Physical review b vol:60 issue:18 pages:13189-13195
We have studied the angular dependence of the irreversible magnetization and its time relaxation in YBa2Cu3O7 Single crystals with one or two families of columnar defects inclined with respect to the c axis. At high magnetic fields, the magnetization shows the usual maximum centered at the mean tracks' orientation and an associated minimum in the normalized relaxation rate. In contrast, at low fields we observe an anomalous local minimum in the magnetization and a maximum in the relaxation rate. We present a model to explain this anomaly based on the slowing down of the creep processes arising from the increase of the vortex-vortex interactions as the applied field is tilted away from the mean tracks' direction. [S0163-1829(99)11841-1].