconductor YBa2Cu3O7–x (YBCO). Trapped fields of bulk melt-textured YBCO samples are limited by their pinning behaviour and mechanical properties. The mechanical properties of bulk YBCO samples were improved by the addition of silver. Furthermore, the YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process. High trapped fields up to 13.3 T were measured at 33 K on the surface of a single YBCO disk containing Ag additions and reinforced with steel tubes. The flux pinning properties of this YBCO disk were improved by neutron irradiation and Zn doping resulting in a significant shift of the trapped field curve B o(T) to higher temperatures. In YBCO mini-magnets, consisting of two YBCO disks, maximum trapped fields up to 16.0 T were achieved at 24 K by a combination of Zn-doping and Ag addition. The improved reinforcement, which was used in this case, was found to withstand the maximum trapped field of 16 T without cracking.
    Journal of Low Temperature Physics 09/2003; 133(1):159-179. · 1.18 Impact Factor
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    ABSTRACT: We report on the temperature dependence of the trapped field in neutron irradiated YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> bulk melt-textured materials. The field trapping capability of these materials at low temperatures is limited by their mechanical properties. We observe that samples without reinforcement usually break during activation at temperatures of around 50 K. Two reinforcement techniques were tested. Resin impregnation is found to be less effective than stainless steel bandaging to compensate for the magnetic stress generated during activation. The resin impregnated samples crack during activation at temperatures of around 45 K. Stainless steel bandaging improves the mechanical properties of the YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> samples and trapped fields of up to 13.3 T were achieved at 33 K.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
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    ABSTRACT: The pinning forces and trapped fields obtained in bulk YBa <sub>2</sub> Cu <sub>3</sub> O <sub>7</sub> (YBCO)-based material doped with Li are compared with results reported for melt-processed samples doped with Zn. The increase of the volume pinning force of Li doped material is twice that of Zn doped YBCO at 77 K. This leads to 20% higher magnetic fields trapped in the Li-doped sample at 77 K. © 2002 American Institute of Physics.
    Applied Physics Letters 01/2003; · 3.52 Impact Factor
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    ABSTRACT: The pinning forces and trapped fields obtained in bulk YBa2Cu3O7 based material doped with Li are compared with results reported for melt-processed samples doped with Zn. The increase of the volume pinning force of Li doped material is twice that of Zn doped YBCO at 77 K. This leads to 20% higher magnetic fields trapped in the Li-doped sample at 77 K. The measurements of the magnetic relaxation at a field of 1 T reveals that the activation energy above 65 K is higher for the Li-doped sample indicating that Li impurities are more effective in increasing the pinning energy.
    Physica C Superconductivity 01/2003; 392:540-544. · 0.72 Impact Factor
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    ABSTRACT: We report on very high trapped fields (13.3 T at 33 K) achieved in bulk YBa2Cu3O7−δ melt-textured monoliths, which were reinforced by steel tubes to compensate the tensile stress generated during activation. The flux pinning properties were improved by neutron irradiation. The resulting increase of the critical current density shifts the maximum attainable trapped fields to higher temperatures (by about 10 K). © 2002 American Institute of Physics.
    Applied Physics Letters 07/2002; 81(5):868-870. · 3.52 Impact Factor
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    ABSTRACT: Trapped fields up to 16 T were achieved at 24 K in superconducting mini-magnets consisting of two bulk YBCO disks. The YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process and to avoid cracking of the material. Additionally, Ag and Zn additions were used for improving the mechanical and the pinning properties of the superconductor, respectively.
    Physica C Superconductivity 01/2002; · 0.72 Impact Factor
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    ABSTRACT: A novel magnetic pair-making interaction between Mn and Ru shows a strong correlation between the magnetic ordering and electronic transport, which was well exemplified in the investigation of bulk polycrystalline samples of La0.7Pb0.3Mn1⊟xRuxO3 and La0.6Pb0.4Mn1⊟xRuxO3, where 0.0 ≤ x ≤ 0.4. The metal-insulator transition (Tρ) complementing the Curie temperature (Tc) was observed up to 30% of Ru in La0.7Pb0.3Mn1⊟xRuxO3, and extended up to 40% of Ru in La0.6Pb0.4Mn1⊟xRuxO3, showing a unique double-exchange ferromagnetic exchange interaction between Mn and Ru ions. An upturn in resistance due to charge carrier localization at low temperatures (T<0.5 Tc) for more than 20% Ru doping was due to a dominant hole carrier density contribution rather than to grain boundary effects as inferred from the scanning electron microscopy and energy dispersive x-ray studies of the samples sintered at 1200 and 1400 °C. The charge localization effect of the eg electrons was removed by tuning the hole carrier density as demonstrated in the La0.6Pb0.4Mn1⊟xRuxO3 samples. Long range correlations between magnetism and transport in this series was attributed to the presence of mixed valence Ru(IV/V) and Mn(III)/(IV) pair, which shows a unique double exchange mediated interaction.
