Effect of the optical pumping and magnetic field on the states of phase separation domains in Eu$_{0.8}$Ce$_{0.2}$Mn$_2$O$_5$

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$_2$O$_5$ and R$_{0.8}$Ce$_{0.2}$Mn$_2$O$_5$ 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$_2$O$_5$ 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.