Surface pinning in an amorphous ZrTiCuNiBe alloy

We have measured the amplitude and the phase of an electromagnetic (EM) field radiated from a superconductor (amorphous ZrTiCuNiBe alloy) in the mixed state due to the interaction of the flux lattice with an elastic wave. The results point to an essential contribution of a surface pinning into the flux lattice dynamics. We propose a model that describes radiation of the EM field from superconductors with nonuniform pinning. The model allows us to reconstruct the viscosity and the Labusch parameters from the experimental data. The behavior of the Labusch parameter can be qualitatively explained in terms of the collective pinning theory with the allowance of thermal fluctuations.