  In magnetic fields applied within the angular range of the surface
superconductivity state a magnetically anisotropic layered medium is created in
structurally isotropic, sufficiently thick niobium films. Surface (Kulik)
vortices residing in the superconducting sheaths on both main film surfaces in
tilted fields are shown to undergo a decoupling transition from a coherent to
an independent behavior, similar to the behavior observed for Giaever
transformer. At the transition a feature in pinning properties is measured,
which implies different pinning for the lattice of surface vortices coherently
coupled through the normal layer and for two decoupled vortex arrays in the
superconducting surface sheaths.
