Amplitude-dependent damping of axial-torsional oscillations of a cylinder of the alloy Al--13.5 at.% Ag

The damping of oscillations of cylinders made of the superconducting alloy Al--13.5 at.% Ag was investigated. It was established that under different heat treatment a defect structure consisting of spherical Guinier--Preston zones and individual γ'-phase lamellae was formed in one specimen while in another specimen it was an ordered structure of γ'-phase lamellae along with the equilibrium γ-phase. With a decrease in the amplitude of the oscillations in magnetic fields relatively far from the lower critical field, the damping at first increases, reaches a maximum, and then decreases as the amplitude continues to decrease. With the growth of the magnetic field the damping maximum shifts to lower amplitudes. The concentration C/sub p/ of pinned fluxoids (in relation to the total number of fluxoids in the specimen) was found from the magnetization curves and from data on the oscillation frequency of the specimen. It was discovered that in each case the damping maximum is observed at C/sub p/approx.0.5, i.e., when roughly half of the fluxoids are pinned and the other half are free