Sae Hwan Chun, Kwang Woo Shin, Hyung Joon Kim, Seonghoon Jung, Jaehun Park, Young Mi Bahk, Hyeong Ryeol Park, Ji Soo Kyoung, Da-Hye Choi, Dae-Sik Kim, Gun-Sik Park, John F. Mitchell, and Kee Hoon Kim
https://journals.aps.org/prl/accepted/d0079Y40Oe81095739b74618cf6352f7426e0ff08
An electromagnon in the magnetoelectric (ME) hexaferrite Ba0.5Sr2.5Co2Fe24 O41 (Co2Z-type) single crystal is identified by time-domain terahertz (THz) spectroscopy. The associated THz resonance is active on electric field (E\omega ) of the THz light parallel to the c axis (\textbar \textbar [001]), whose spectral weight develops at a markedly high temperature, coinciding with a transverse conical magnetic order below 410 K. The resonance frequency of 1.03 THz at 20 K changes -8.7 {\%} and +5.8 {\%} under external magnetic field (H) of 2 kOe along [001] and [120], respectively. A model Hamiltonian describing the conical magnetic order elucidates that the dynamical ME effect arises from anti-phase motion of spins which are coupled with modulating electric dipoles through exchange striction mechanism. Moreover, the calculated frequency shift points to the key role of Dzyaloshinskii-Moriya interaction that is altered by static electric polarization change under different H.
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