  The effect of optical pumping and applied magnetic field on the
characteristics of ferromagnetic layers in one-dimensional superlattices is
studied. At low enough temperatures, these layers correspond to phase
separation domains in RMn_2O_5 and R_{0.8}Ce_{0.2}Mn_2O_5 multiferroics. The
formation of such domains occurs owing to the charge ordering of Mn^{3+} and
Mn^{4+} ions and to the finite probability for e_g electrons to tunnel between
these pairs of ions. The volume occupied by such superlattices is rather small,
and they can be treated as isolated ferromagnetic semiconductor
heterostructures, spontaneously formed in the host crystal. The sequences of
ferromagnetic resonances related to the superlattice layers in
Eu_{0.8}Ce_{0.2}Mn_2O_5 are studied. The characteristics of these resonances
give information on the properties of such layers. For the first time, it is
demonstrated that the optical pumping gives rise to a new metastable state of
superlattices, which can be recovered by the magnetic field cycling to the
state existing before the optical pumping. It is found that the superlattices
recovered by the magnetic field exist up to temperatures higher than those in
as-grown crystals.
