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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 $30l~Tl~90\mathrm{K}.$ 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.

Induced current densities {ital j}{sub {ital s}}({ital T},{ital B}) were measured in a wide temperature (5 {le}{ital T}{le} 90 K) and field range (0 {le}{mu}{sub 0}{ital H}{sub {ital a}}{le}7 T) on single crystals of NdBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} using a superconducting quantum interference device magnetometer. The samples exhibit the fishtail or peak effect at temperatures above 30 K. In a small temperature window between 50 and 74 K, three peaks are seen in the {ital j}{sub {ital s}}({ital T},{mu}{sub 0}{ital H}{sub {ital a}}) curves. The temperature and field behavior of the induced current densities is analyzed using a model describing a magnetization curve as composed of two independent contributions at low and high fields. By means of this analysis, it is demonstrated that the third peak corresponds to the fishtail peak, whereas the position of the second peak is practically independent of temperature. It is shown that the appearance of the second peak is due to the large values of the position of the fishtail peak. {copyright} {ital 1996 The American Physical Society.}