Plasticity and memory effects in the vortex solid phase of twinned YBa2Cu3O7 single crystals

We report on marked memory effects in the vortex system of twinned YBa2Cu3O7 single crystals observed in ac susceptibility measurements. We show that the vortex system can be trapped in different metastable states with variable degree of order arising in response to different system histories. The pressure exerted by the oscillating ac field assists the vortex system in ordering, locally reducing the critical current density in the penetrated outer zone of the sample. The robustness of the ordered and disordered states together with the spatial profile of the critical current density lead to the observed memory effects

Thick film YBCO receive coils for very low field MRI

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The synthesis and characterization of (Tl0.6Pb0.2Bi0.2) (Sr1.8Ba0.2)Ca2Cu3O9+x powder and Ag-sheathed tape

We have prepared a single-phase superconducting Tl-1223 powder with Tc above 110 K and used this promising material to produce Ag-sheathed tape. The powder was synthesized by partially substituting Pb and Bi for Tl, and substituting Sr for Ba in a stoichiometry (Tl0.6Pb0.2Bi0.2)(Sr1.8Ba0.2)Ca2Cu3O9+x suggested by Liu et al. The accelerated formation and stabilization of the Tl-1223 phase was observed. The non-agglomerated powder was found to have a homogeneous platelike morphology with average grain size 4.5 μm and maximum grain size 18 μm. The intragrain critical current density was determined to be 6.3*107 A cm-2 at 5 K, 1 T, and 6.5*104 A cm-2 at 77 K, 1 T. Ag-sheathed tapes were fabricated with this powder and magnetic and transport critical current densities of as-rolled tapes and heat-treated tapes were measured. A transport critical current density of 5.6*103 A cm-2 was obtained at 77 K, O T. The relationship between processing conditions, microstructure, and superconducting properties of the tape were also investigate

The critical state in YBa₂Cu₃O_7-x high temperature superconductor

A practical method was devised for measurements of the diamagnetic response of high temperature superconductor specimens. The method is useful for the study of the temperature and field dependencies of the local magnetic induction and its two-dimensional visualisation B(T,Ha,x,y) with a resolution of 0.1 gauss and spatial resolution of 0.1 mm in the plane of the specimen surface. The proposed method facilitates quite simple and quick measurements at liquid nitrogen temperature and in applied Ha magnetic field in excess of 1 T. Cross-shaped miniature Hall probes (HPs) of thin film n-InSb on semi-insulating substrate i-GaAs with a small magnetically sensitive zone of 0.1 × 0.1 mm2 were used as measuring transducers. The high degree of doping of n-InSb layers (n ~ 1018 cm-3) resulted in a sensitivity of 5–7 μV mT-1 (with nominal current up to 10 mA through HPs) and thermosensitivity of less than 0.03% K-1, and made it possible to operate without the need for thermal stabilization of transducers. This method enabled us to study anisotropy of the critical current densities (Jc) of elt-grown YBa2Cu3O7-x pellets. Also, we have been able to determine local cracks and grain connectivity in the YBa2Cu3O7-x pellet samples