Abstract-Direct observation of terahertz emission from ultrafast spin dynamics in thick ferromagnetic films

Applied Physics Letters

 Lin Huang, Ji-Wan Kim,  Sang-Hyuk Lee, Seon-Dae Kim,  Van Manh Tien,  Kiran Prakash Shinde, Je-Ho Shim, Yooleemi Shin, Hee Jun Shin, Seongheun Kim, Jaehun Park, Seung-Young Park, Yeon Suk Choi, Hyun-Joong Kim,  Jung-Il Hong,  Dong Eon Kim, Dong-Hyun Kim

Schematic diagram of THz emission and detection by the electro-optic (EO) sampling method. The dotted box area is zoomed to show the sample region with the axis configuration.

https://aip.scitation.org/doi/abs/10.1063/1.5087236

We have experimentally investigated the field- and fluence-dependent terahertz (THz) emission behaviors by a femtosecond optical pump in Co ferromagnetic films, together with the time-resolved magneto-optical Kerr effect measurement. The thickness of Co and Ta capping layers has been systematically varied. For thick films, THz emission behavior is found to be directly matched with the photoinduced ultrafast demagnetization and remagnetization dynamics. The angle-dependent THz emission measurement also confirms a direct relation between the THz emission and the photoinduced demagnetization/remagnetization dynamics in the case of thick films, while THz emission from the inverse spin Hall effect also plays a role in the case of thin Co films.

This work was supported by the Korea Research Foundation (NRF) (Grant Nos. 2018R1A2B3009569 and 2017R1A6A3A04011173) and by KBSI Grant No. D39614. This work was also supported in part by the Global Research Laboratory Program (Grant No. 2009-00439) and by the Max Planck POSTECH/KOREA Research Initiative Program (Grant No. 2016K1A4A4A01922028) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning.

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-Stabilization of radiation intensity at an electron-based THz radiation facility

Jun Ho Ko, In Soo Ko, Seong Hoon  Jung, Jaehun Park, Heung Sik Kang,

https://link.springer.com/article/10.3938/jkps.72.21

The femtosecond (fs) terahertz (THz) beamline of Pohang Accelerator Laboratory (PAL) is providing a THz radiation with the pulse energy of 7 μJ by means of coherent transition radiation (CTR) from a 65-MeV electron beam. The fs-THz beamline is dedicated to the user service operation for which we need to provide a stable radiation for beamline experiments. For this purpose, we have improved electron bunch length measurement and an RF phase feedback system for stabilizing the THz radiation intensity.

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.