ANGULAR-DEPENDENCE OF CREEP IN YBCO SINGLE-CRYSTALS INVESTIGATED BY TORQUE MAGNETOMETRY

Investigations by means of torque magnetometry at 77K reveal different torque contributions in YBCO single crystals due to intrinsic anisotropy as well as several types of crystal defects. The angular dependence of the irreversible part of the magnetization shows remarkable peculiarities in comparison with other HTSC materials. In contrast to earlier results with Bi- and Tl-type materials, scaling of the magnetization component parallel to the c-axis with the corresponding flux density component is only roughly fullfilled indicating deviations from twodimensionality in YBCO. Torque relaxation measurements reveal that, depending on the field orientation, different relaxation laws may occur. Effective pinning barriers extracted from the decay curves depend strongly on the field orientation. This dependence is clearly different from that found in BSCCO investigated previously. Results are discussed with respect to the ''butterfly'' shape observed commonly for magnetization curves of YBCO.