Flux-flop in high temperature superconducting crystals with columnar defects

Measurements of magnetization curves of Y-Ba-Cu-O crystals with columnar defects reveal pronounced peaks around H=0 for applied fields not parallel to the defect direction. The magnitude and direction of the remanent magnetization are independent of the direction of the applied field for a large range of angles. We show that the unidirectional character of the defects induces, in the low field limit, a flux-flop from a direction determined by the field to the defect direction. Implications to planar pinning are discussed.