Received 30 March 2013; published 17 July 2013
Both electric- and magnetic-dipole active spin excitations, i.e., electromagnons, which mediate the dynamical magnetoelectric effect, have been investigated for a multiferroic perovskite of manganite by optical spectroscopy at terahertz frequencies. Upon the magnetoelectric resonance at 1 meV in the multiferroic phase with the bc-plane spin cycloidal order, a gigantic dynamical magnetoelectric effect has been observed as a nonreciprocal directional dichroism or birefringence. The light k-vector-dependent difference (Δκ=κ+-κ-) of the extinction coefficient (κ±) is as large as Δκ∼1 or 2Δκ/(κ++κ-)∼0.7 at the lowest-lying electromagnon energy. We clarified the mutual coupling of theEω∥a-polarized electromagnons of the different origins, leading to the enhancement of the magnetoelectric resonance.
© 2013 American Physical Society
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