Drastic increases of frequency and damping of a superconducting vibrating reed in a longitudinal magnetic field

Drastic increases of resonance frequency (factor of 7) and damping (factor of >500) of a superconducting reed is observed when a longitudinal magnetic field is applied. The frequency change is much larger than expected from the pole effect (10⁵ times) or from the flux-line-tilt modulus (20 times). We give a quantitative explanation with no adjustable parameter. Unpinning of flux lines leads to frequency corrections and to damping. This allows novel precision measurements of extremely weak pinning in amorphous alloys. First experiments demonstrate the feasibility of this method.