Description of a new vibrating reed technique for the study of type II superconducting materials

A very sensitive apparatus using the vibrating reed technique in a magnetic field is described. This new technic is an internal friction measurement which has been developed and applied to the study of vortex pinning in high Tc type II superconductors. The vibrating reed is simply used as a sample holder for the superconductor which can be oriented thin films, bulk samples or powders. The salient feature of this experimental set-up is the excitation mode of the reed for which the imposed vibration frequency can be freely chosen in the range 10-4-10 Hz. Furthermore, the measurement sensitivity improves the performances obtained up to now by such similar apparatus as forced torsion pendulums. Damping values corresponding to phase lags between 10-5 and 10-4 radian can be readily obtained for vibration frequencies in the range 10-1 10 Hz. Some preliminary results show damping peaks which might be due to the so-called fusion of the vortex network obtained with thin films whose thickness is 1000 A and with textured bulk samples of YBaCuO. (orig.)