Magnetic and magneto-lattice dynamics in GdMn$_2$O$_5$

The dynamics of magnetoelectric RMn$_2$O$_5$ crystals (R=Eu and Gd) was studied in the frequency and temperature ranges 20-300 GHz and 5-50 K, respectively. The crystals possessed magnetic and ferroelectric long-range order and had close transition temperatures, $T_{N.C.}\simeq 36$ and 30  K for R=Eu and Gd, respectively. Mixed magneto-lattice excitations were observed in GdMn$_2$O$_5$; the excitations were most intense near the transition temperature $T\simeq 30$  K at frequencies close to the antiferromagnetic resonance frequencies of the Mn-subsystem. Along with the antiferromagnetic resonance of the Mn-subsystem, the ferromagnetic resonance of the Gd-subsystem was observed in GdMn$_2$O$_5$ in an external magnetic field. No such dynamics was characteristic of EuMn$_2$O$_5$.