Abstract-Electromagnon with Sensitive Terahertz Magnetochromism in a Room-Temperature Magnetoelectric Hexaferrite

Sae Hwan Chun, Kwang Woo Shin, Hyung Joon Kim, Seonghoon Jung, Jaehun Park, Young-Mi Bahk, Hyeong-Ryeol Park, Jisoo Kyoung, Da-Hye Choi, Dai-Sik Kim, Gun-Sik Park, J. F. Mitchell, and Kee Hoon Kim

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.027202

An electromagnon in the magnetoelectric (ME) hexaferrite ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{2.5}{\mathrm{Co}}_2{\mathrm{Fe}}_{24}{O}_{41}$ (${\mathrm{Co}}_{2}Z$-type) single crystal is identified by time-domain terahertz (THz) spectroscopy. The associated THz resonance is active on the electric field ($E^{\omega }$) of the THz light parallel to the $c$ axis ($\parallel \left[001\right]$), 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 antiphase motion of spins which are coupled with modulating electric dipoles through the exchange striction mechanism. Moreover, the calculated frequency shift points to the key role of the Dzyaloshinskii-Moriya interaction that is altered by static electric polarization change under different $H$.

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Abstract-Electromagnon with sensitive terahertz magnetochromism in a room-temperature magnetoelectric hexaferrite

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.

Abstract-Optical Properties of Tetrahydrofuran Clathrate Hydrates with Polyvinylpyrrolidone (THF + H2O + PVP) Revealed by Terahertz (THz) Time-Domain Spectroscopy

Hyery Kang †, Dong-Yeun Koh †, Yun-Ho Ahn †, Seonghoon Jung §, Jaehun Park §, Jaehyoung Lee*∥, and Huen Lee *†‡

† Department of Chemical and Biomolecular Engineering (BK21+ program), KAIST, Daejeon 305-701, Republic of Korea

‡ Graduate School of EEWS, KAIST, Daejeon 305-701, Republic of Korea

§ Pohang Accelerator Laboratory, POSTECH, Pohang 790-784, Republic of Korea

∥ Petroleum & Marine Research Division, Korea Institute of Geoscience & Mineral Resources, Gwahang-no 92, 30, Yuseong-gu, Daejeon 305-350, Republic of Korea

J. Chem. Eng. Data, Article ASAP

DOI: 10.1021/je5005092

Publication Date (Web): October 29, 2014

Copyright © 2014 American Chemical Society

*(H.L.) E-mail: hlee@kaist.ac.kr., *(J.L.) E-mail: ljh1155@kigam.re.kr

http://pubs.acs.org/doi/abs/10.1021/je5005092

Terahertz time-domain spectroscopy (THz-TDS) was used to observe the tetrahydrofuran (THF) clathrate hydrate system with dosage of polyvinylpyrrolidone (PVP) with three different average molecular weights (10 000 g/mol, 40 000 g/mol, and 360 000 g/mol). Distinct footprints of phase transition in the THz region (0.4 THz to 2.2 THz) were analyzed and absorption coefficients and complex refractive indices are obtained and compared in the temperature range of 253 to 288 K. Along with the optical properties, ring breathing and stretching modes for different molecular weights of PVP in THF hydrate are analyzed by Raman spectroscopy.