The angular dependence of the critical current was investigated in a moderately twinned single crystal at temperatures ranging from 30 to 90K. In intermediate fields around the fishtail peak, a reduction in critical current density due to the twin structure was observed at up to 90K. This effect implied that vortices retained their 3-dimensional character almost up to the critical temperature. The effect of twin planes disappeared in external fields which declined by more than 15º from the c-axis (twin planes). In this case, the hysteresis loops exhibited a clear fishtail shape. An intermediate peak which was observed previously at an angle of 0º was identified with the low-field limit of the twin-plane activity.

Effect of Twin Planes on the Magnetization Hysteresis Loops of NdBa2Cu3O7 Single Crystals. M.Jirsa, M.R.Koblischka, T.Higuchi, M.Murakami: Physical Review B, 1998, 58[22], R14771-4