  Equilibrium spin configurations and their stability limits have been
calculated for models of magnetic superlattices with a finite number of thin
ferromagnetic layers coupled antiferromagnetically through (non-magnetic)
spacers as Fe/Cr and Co/Ru multilayers. Depending on values of applied magnetic
field and unaxial anisotropy, the system assumes collinear(antiferromagnetic,
ferromagnetic, various "ferrimagnetic") phases, or spatially inhomogeneous
(symmetric spin-flop phase and asymmetric, canted and twisted, phases)via
series of field induced continuous and discontinuous transitions. Contrary to
semi-infinite systems a surface phase transition, so-called "surface
spin-flop", does not occur in the models with a finite number of layers. It is
shown that "discrete jumps" observed in some Fe/Cr superlattices and
interpreted as "surface spin-flop" transition are first-order "volume"
transitions between different canted phases. Depending on the system several of
these collinear and canted phases can exist as metastable states in broad
ranges of the magnetic fields, which may cause severe hysteresis effects. The
results explain magnetization processes in recent experiments on
antiferromagnetic Fe/Cr superlattices.
