Magnetic measurements of the upper critical field of YBa 2 Cu 3 O 7 − δ single crystals

摘要: dc magnetization measurements in fields up to 5 T on single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ reveal a well defined onset diamagnetism allowing unique magnetic determination the upper critical field and its anisotropy. The upper-critical-field slopes are -1.9 -10.5 T/K corresponding coherence lengths 16 3 A\r{} for perpendicular parallel CuO planes. At magnetically determined nucleation temperatures no distinct features found resistive transition curves.