Columnar defects acting as passive internal field detectors

We have studied the angular dependence of the irreversible magnetization of several YBa₂Cu₃O₇ and 2H-NbSe₂ single crystals with columnar defects tilted off the c axis. At high magnetic fields, the irreversible magnetization Mᵢ(Θ) exhibits a well-known maximum when the applied field is parallel to the tracks. As the field is decreased below H~0.02Hc2, the peak shifts away from the tracks' direction toward either the c axis or the ab planes. We demonstrate that this shift results from the misalignment between the external and internal field directions due to the competition between anisotropy and geometry effects.