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The complex ac susceptibility χ=χ′-jχ″ of a melt-textured YBa2Cu3Ox ring closed by a strong-coupling contact is measured after zero-field cooling to 77 K as a function of the ac field amplitude Hm and frequency f. The resulting χ(Hm,f) is similar to that derived from a power-law relation between the local current density and electric field but with maximum χ″(Hm) increasing steadily with increasing f, which is explained by the creep of Abrikosov-Josephson vortices along the contact driven by the London force of supercurrents and the Lorentz force of the induced normal currents. [ABSTRACT FROM AUTHOR]

The dc and ac magnetic properties of a melt-textured YBa2Cu3Ox ring with a perpendicular crack is studied. It is found that the crack behaves as a resistively shunted very long Josephson junction. However, besides the expected edge currents, certain inner currents have to occur in the junction. This anomaly may be a general feature of a very long junction with similar values of Josephson and London penetration depths, which is a case not yet studied theoretically. [ABSTRACT FROM AUTHOR]

The field-amplitude and frequency dependent complex ac susceptibility of a well sintered YBa2Cu3O7-δ disk has been measured at 77 K, which shows that its intra- and intergranular critical-current densities are determined by the collective flux creep inside the grains and the maximum Josephson currents across the grain boundaries, respectively. While the former is widely recognized, the latter contrasts to a popular belief of a mechanism of Josephson-vortex pinning and creep. [ABSTRACT FROM AUTHOR]

The power-law E(J) characteristic of a superconductor may be determined by ac susceptibility (χ=χ′-jχ″) measurements from the field amplitude at which χ″ takes maximum, Hm(χm″), and frequency f. The relation between E vs J and Hm(χm″) vs f obtained from direct calculations of χ for a long cylinder and a thin disk with a power-law E(J) provides a firm base for the ac susceptibility technique of Jc determination of advanced high-temperature superconductors. [ABSTRACT FROM AUTHOR]

The complex ac susceptibility of YBa2Cu3O7 (YBCO) coated conductor and YBCO single crystal has been measured at 77 K as a function of field amplitude and frequency, from which the E(J) characteristic is deduced. It is shown that the E(J) in the single crystal obeys a power law in a large range above Ec=1 μV/cm, indicating a flux creep mechanism, whereas for the coated conductor there appears a transition from flux creep to flux flow at E∼10Ec. The reported contactless technique may be conveniently used for the research and development of coated conductors. [ABSTRACT FROM AUTHOR]

An inductive methodology simultaneously enabling the determination of grain- and intergrain critical current densities of YBa[sub 2]Cu[sub 3]O[sub 7-x] coated conductors is developed. This noninvasive method is based on the identification of a clear peak in the reverse branch of the magnetization loop at a positive magnetic field, as a signature of the electromagnetic granularity inherent to these materials. A quantitative evaluation of the return magnetic field at the grain boundaries allows us to understand the existence of this magnetization peak and quantify the grain critical current density. This methodology is envisaged to sort out granularity effects from vortex pinning effects on coated conductors. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]