Internal Friction of Flux Motion in Hg-System High-T_c Superconductors

Abstract
The internal friction(IF) and modulus as functions of temperature were measured for several Hg-system high-Tc superconductors(Hg1201, Hg1223, Hg1223 doped with Fe and Pb), under the applied magnetic field, with vibrating reed technique. An IF peak associated with flux motion can be found below Tc for all samples. The temperature of the IF peak increases with reducing vibrating amplitude. This amplitude dependence of IF indicates that the flux motion is characterized by nonlinear behavior. No apparent shift of IF peak position can be detected by varying the frequency in the range from 10²Hz to 10³ Hz. Furthermore, the IF peak height satisfies a scaling law Q^-1 α ω^-n. This may be originated from phase transition of flux line lattice(FLL) rather than a thermally activated diffusion process.