Vibrating-reed experiments on superconducting suspensions

Abstract
The frequency of a vibrating reed made of a superconducting suspension of isolated micrometer-size grains of low- and high-Tc superconductors in a magnetic field directly measures the elastic pinning force on the flux line. Four different types of field and temperature dependences of the attenuation caused by moving flux lines are observed and explained. In particular, the shift to lower temperatures of the dissipation peak of small high-Tc grains perfectly agrees with the prediction by thermally activated depinning.