Effect of twin planes in the magnetization hysteresis loops of single crystals

The angular dependence of the critical currents is investigated in a moderately twinned (Formula presented) (NdBCO) single crystal in the temperature range (Formula presented) 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 (Formula presented) The effect of twin planes disappeared at external fields declined more than (Formula presented) from the (Formula presented) axis (twin planes). In this case, the hysteresis loops exhibited a clear fishtail shape. The intermediate peak observed previously in NdBCO single crystal at (Formula presented) is identified with the low-field limit of the twin plane activity.