Attraction and repulsion forces in melt-textured and sintered YBCO-superconductors: a comparative study (original) (raw)
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Journal of Physics: Conference Series, 2008
We have studied experimentally the influence of transverse ac magnetic fields on the levitation force arising between a permanent NdFeB magnet and a bulk melt-textured HTSC YBCO superconducting sample. The axes of superconducting disc and cylindrical magnet were coinciding while the transverse ac magnetic field generated by resistive coil was directed parallel to surface of a disc i.e., perpendicular to the disc axis. We found that application of both impulse and alternative transverse magnetic fields results in suppression of the value of levitation force and its relaxation rate. Namely, the variable magnetic field with amplitude 12 mТ, that approximately in 20 times is less than field of a constant magnet, causes suppression of force more than twice. Monotonous behavior of value of levitation force reduction with the increase in transverse magnetic field amplitude was observed. The possible origin of observed phenomenon is discussed.
Journal of Alloys and Compounds, 2000
We report the isothermal magnetization curves of a YBCO superconducting sample prepared by a flame-quench-melt-growth (FQMG) method. Hysteresis loops have been calculated and analyzed in the framework of a critical state model including the Meissner current. The bulk critical current and Meissner current as a function of applied field were extracted, and the volume fraction of the grains, f , has been g estimated to be 0.64 from a comparison of the theoretical and experimental M-H hysteresis loops. The lower critical field, m H , was 0 c1 found to be 14.4 mT.
Levitation and Suspension Forces Measurement System for High TC Superconductors
MOMENTO
The interaction forces, attraction (suspension) and repulsion (levitation) between a permanent magnet and diferent bulk Yttrium-based superconductors were carried out with an automatic system developed in our group, which is reproducible, reliable and low cost. Two superconducting samples of YBa2Cu3O7-δ (YBCO) prepared by solid-state reaction method (S) and by the melt-textured growth method (MTG) were used. Both samples were characterized by XRD technique and presented the characteristic peaks and intensity relations of the YBCO-123 superconducting phase. Oxygen deficiencies δ > 0,15 and δ < 0,10 for the S and MTG samples respectively, were observed. Both samples displayed diferent hysteresis behavior in the Force (F) vs. Distance (z) measurements when they were field cooled (FC) and zero field cooled (ZFC). This behavior agrees with hysteresis loops observed in magnetization measurements. Both levitation and suspension phenomena were observed in the MTG sample with large hys...
2005
Y0.5 Er 0.5 Ba2 Cu307-8 superconductors with Er2 O3 addition were prepared by partial melting and the effects of excess Er2 03 addition on the magnetic levitation force (MLF) of the partial-melted samples have been investigated. A non-linear relationship was observed between the MLF measured at 77 K and the amount of Er2 O3. It was found that the optimum amount of excess Er2 O3 for enhanced MLF is 10 wt.%. X-ray powder diffraction analysis showed formation of major 123 phase with minor 211 non-superconducting phase for all samples. The results were discussed in detail and the presence of 211 impurities is suggested to act as pinning centers in the 123 samples.
