Disappearance of Friction in a Levitated YBa sub 2 Cu sub 3 O sub 7--x Superconductor in a Variable Magnetic Field

Influence of an alternating magnetic field on the levitation behaviour of a high-T sub c YBa sub 2 Cu sub 3 O sub 7--x superconductor above a ring-shaped permanent magnet was examined. The transition from a plastic type of levitation to an elastic one, induced by alternating field component, was observed. The field frequency dependence of the relaxation time of the superconductor to a single equilibrium position was studied. An explanation of these effects based on the hysteretic behaviour of the superconductor was proposed. Graphs. 11 ref.--AA