Numerical studies on the effect of normal-metal coatings on the magnetization characteristics of type-II superconductors

Magnetic properties of superconductors coated with metals of arbitrary\udresistivity rho(N) are calculated using the time-dependent\udGinzburg-Landau equations in which both T-c and rho(N) vary. As rho(N)\udin the coating is reduced, the initial vortex penetration field\udH-p(rho(N)) does not decrease monotonically from the insulating\ud(Matricon) limit to the extreme metallic (Bean-Livingston) limit, but\udhas a minimum value H-p(min) below the extreme metallic value. The\udminimum occurs because the barrier is weakened by proximity-effect\udpenetration of superelectrons into the coating which only occurs at\udfinite resistivity. In an applied magnetic field, local depressions in\udpsi nucleate in the coating which do not have the well-known quantum of\udmagnetic flux (h/2e) until they have crossed the coating and entered\udthe interior of the superconductor. When T=0 and T-c of the normal\udmetal coating is zero, the minimum vortex penetration field\udH(p(min))approximate to 0.76 kappa(-1.17)H(c2) which occurs for a\udcoating resistivity rho(N)approximate to 1.1 kappa(-0.6)rho(S). For T>0\udthe minimum is attenuated. Adding a thick weakly superconducting S'\udlayer between the superconductor and normal metal coating reduces the\udirreversibility markedly