Magneto-optical observation of dynamic relaxation in YBa₂Cu₃O_7-δ thin films

Using magneto-optical visualization of the flux in superconductors, the dependence of the flux distributions on the rate of sweep of the external magnetic field dH_cxt/dt ('dynamic relaxation') is directly observed for YBa₂Cu₃O_7-δ thin films patterned into small rectangles. The differences in the flux patterns are clearly detectable especially when the sample is not fully penetrated. Various ways of analysing the flux patterns in order to determine the dynamic relaxation rate Q quantitatively from the magneto-optical images are discussed.