  The magnetic field distribution, the magnetic flux, and the free energy of an
Abrikosov vortex loop near a flat surface of type--II superconductors are
calculated in the London approximation. The shape of such a vortex line is a
semicircle of arbitrary radius. The interaction of the vortex half--ring and an
external homogeneous magnetic field applied along the surface is studied. The
magnitude of the energy barrier against the vortex expansion into
superconductor is found. The possibilities of formation of an equilibrium
vortex line determined by the structure of the applied magnetic field by
creating the expanding vortex loops near the surface of type--II superconductor
are discussed.
