Detailed magnetization study of superconducting properties of YBCO ceramic spheres

TL;DR

This study investigates the superconducting properties of YBCO ceramic spheres through magnetization measurements, revealing insights into grain coupling, magnetic penetration depth, and critical fields consistent with Ginzburg-Landau theory.

Contribution

It provides a detailed analysis of magnetization data to evaluate the magnetic penetration depth and critical fields in YBCO ceramics, confirming theoretical predictions.

Findings

Superconducting links are suppressed above 100 Oe or 70 K.

The temperature dependence of lambda matches Ginzburg-Landau theory.

Hc2(T) is linear near Tc, aligning with theoretical models.

Abstract

We present a magnetization study of low density YBCO 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 of the order of 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 lambda. Furthermore, at temperatures T > 85 K, using low-field magnetization measurements, we could evaluate the temperature dependence of lambda, 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 lambda_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 T_c, 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 low-field measurements.