We have measured the irreversible magnetization $\left({\mathbf{M}}_i\right)$ of an ${\mathrm{ErBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ single crystal with columnar defects (CD), using a technique based on sample rotation under a fixed magnetic field H. This method is valid for samples whose magnetization vector remains perpendicular to the sample surface over a wide angle range—which is the case for platelets and thin films—and presents several advantages over measurements of ${\mathbf{M}}_L\mathrm{}\left(H\right)\mathrm{}$ loops at fixed angles. The resulting ${\mathbf{M}}_i\left(\Theta \right)$ curves for several temperatures show a peak in the CD direction at high fields. At lower fields, a very well defined plateau indicative of the vortex lock-in to the CD develops. The H dependence of the lock-in angle ${\phi }_L$ follows the $H^{-1}$ theoretical prediction, while the temperature dependence is in agreement with entropic smearing effects corresponding to long range vortex-defects interactions.

• Received 4 March 2001

DOI:https://doi.org/10.1103/PhysRevB.64.144502