Dynamic magnetic forces in superconducting ceramics

Abstract

Dynamic forces between small permanent magnets and bulk high-Tc superconducting ceramic materials have been measured, including magnetic stiffness and damping effects. The vibration frequencies and the related magnetic stiffness show a large dependence on the magnet-superconductor distance. The dynamic magnetic stiffness is shown to be related to small static reversible magnetic forces, but is not correlated with the static hysteretic forces. The magnetic damping is inversely related to the magnet-superconductor distance and can critically damp the oscillations at small gaps. These data also show that the flux pinning forces depend on the prior flux history in the superconductor.