PINNING-FORCE SCALING AND MAGNETIC-RELAXATION IN DOPED Y-BA-CU-O THIN-FILMS

The flux-pinning-force density F(p) and apparent pinning potential U(0) in a series of 3d-transition-metal (Fe, Co, and Ni) -doped Y-Ba-Cu-O thin films have been measured as a function of magnetic field, temperature, and doping concentration. F(p) shows an interesting double-peak behavior with an additional critical field H* separating the peaks. It is believed that this feature is associated with the flux-line configuration in the thin film in a transverse field. A universal scaling law can be applied which accounts for all the variations with field, temperature, and doping concentration. The magnetic-relaxation measurements of U(0) show that the thermally activated flux creeps are enhanced in these doped films. The variation of U(0) and VX as a function of field and temperature are consistent with the F(p) characteristic which can be described by the flux-creep model in the critical state. (Here V and X are, respectively, the activation volume and the width of the pinning barrier.)