DAMPING OF THE OSCILLATIONS OF A PERMANENT-MAGNET LEVITATING BETWEEN HIGH-T-C SUPERCONDUCTORS

A permanent magnet (spherical shape, radius 100 mu m) is levitating in side a superconducting parallel plate capacitor made of YBCO. Translat ional oscillations of the magnet at its resonance frequency (similar t o 150 Hz) can be excited and detected. The damping of the oscillations is investigated as a function of temperature and oscillation amplitud e. Close to T-c we observe a steep minimum of the damping. The data ca n be described by a linear frictional force which decreases near T-c, and a quadratic one which diverges at T-c. These frictional forces are attributed to flux flow phenomena in the high-T-c superconductor. (C) 1995 American Institute of Physics.