Narrow dip in the angular dependence of the irreversible magnetic moment in columnar-defected YBa2Cu3Oy single crystals

When the magnetic field H is rotated around the axis parallel to the short side of columnar-defected YBa2Cu3Oy single crystals, we observe a narrow dip in the irreversible magnetic moment for H parallel to the columns. The conditions for the existence of this phenomenon have been clarified by investigating different sample geometries and field orientations. Using the anisotropic critical state model, we show that the anomaly arises from a sharp increase of the critical current density parallel to the field rotation plane. Possible explanations for the underlying vortex dynamics are discussed.