We report the observation of novel flux motion in single-crystal superconducting Tl2Ca2BaCu2Oχ. Application of a field H≤1 kG following zero-field cooling results in typical logarithmic flux creep, with a peak in δM/δln t near 18 K. Above 50 K, different flux dynamics are observed: an exponential decrease in the diamagnetic moment that gives way near 70 K to the appearance of reverse creep, i.e., increasingly negative magnetization. This latter effect begins after a temperature- and field-dependent wait time. While conventional theory explains inward flux creep, we must invoke flux-line roughening, drive by pinning randomness, to give rise to reverse creep.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering