Frequency dependence of AC susceptibility in high-temperature superconductors: Flux creep and critical state at grain boundaries
✍ Scribed by K.-H. Müller
- Publisher
- Elsevier Science
- Year
- 1990
- Tongue
- English
- Weight
- 438 KB
- Volume
- 168
- Category
- Article
- ISSN
- 0921-4534
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✦ Synopsis
The loss peak of the AC susceptibility in polycrystalline high-To superconductors shifts slightly to higher temperatures with increasing frequency of the applied AC magnetic field. It is shown that a flux creep term, added to the current density term in the critical state equation, can account for the observed frequency dependence. The magnitude of the peak shift is predicted to increase with decreasing average grain size and decreasing grain boundary junction current density. The model predictions are compared with the experimental data of Nikolo et al. Some of the parameters used in the calculation are determined by fitting data for X' and X" over the full temperature range using a recently developed model for granular superconductors. In addition, the relation between the intergranular pinning potential and the activation energy, which is extracted from log-frequency versus inverse X"-peak temperature data, is clarified.