Magnetization and magnetic suspension of YBa2Cu3Ox-AgO ceramic superconductors
Journal of Magnetism and Magnetic Materials, 1989
The magnetic force which accounts for the newly-discovered suspension of a superconductor below a pemmnent magnet is determined by the magnetization of the superconductor and the magnetic-field gradient. Magnetization measurements were carried out on a series of YBa,CusO,-AgO ceramic superconductors, with T, = 93 K. The samples were from the set of samples in which the magnetic-suspension phenomenon was fiit discovered. Magnetization data were taken at 4.2 and 77 K in magnetic fields up to 180 kOe. Hysteresis loops at low fields, up to 1.2 kOe, were also studied at 4.2,77 and 87 to 88 K. The magnetization and hysteresis in most of the samples are among the largest observed to date in ceramic high-T, superconductors. In most of our samples, the remanent moment at 4.2 K is about 80 emu/g, and about 3 emu/g at 77 K. The large magnetization and hysteresis indicate the presence of strong pinning forces. The strong hysteresis at 77 K results in an appreciable positive magnetization, parallel to the field, when the field H is decreased from a finite value (above = 0.5 kOe). This positive magnetization increases with decreasing H. The positive magnetization can be. produced by bringing a permanent magnet close to the superconductor, and then withdrawing it slowly. This leads to an attractive magnetic force between the superconductor and the permanent magnet. Calculations, based on a realistic model, show that at 77 K this magnetic attraction can be sufficiently strong to balance the gravitational force. As a result, the superconductor can be suspended below a permanent magnet. The expected damped oscillatory motion near the suspension point, following the application of a vertical impulse to the superconductor, is discussed. This motion is more complicated than that near the bottom of a conventional potential well. Some remainin g problems associated with the magnetic-suspension phenomenon are outlined.
Field-cooled magnetization of YBa 2Cu 3O 7− δ superconductors
Physica C-superconductivity and Its Applications, 2000
DC susceptibility as a function of temperature was measured in both ®eld-cooled cooling and warming modes in magnetic ®elds in the range of 10 mT 6 l 0 H a 6 7 T on a variety of YBa 2 Cu 3 O 7Àd samples, comprising dierent single crystals, melt-processed bulks and polycrystalline samples, with and without KClO 3 addition. The Meissner curves measured at a ®eld of 1 mT reveal that all the samples are of a single phase. However, with increasing applied ®elds, the superconducting transitions of the single crystals and the melt-processed samples develop kinks, and above 4 T, even a secondary transition can be observed. At low temperatures, the ®eld-cooled moment increases in all samples, except the KClO 3 -doped samples, where a clear decrease is observed. These features are discussed in detail. Further, we discuss the correlation between the kinks in the DC susceptibility and the appearance of the ®shtail shape of magnetization hysteresis loops. Ó
MAGNETIZATION AND HYSTERESIS PROPERTIES OF SUPERCONDUCTING YBa2Cu3O7–x THIN FILMS
High Tc Superconductors, 1989
Magnetic properties of textured superconducting YBa,Cu,O, x thin films prepared by r.f. reactive sputtering are reported. Initial magnetization curves and hysteresis loops have been measured at several temperatures for fields parallel and perpendicular to the film. Hysteresis losses have been studied as a function of maximum applied field. The results are consistent with the Bean model of the critical state and with the H,, values reported for single crystals. 0022.5088/89/$3.50 ((1 Elsevier Sequoia/Printed in The Netherlands
Physica C: Superconductivity, 2003
The forced oscillations of a permanent magnet levitating over a superconducting sample are studied for different magnitudes of the external force. Results are discussed in terms of the one-dimensional model of a forced damped oscillator. It is found that there are two regimes, characterized by sudden and hysteretic changes in the waveform, frequency of resonance, and amplitude of oscillation. These changes are associated with the process of pinning/depinning of the vortex lattice, that produces also two different dependences of the amplitude of oscillation with temperature. On the other hand, it was demonstrated that it is possible to accurately monitor the superconducting transition by measuring the resonance peak changes with temperature.
Science in China Series G, 2004
A novel layer deletion method is used to experimentally investigate the effect of induced shielding current transmission (ISCT) in the longitudinal direction on the levitation force of a single-domain YBa2Cu3OT_• (YBCO) cylindrical superconductor (r215 mm). In the experiment the sample was gradually sliced into two equal sheets, at the middle height along a diameter with 5 mm every step. The experimental results show that the levitation force is closely related with the ISCT in the longitudinal direction. Any layer deletion, even a small piece of layer deletion can reduce the levitation force of the sample. After the whole layer was deleted the levitation force can diminish about 50%. It is also found that the levitation force is directly proportional to the effective factor of surface area, which is equal to the top surface area divided by the total surface area parallel to the top surface of the sample.