VORTEX BENDING IN A TILTED YBA2CU3O7-DELTA CRYSTAL

Magnetization-vector measurements were made on a YBa2Cu3O7-delta cryst al, initially cooled to 4.2 K in an external field H-e parallel to the c axis. With H-e fixed, the crystal was then tilted, such that the an gle theta between the c axis and H-e was gradually raised to 90 degree s and lowered back to zero. Our results reveal that all the vortex flu x remains parallel to the c axis until the tilt angle theta reaches a threshold value (close to 15 degrees for H-e less than or equal to 500 Oe). As theta exceeds this value, the vortex flux in the ab plane ris es rapidly from zero, and it appears to derive solely from a bending o f the vortices initially directed along c. This whole process is fairl y consistent with theoretical predictions, and it is found to be essen tially reversible with the cycling of theta at low H-e. The hysteresis that develops at higher H-e rises and approaches the conventional hys teresis measured along ab after zero-field cooling. Comparison is also made with a cross-flux experiment, which is seen to be only superfici ally equivalent to the crystal-tilt experiment.