FLUX-LINE MATCHING EFFECTS IN YBA2CU3O7-X THIN-FILMS

We present internal friction (IF) measurements in magnetic fields up to 1.6 T of epitaxial YBa2Cu3O7-x, thin films with different thicknesses. Measurements at constant temperature and varying field exhibit peaks in the IF at particular values of the field for H perpendicular to the crystallographic c axis. Assuming a rectangular flux line arrangement and taking the anisotropy of YBa2Cu3O7-x into account the positions of the peaks coincide with fields where the distance in c direction of the flux line rows becomes an integral fraction of the sample thickness. This matching effect is valid for different film thicknesses and seems to be independent of temperature.