    Journal of Materials Research - J MATER RES. 01/2002; 17(12):3090-3097.
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    ABSTRACT: The maximum field B0=16 T was trapped at 24 K in the gap of a mini-magnet made of two cylindrical samples. B0 on top of a single cylinder was 12.5 T at 20 K and 9 T at 40 K. The YBa2Cu3O7 based bulk material was prepared by the modified melt crystallization process from Y123+Y200 (+Pt) precursor with 12 wt.% Ag forming silver precipitates in the as grown materials. A bandage of stainless steel compensated the tensile stress during magnetization. The unfavorable influence of admixed Ag on the critical current density jc was compensated by doping with Zn ions.
    Physica C Superconductivity 01/2002; · 0.72 Impact Factor
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    ABSTRACT: Improved trapped fields are reported for bulk melt-textured YBa <sub> 2 </sub> Cu <sub> 3 </sub> O <sub>7-δ</sub> (YBCO) material in the temperature range between 20 and 50 K. Trapped fields up to 12.2 T were obtained at 22 K on the surface of single YBCO disks (with Ag and Zn additions). In YBCO minimagnets, maximum trapped fields of 16 T (at 24 K) and of 11,2 T (at 47 K) were achieved using ( Zn+Ag ) and Zn additions, respectively. In all cases, the YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process and to avoid cracking. We observed cracking not only during the magnetizing process, but also as a consequence of flux jumps due to thermomagnetic instabilities in the temperature range betweeen 20 and 30 K. © 2001 American Institute of Physics.
    Applied Physics Letters 12/2001; · 3.52 Impact Factor
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    ABSTRACT: Bulk YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> material with single-domain grains up to 35 mm in diameter was prepared by a modified melt-texturing process. The pinning properties were improved by chemical doping of Zn on Cu plane sites resulting in a well pronounced peak effect in the field dependence of the critical current density. Trapped fields of more than 1.1 T at 77 K have been obtained in a zinc-doped YBCO disk of only 27 mm in diameter. Higher trapped fields are observed at lower temperatures due to the increasing critical current density, however, at temperatures between 50 and 20 K, the trapped field is limited by the mechanical properties. Using a bandage made of steel, very high trapped fields were achieved in the 1 mm gap between two YBCO disks. Trapped fields up to 14.4 T were found at 22.5 K in such minimagnets containing silver precipitates, whereas the trapped fields of zinc-doped minimagnets reached values of 11.2 T at 47 K
    IEEE Transactions on Applied Superconductivity 04/2001; · 1.20 Impact Factor
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    ABSTRACT: Bulk YBa2Cu3O7−x (YBCO) material with single-domain grains up to 35mm in diameter was prepared by a modified melt-texturing process. A maximum trapped field, B0, up to 1.1T at 77K was obtained on the top of a single YBCO disk 25mm in diameter by chemical doping of Zn on Cu plane sites increasing up to 9T at 43K due to the increasing critical current density at lower temperatures. At temperatures around 50K, the trapped field is limited by the mechanical properties and cracking of the material which is exposed to considerable tensile stresses due to Lorentz forces acting during the magnetization procedure on the superconductor. Very high trapped fields up to 14.4T were achieved at 22K in the gap betweeen two YBCO disks by the addition of silver improving the fracture toughness of the material and by using a bandage made of steel. This is the highest trapped field achieved so far in a bulk superconductor. On the top of a single YBCO disk, a maximum trapped field of 11.5T was obtained at 17K. In order to use superconducting YBCO permanent magnets in superconducting magnetic bearings, an effective method for magnetizing the superconductor is required. Results of magnetizing YBCO samples by applying pulsed magnetic fields will be presented.
    Physica B Condensed Matter 01/2001; 294(4):398-401. · 1.28 Impact Factor
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    ABSTRACT: Large grain bulk superconductors with various compositions: SmBa2Cu3O7−δ, (Sm0.5Eu0.5)Ba2Cu3O7−δ, and EuBa2Cu3O7−δ have been successfully fabricated in air. The scaling studies of the volume pinning force evidenced two competitive pinning contributions at low and high fields for all compositions. The analyses of the scaling curves showed that the low field pinning kept identical for three compositions, while in high fields, the dominant pinning for Sm123 and Eu123 was the small-sized normal core pinning and the δTc pinning in SE123.
    Developmental Brain Research - DEVELOP BRAIN RES. 01/2001; 357:461-465.