G. Fuchs

Pinning behavior and magnetic relaxation in melt-processed YBCO doped with Li, Ni and Pd

Abstract Magnetic properties of melt-processed YBCO doped with different content of Li, Ni and Pd impurities are reported. The increase of critical currents of doped materials has been observed in intermediate magnetic fields. The normalized pinning force is scaled into a single curve for all measured isotherms (60–77 K) for the samples with higher impurities level. The analysis of magnetic relaxation measurements at a field of 1 T and in the temperature interval between 10 and 70 K reveals a logarithmic dependence of the effective activation energy vs. current density. The observed time dependence of the magnetization in doped materials can be described in the framework of collective pinning theory.

16 T trapped fields in modified YBaCuO: materials aspects

The maximum field B0 ¼ 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 þ Y200 (þPt) 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. � 2002 Elsevier Science B.V. All rights reserved.

Trapped fields beyond 14 tesla in bulk YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

Bulk YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// 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.

Superconducting permanent magnets and their application in magnetic levitation

Abstract Superconducting permanent magnets form a completely new class of permanent magnets. Of course, they must be cooled to 77 K or below. At very low temperatures (24 K) their magnetization can be a factor of 10 higher than that of the best conventional magnets, providing magnetic forces and energies which are up to two orders of magnitude higher. These new supermagnets became only recently available by the extreme improvement of the quality of melt-textured massive YBa2Cu3Ox samples. Besides having a high magnetization, these superconducting permanent magnets can freeze in any given magnetic field configuration allowing completely new applications like superconducting transport systems or superconducting magnetic bearings.

Anomalous magnetic ordering in PrBa2Cu3O7−y single crystals: evidence for magnetic coupling between the Cu and Pr sublattices

Abstract In Al-free PrBa2Cu3O7−y single crystals the kink in the temperature dependence of magnetic susceptibility χab(T), connected with Pr antiferromagnetic (AFM) ordering, disappears after field cooling (FC) in a field H‖ab-plane. The kink in χc(T) remains unchanged after FC in H‖c-axis. As a possible explanation, freezing of the Cu magnetic moments, lying in the ab-plane, caused by FC in H‖ab, hinders their reorientation and, due to coupling between the Pr and Cu(2) sublattices, ordering of the Pr3+ moments. A field-induced phase transition and a field dependence of the Pr3+ ordering temperature have been found for both H‖c and H‖ab.

Melt-processed YBCO doped with Ca and Cd: comparison of superconducting properties

Abstract We report studies of magnetic properties of bulk melt-processed YBa 2 Cu 3 O 7− δ based material (YBCO), doped with Ca and Cd. The superconducting parameters such as critical temperature, irreversibility field and critical current are found to be strongly dependent both on Ca content and oxygen variation in the (Y,Ca)BCO samples. In contrast, no pronounced change of superconducting properties of Cd doped YBCO has been observed in the wide range of Cd substitution before and after annealing. No scaling of the normalized pinning forces at different temperatures has been found for a Cd content varying between 0.1 and 1 wt.% as well. It is suggested that only a small amount of Cd is incorporated into the YBa 2 Cu 3 O 7− δ phase.

Weak interband coupling in Mg10B2 : A specific-heat analysis

The superconducting state of Mg

High density nanocrystalline MgB/sub 2/ bulk superconductors with improved pinning

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High trapped fields in bulk YBCO encapsulated in steel tubes

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Suppression of superconductivity in RxY1−xNi2B2C compounds by paramagnetic impurities

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