  Ferromagnetic substrate influences the electromagnetic response of a type-II
superconducting film to the applied magnetic field. We present a
two-dimensional integrodifferential model for the magnetization of a flat
superconductor/ferromagnet bilayer of an arbitrary shape using a thin shell
quasistatic model for the ferromagnetic substrate and an infinitely thin
approximation for the superconducting layer. An efficient numerical method is
developed and used to investigate the effect of a ferromagnetic substrate. In
particular, we simulate the thin bilayer magnetization in a parallel field and,
for a high field, the critical-state distributions of the superconducting
current density. These critical-state distributions are different from those
known for a normal external field.
