Paramagnetic effect at low and high magnetic fields in melt-texturedYBa2Cu3O7−δ (original) (raw)
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Anisotropic magnetization and weak links in melt textured YBa2Cu3O7
Cryogenics, 1993
Textured YBa2Cu307 superconducting samples have been prepared by melt texturing growth (MTG) under variable conditions. We have investigated low field magnetic susceptibility (d.c. and a.c.), high field hysteresis loops and magnetic irreversibility through ZFC-FC temperature scans. We show that low field flux penetration effects, measured by screening capability and dissipative behaviour, may be convenient to detect residual weak links and to characterize the degree of texturation when their anisotropic behaviour is analysed. Critical currents up to 2 x 105 A cm-2 at 1 T and 25 K and for H II c have been obtained and their temperature and field dependence determined. We find that enhanced critical currents in the H II c configuration also lead to an increase in the magnetic anisotropy, which probably reflects reduced misorientation of the crystallites within a domain.
Paramagnetic Meissner effect at high fields in YCaBaCuO single crystal and melt-textured YBaCuO
Physica C-superconductivity and Its Applications, 2010
We report on systematic field-cooled magnetization experiments in an Y0.98Ca0.02Ba2Cu3O7-δ single crystal and melt-textured YBa2Cu3O7-δ samples. Magnetic fields up to 50 kOe were applied and a paramagnetic response related to the superconducting state was observed. We discuss our results in terms of the flux compression scenario into the sample.
Journal of the Korean Physical Society, 2013
In this work we report on systematic field-cooled magnetization experiments in melt-textured YBa2Cu3O 7−δ samples containing Y211 precipitates. Magnetic fields up to 14 T were applied either parallel or perpendicular to the ab planes and a strong paramagnetic response related to the superconducting state was observed. This effect is known as paramagnetic Meissner effect (PME). The magnitude of the PME increases when the field is augmented. This effect shows a strong paramagnetic relaxation, such that the paramagnetic moment increases as a function of the time. The pinning by the Y211 particles plays a crucial role in the explanation of this effect and our results suggest that the pinning capacity can produce a strong flux compression into the sample, originating the PME and the strong time dependence.
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
Paramagnetic moments in YBa2Cu3O7−δ nanocomposite films
Physica C: Superconductivity, 2014
We report on magnetization studies in YBa 2 Cu 3 O 7Àd thin films with dispersed Ba 2 YTaO 6 nanoparticles. The magnetization measurements were made using a superconducting quantum interference device (SQUID) and a vibrating sample magnetometer (VSM). Magnetic moments were measured as functions temperature using zero-field cooling (ZFC) and field-cooled (FC) prescriptions for magnetic fields up to 10 T applied parallel and perpendicular to the ab planes. A paramagnetic response related to the superconducting state was observed during the FC experiments. This effect, known as paramagnetic Meissner effect (PME), apparently increases when the magnetic field is increased. We discuss our PME results in terms of the strong pinning scenario modulated by Ba 2 YTaO 6 nanoparticles dispersed into the superconducting matrix.
Acta Physica Polonica A
The microstructure and magnetic properties of the melt textured YBa2Cu3O7_δ samples prepared by the powder melting process, in which Y2Cu2O5 and BaCuO2 were used as precursors, and those prepared by the quench aud melt growth method are described and compared. The lattice parameters and Tc values for the samples prepared by the both techniques were similar. The penetration and the spatial distribution of the magnetic flux in the superconducting samples was imaged by means of a field-mapping device using a Hall probe. In the range of low magnetic fields up to 820 A m-1 no significant differences in penetration of magnetic flux between the samples prepared by the powder melting process and the quench and melt growth were observed. The mapping could not resolve any grain boundaries, single grains and structural defects. By the ac and virgin volume magnetisation characteristics, which were measured in the zero-field cooled condition by a 2nd order SQUID gradiometer, no weak links were identified. Better magnetic properties of the quench and melt growth samples in high magnetic fields can be explained by the differences in microstructure and/or by the risen content of the finely dispersed 211 and Pt containing phases. The increase factor in magnetisation is about 2.5. Some aspects of the Bean model for textured YBa2Cu3O7-δ samples are discussed.
Magneto-optical studies of magnetization of melt-processed YBa 2 Cu 3 O 7 − δ
Physical Review B, 1997
Magnetization patterns on different faces of long bars cut from melt-processed YBa 2 Cu 3 O 7Ϫ␦ ͑YBCO͒ samples were studied using advanced magneto-optical techniques. It is shown that with an external magnetic field perpendicular to the long side of the bar the magnetization front is described by a cylindrical surface having a cross section shaped as a higher-order ellipse, i.e., the front has a sharper bending near the sample edges than a second-order ellipse. Similar to bicrystal boundaries, the boundaries of structure domains consisting of c axis-aligned crystalline plates are revealed to be weak links in a wide temperature range for misorientation angles between domains exceeding 10°. The temperature dependence of the critical currents inside the domains are determined by fitting induction profiles measured across the bars. From direct flux pattern observations and measurements of the anisotropy for currents flowing along and across the crystalline plates, it follows that the crystallite boundaries also become effective weak links at higher temperatures and fields. Possible reasons for why the observed anisotropy is much less than that for c axis and ab plane currents in YBCO single crystals are discussed. ͓S0163-1829͑97͒00938-7͔
Combined paramagnetic and diamagnetic response ofYBa2Cu3O7
Physical Review B, 2000
It has been predicted that the zero frequency density of states of YBCO in the superconducting phase can display interesting anisotropy effects when a magnetic field is applied parallel to the copper-oxide planes, due to the diamagnetic response of the quasi-particles. In this paper we incorporate paramagnetism into the theory and show that it lessens the anisotropy and can even eliminate it altogether. At the same time paramagnetism also changes the scaling with the square root of the magnetic field first deduced by Volovik leading to an experimentally testable prediction. We also map out the analytic structure of the zero frequency density of states as a function of the diamagnetic and paramagnetic energies. At certain critical magnetic field values we predict kinks as we vary the magnetic field. However these probably lie beyond currently accessible field strengths.
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.
Revista Facultad de Ingeniería, Universidad de Antioquia, 2019
In this paper, we measure the attraction (suspension) and repulsion (levitation) forces produced by the interaction between a permanent magnet and different bulk superconductors. The measurements of the interaction force HTS-PM were carried out with a relatively simple technique developed by us, which is reproducible, reliable and low cost. The obtained results were analyzed with the Bean’s critical-state model assuming a uniform magnetic field applied to the superconductor. Two superconducting samples of YBa2Cu3O7-δ (YBCO) prepared by solid-state reaction method and by the melt-textured growth method (MTG) were used. Both samples presented a different hysteresis behaviour in the field cooling (FC) and zero field cooling (ZFC) regimes. Levitation and suspension phenomena were observed in the MTG sample; however, the sintered sample (S) with Oxygen deficiencies (δ > 0.15) displayed a slight levitation force but did not show a suspension force, the latter one attributed to a more efficient magnetic flux pinning. Additionally, the critical current density of both samples was determined from the maximum gap of the force (ΔF) in the FC regime. The obtained values were between 43.00 A/cm2 and 2,758 A/cm2 for the sintered and MTG samples, respectively. These values show a remarkable difference between sintered and MTG samples like that observed from magnetization measurements, which indicate that attraction and repulsion force measurements could provide a rapid and reliable characterization method of polycrystalline superconducting samples.