Magnetic field gain in vortex pinning at fractal interfaces of clusters of high-temperature superconductors

The effect of the fractality of the cluster interfaces in the normal phase of a copper-oxide high-temperature superconductor YBCO on the magnetic creep has been studied. The model of a magnetic field dependence of voltage induced by the flux creep for different transport currents has been suggested. The experimental dependences have been approximated using an exponent-hyperbolic function with a current parameter. The empiric magnetic field dependence of the fractal dimensionality of the interfaces of YBCO clusters has been registered. The magnitudes of the magnetic field intensity and fractal dimensionality at which the vortices start to penetrate the granules of the samples have been determined. The connective index of paths of the vortex quench at the percolation threshold has been calculated.