Pinning Force and Time-Dependent Response in a Grain-Oriented Yttrium 1:2:3 Superconductor

Abstract

ABSTRACTX-ray diffraction shows a preferred orientation of the 1:2:3 crystallites with the (ab) planes parallel to the longitudinal axis of the bar-shaped specimen, and a random orientation of the c axes. The dc magnetic hysteresis and time-dependent response were measured parallel to the (ab) planes or parallel to the random axis. The orientation dependence of the shape of the dc magnetic hysteresis proved the anisotropie nature of the flux-line structure and flux pinning. The experimental points were fitted to theoretical equations, allowing quantitative characterization of the orientation and temperature-dependent pinning. Time-dependent response was found to be logarithmic below a critical temperature in the range of 0.5 Tc. Activation energies determined in this region by assuming thermally assisted flux flow were found to be significantly higher than those in polycrystalline YBCO. Several activation processes or steps could be clearly distinguished. The field-cooled and zero-field-cooled specimens did not show significant differences, neither did the transport and magnetic critical current. This proves the presence of clean grain boundaries in this investigated high-quality sample.