Electromagnons in the multiferroic state of perovskite manganites with symmetric exchange striction

We have investigated electrically active magnetic excitations (electromagnons) in perovskite manganites with the $E$-type (up-up-down-down) spin structure by terahertz spectroscopy. ${\text{Eu}}_{1\ensuremath{-}x}{\text{Y}}_{x}{\text{MnO}}_{3}$ $(0.1\ensuremath{\le}x\ensuremath{\le}1)$ and ${\text{Y}}_{1\ensuremath{-}y}{\text{Lu}}_{y}{\text{MnO}}_{3}$ $(0\ensuremath{\le}y\ensuremath{\le}1)$ without magnetic $f$ moments, which host collinear sinusoidal, $A$-type, cycloidal, and $E$-type spin orders, are used to examine the systematics of possible electromagnons. Three-peak structures (2.8, 4.3, and 5.6 meV) of magnetic origin show up in the $E$-type phase with little composition $(y)$ dependence of frequencies, making a contrast with the electromagnons observed in the cycloidal-spin $(x\ensuremath{\le}0.8)$ phases. One of these electromagnon is ascribed to the zone-edge magnon mode based on the calculated magnon dispersions.