Effect of twin planes in the magnetization hysteresis loops ofNdBa2Cu3O7single crystals

Abstract

The angular dependence of the critical currents is investigated in a moderately twinned ${\mathrm{NdBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (NdBCO) single crystal in the temperature range $30<~T<~90\mathrm{K}.$ In intermediate fields around the fishtail peak a reduction of critical current density due to twin structure is observed up to 90 K. This effect implies that vortices retain their three-dimensional character practically up to ${T}_{c}.$ The effect of twin planes disappeared at external fields declined more than $\ensuremath{\theta}\ensuremath{\approx}15\ifmmode^\circ\else\textdegree\fi{}$ from the $c$ axis (twin planes). In this case, the hysteresis loops exhibited a clear fishtail shape. The intermediate peak observed previously in NdBCO single crystal at $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$ is identified with the low-field limit of the twin plane activity.