Showing papers by "G. Krabbes published in 2000"
TL;DR: In this article, high trapped fields were found in zinc-doped, bulk melt-textured YBa2Cu3O7−x (YBCO) material showing a pronounced peak effect in the field dependence of the critical current density.
Abstract: High trapped fields were found in zinc-doped, bulk melt-textured YBa2Cu3O7−x (YBCO) material showing a pronounced peak effect in the field dependence of the critical current density Trapped fields up to 11 T were found at 77 K at the surface of a YBCO disk (diameter 26 mm, height 12 mm) Very high trapped fields up to 1435 T were achieved at 225 K for a YBCO disk pair (diameter 26 mm, height 24 mm) by the addition of silver and using a bandage made of stainless steel The pinning forces and trapped fields obtained in bulk YBCO material are compared with results reported for melt-processed NdBa2Cu3O7−x and SmBa2Cu3O7−x
143 citations
TL;DR: In this article, a modified melt crystallization process (MMCP) was applied to prepare single grain YBCO bulk material with Zn partially substituting for Cu. Hole doping was controlled by an appropriate oxidizing treatment of the as-grown bulk.
Abstract: The previously introduced modified melt crystallization process (MMCP) has been applied to prepare single grain YBCO bulk material with Zn partially substituting for Cu. Hole doping was controlled by an appropriate oxidizing treatment of the as-grown bulk. A field induced pinning was indicated by a well pronounced peak of the critical current density jc in the jc vs. H relationship for the maximal oxidized (overdoped) material containing Zn, whereas pure overdoped YBCO shows no peak effect. The peak effect for Zn-doped YBCO appearing for T=77 K at a relatively high field of about 3 T can be attributed to pair breaking by locally induced magnetic moments due to in plane Zn for Cu substitution. Besides high quality of the bulk YBCO, the peak effect is the reason for the trapped field as large as 1.12 T at 77 K in the cylinder of only 25 mm in diameter.
130 citations
TL;DR: In this paper, the chemical and physical conditions under which U/n processing is successful are considered, including spacing, S, and size of deposits of U compounds, and neutron absorption by the HTS.
Abstract: Insertion of uranium into HTS precursor powders prior to texturing, and irradiation with thermal neutrons after texturing is called U/n processing. Damage caused by uranium fission fragments has been extensively studied for pinning center behavior in Y123, and Ag-BiSCCO tape. In both HTS systems results for J c , anisotropy, etc. are excellent. We consider the chemical and physical conditions under which U/n processing is successful, including spacing, S, and size of deposits of U compounds, and neutron absorption by the HTS. If δ=length of the quasi-columnar fission fragment defects, we find S
18 citations
TL;DR: In this article, superconductors were melt-processed in air atmosphere starting from an initial precursor consisting of Nd2O3, BaCuO2 and CuO, or Nd-123 and BaCoO2, respectively, to stabilise the process to proceed in equilibrium with compositions along the tie line Nd123-Nd-422, both with its stoichiometric compositions.
Abstract: Nd1+xBa2−xCu3O7−δ (Nd-123) superconductors were melt-processed in air atmosphere starting from an initial precursor consisting of Nd2O3, BaCuO2 and CuO, or Nd-123 and BaCuO2, respectively, to stabilise the process to proceed in equilibrium with compositions along the tie line Nd-123–Nd-422, both with its stoichiometric compositions. The Nd:Ba ratio was stabilised close to 1:2 and high Tc values up to 96 K were achieved. As a result, Jc values of 30 kA/cm2 (0 T) and an expressed peak effect of 10 kA/cm2 arises at an applied external magnetic field of 2 T at 77 K.
11 citations
TL;DR: In this paper, the authors presented results on magnetizing the YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) samples by applying pulsed magnetic fields.
Abstract: Bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) material with single-domain grains up to 35 mm in diameter was prepared by a modified melt-texture process. Trapped fields of 1.1 T at 77 K and of 9 T at 43 K were obtained In zinc-doped YBCO material showing a pronounced peak effect in the field dependence of the critical current density. Very high trapped fields up to 11.4 T have been achieved at 17 K in YBCO material with improved mechanical properties. The tensile strength of this material was enhanced by the addition of silver. Additionally, a stainless steel tube was used in order to strengthen the sample against the magnetic tensile stresses. For application of YBCO samples in superconducting magnetic bearings, it is difficult to magnetize the superconductor to the maximum storable field. The authors present results on magnetizing the YBCO samples by applying pulsed magnetic fields.
9 citations
TL;DR: In this paper, the lower substitution limit was determined to be x≈0.25 and the formation temperature of the members of this solid solution was found to increase from 1350°C to 1500°C with decreasing Sr content.
5 citations
TL;DR: In this paper, the authors investigated the magnetoresistance of polycrystalline samples of the bilayer Ruddlesden-Popper compound La1.2Nd0.6Mn2O7 and showed that at T2=38 K the compound reveals a transition from the ferromagnetic to an antiferromagnetic spin arrangement of alternating bilayers, which undergoes a first order metamagnetic transition towards ferromagnetism in a magnetic field of ∼3.5 kOe at 20 K.
Abstract: Magnetization and magnetotransport have been investigated for polycrystalline samples of the bilayer Ruddlesden–Popper compound La1.2Nd0.2Sr1.6Mn2O7 that shows the colossal magnetoresistance effect connected with ferromagnetic ordering at TC=74 K. At T2=38 K the compound reveals a transition from the ferromagnetic to an antiferromagnetic spin arrangement of alternating ferromagnetic bilayers, which undergoes a first order metamagnetic transition towards ferromagnetism in a magnetic field of ∼3.5 kOe at 20 K. In measurements of resistance vs magnetic field, this transition is accompanied by a large resistance drop of [R(5 kOe)−R(0)]/R(0)=−60% at 5 K. The tunneling-like magnetoresistance (MR) known for current transport perpendicular to the layers in (La, Nd)1.4Sr1.6Mn2O7 single crystals contributes to this large MR observed in a polycrystalline sample. While current is expected to mainly follow the bilayers within the grains due to the anisotropy of conductivity, the high value of resistivity of our sample...
3 citations