Detailed magnetization study of superconducting properties of YBa₂Cu₃O_7−xceramic spheres

Abstract

We present a magnetization study of low density YBa2Cu3O7−x ceramics carried out in magnetic fields 0.5 Oe < H < 50 kOe. It was demonstrated that superconducting links between grains may be completely suppressed either by a magnetic field H ∼ 100 Oe (at low temperatures) or by an increase of temperature above 70 K. This property of present samples allowed to evaluate the ratio between an average grain size and the magnetic field penetration depth λ. Furthermore, at temperatures T > 85 K, using low-field magnetization measurements, we could evaluate the temperature dependence of λ, which turned out to be very close to predictions of the conventional Ginzburg-Landau theory. Although present samples consisted of randomly oriented grains, specifics of magnetization measurements allowed for evaluation of λ ab (T ). Good agreement between our estimation of the grain size with the real sample structure provides evidence for the validity of this analysis of magnetization data. Measurements of equilibrium magnetization in high magnetic fields were used for evaluation of Hc2(T ). At temperatures close to Tc, the Hc2(T ) dependence turned out to be linear in agreement with the Ginzburg-Landau theory. The value of temperature, at which Hc2 vanishes, coincides with the superconducting critical temperature evaluated from lowfield measurements.

Magnetic Properties and Critical Current of Superconducting Nanocomposites (1 −x)YBa2Cu3O7−δ + xCuO

“…The value of H is approximately equal to value of the field of complete penetration of the magnetic flux into the granules at the given temperature. For H < H p , the expression of the critical state model for J c determination gives underestimated values [14,15]. The estimation of the circulation radii shows that the average size of the granules increases from R = 1.9 μm in the sample with x = 0 to R = 2.…”

“…The value of R depends on the magnetic field. In small fields (less than 100 Oe), R is equal to the radius of the sample [15]. In high fields, the superconductivity of the intergranular boundaries is completely suppressed by the magnetic field, and the magnetic properties of the polycrystalline sample can be determined only by the magnetization of the granules.…”

Superconductivity on Interfaces of Nonsuperconducting Granules La2CuO4 and La1.56Sr0.44CuO4

“…The second is а network of weak links formed inside and between the superconducting areas. These subsystems demonstrate different behavior in magnetic fields and temperatures as well as for polycrystalline superconductors [6,14]. At a low magnetic field (smaller than ~100 Oe), the critical current of the samples is defined by the weak links network.…”

The Effect of the Pressure for the Formation of YBa2Cu3O7–d Bulk Ceramics with Domestic Microwave Oven

“…Technical developments of this kind of superconductors are so attractive to be applied to practical use. Among various materials, YBa 2 Cu 3 O 7-d (YBCO) has been significantly well studied in the wide range of the field on superconducting in a bulk [1] or porous [2] ceramics as well as in a thin-film form. This material is surely supposed to be the most reliable high Tc superconductor.…”