  A layered antiferromagnetic superconductor in the mixed state may posses
magnetic domains created along the Josephson vortices. This may happen when an
external magnetic field is strong enough to flip over magnetic moments, lying
in the phase core of the Josephson vortex, from their ground state
configuration. The formation of the domain structure of the vortices modifies
the surface energy barrier of the superconductor. During this process the
entrance of the flux is stopped and a newly created state exhibits perfect
shielding. Such behavior should be visible as a plateau on the dependence of
flux density as a function of the external magnetic field. The end of the
plateau determines the critical field, which we call the second critical field
for flux penetration.
