MAGNETIC-RELAXATION AND PINNING POTENTIAL IN SUPERCONDUCTING RB3C60 POWDER

Magnetic relaxation in various magnetic fields and at different temper atures was carried out in Rb3C60 powder with T-C = 30.5 K, and its pin ning potential as functions of temperature and field is determined fro m these relaxation measurements. For H = 5 kOe, the apparent pinning p otential, U-O, is 12 meV at 5 K, and increases to about 47 meV with te mperature up to 12.5 K. Then it keeps at 45 meV between T = 12.5 K and 20 K, and at last decreases with temperature. For 3 kOe, a maximum U- O of 35 meV was observed at T = 20 K. At T = 15 K, the U-O rapidly dec reases from similar to 60 meV to 24 meV as field increases from 1 kOe to 2 kOe, then it shows field-independent and always remains at 24 meV in our measuring field range.