https://scholar.dgist.ac.kr/handle/20.500.11750/39 2026-04-04T14:57:50Z 2026-04-04T14:57:50Z Shim, Je-Ho Zhao, Yunxiu Mustaghfiroh, Qoimatul Thi, Nguyen Le Rahmani, Fathiya Kim, Kyungwan Shin, Hee Jun Park, Jaehun You, Xiao Wan, Caihua Jung, Min-Seung Hong, Jung-Il Han, Xiufeng Piao, Hong-Guang Kim, Dong-Hyun https://scholar.dgist.ac.kr/handle/20.500.11750/60020 2026-02-10T09:10:19Z 2026-01-31T15:00:00Z

Title: Terahertz Emission Modulation Caused by Ultrafast Breaking and Recovery of Exchange Bias Author(s): Shim, Je-Ho; Zhao, Yunxiu; Mustaghfiroh, Qoimatul; Thi, Nguyen Le; Rahmani, Fathiya; Kim, Kyungwan; Shin, Hee Jun; Park, Jaehun; You, Xiao; Wan, Caihua; Jung, Min-Seung; Hong, Jung-Il; Han, Xiufeng; Piao, Hong-Guang; Kim, Dong-Hyun Abstract: Magnetic interfacial exchange bias, as a key control method for spintronic devices, remains unclear in terms of its ultrafast dynamic behavior and its role in regulating spintronic terahertz emissions. In this work, femtosecond optical pulses are used to excite ferromagnetic/antiferromagnetic bilayer films with interfacial exchange bias, and a significant modulation phenomenon of terahertz emission is observed by comparing samples with different magnetization pinning states induced by exchange bias. Through the measurement of dynamic hysteresis loops under femtosecond optical pulse excitation, it is confirmed that the optical pulse can rapidly break and then recover the exchange bias within the picosecond time scale. This transient reconstruction process of exchange bias effectively enhances the ultrafast spin precession signal at approximate to 2 THz, while suppressing the ultrafast demagnetization-related signal at approximate to 0.77 THz. By exploiting the difference in flip symmetry of the samples, this is found that the photo-introduced magnetization dynamics process dominated the modulation effect of the exchange bias on the two frequency bands. These results reveal that picosecond-scale transient exchange bias can regulate both the frequency content and coherence of spintronic terahertz emission, offering a pathway toward tunable terahertz spintronic sources.

2026-01-31T15:00:00Z Choi, Won-Young Ha, Jae-Hyun Jung, Min-Seung Kim, Seong Beom Koo, Hyun Cheol Lee, OukJae Min, Young-Chul Jang, Hyejin Shahee, Aga Kim, Ji-Wan Klaui, Mathias Hong, Jung-Il Kim, Kyoung-Whan Han, Dong-Soo https://scholar.dgist.ac.kr/handle/20.500.11750/58559 2025-12-18T18:01:14Z 2025-06-30T15:00:00Z

Title: Magnetization switching driven by magnonic spin dissipation Author(s): Choi, Won-Young; Ha, Jae-Hyun; Jung, Min-Seung; Kim, Seong Beom; Koo, Hyun Cheol; Lee, OukJae; Min, Young-Chul; Jang, Hyejin; Shahee, Aga; Kim, Ji-Wan; Klaui, Mathias; Hong, Jung-Il; Kim, Kyoung-Whan; Han, Dong-Soo Abstract: Efficient control of magnetization in ferromagnets is crucial for high-performance spintronic devices. Magnons offer a promising route to achieve this objective with reduced Joule heating and minimized power consumption. While most research focuses on optimizing magnon transport with minimal dissipation, we present an unconventional approach that exploits magnon dissipation for magnetization control, rather than mitigating it. By combining a single ferromagnetic metal with an antiferromagnetic insulator that breaks symmetry in spin transport across the layers while preserving the symmetry in charge transport, we realize considerable spin-orbit torques comparable to those found in non-magnetic metals, enough for magnetization switching. Our systematic experiments and comprehensive analysis confirm that our findings are a result of magnonic spin dissipation, rather than external spin sources. These results provide insights into the experimentally challenging field of intrinsic spin currents in ferromagnets, and open up possibilities for developing energy-efficient devices based on magnon dissipation.

2025-06-30T15:00:00Z Park, Kwon-Jin Cho, Jaeyong Lee, Soobeom Cho, Jaehun Ha, Jae-Hyun Jung, Jinyong Kim, Dongryul Choi, Won-Chang Hong, Jung-Il You, Chun-Yeol https://scholar.dgist.ac.kr/handle/20.500.11750/58274 2025-10-17T01:40:16Z 2025-08-31T15:00:00Z

Title: Control of Ferromagnetism of Vanadium Oxide Thin Films by Oxidation States Author(s): Park, Kwon-Jin; Cho, Jaeyong; Lee, Soobeom; Cho, Jaehun; Ha, Jae-Hyun; Jung, Jinyong; Kim, Dongryul; Choi, Won-Chang; Hong, Jung-Il; You, Chun-Yeol Abstract: Vanadium oxide (VOx) is a material of significant interest due to its metal-insulator transition (MIT) properties as well as its diverse stable antiferromagnetism depending on the valence states of V and O with distinct MIT transitions and N & eacute;el temperatures. Although several studies reported ferromagnetism in the VOx, it is mostly associated with impurities or defects, and pure VOx has rarely been reported as ferromagnetic. The research presents clear evidence of ferromagnetism in the VOx thin films, exhibiting a saturation magnetization of approximate to 13 kA m-1 at 300 K. The 20-nm thick VOx thin films via reactive sputtering from a metallic vanadium target in various oxygen atmospheres is fabricated. The oxidation states of ferromagnetic VOx films show an ill-defined stoichiometry of V2O3+p, where p = 0.05, 0.23, 0.49, with predominantly disordered microstructures. The ferromagnetic nature of these VOx films is confirmed through a strong antiferromagnetic exchange coupling with the neighboring ferromagnetic layer in the VOx/Co bilayers, in which the spin configurations of the Co layer is influenced strongly due to the additional anisotropy introduced by VOx layer. The present study highlights the potential of VOx as an emerging functional magnetic material with tunability by oxidation states for modern spintronic applications.

2025-08-31T15:00:00Z Nguyen, Thanh-Huong Thi Park, Jungmin Ha, Jae-Hyun Lee, Soogil Nguyen, Van Quang Lee, Nyun Jong Park, Byong-Guk Cho, Sunglae Hong, Jung-Il Kim, Sanghoon https://scholar.dgist.ac.kr/handle/20.500.11750/57056 2025-07-25T03:25:54Z 2024-03-31T15:00:00Z

Title: Giant anisotropy of magnetic damping in an epitaxial Cr/Fe bilayer with the absence of magnetocrystalline anisotropy Author(s): Nguyen, Thanh-Huong Thi; Park, Jungmin; Ha, Jae-Hyun; Lee, Soogil; Nguyen, Van Quang; Lee, Nyun Jong; Park, Byong-Guk; Cho, Sunglae; Hong, Jung-Il; Kim, Sanghoon Abstract: Magnetic damping is one of the most important parameters governing the critical current density for current-induced magnetization switching in spin-torque devices. The anisotropic nature of magnetic damping, influenced by both intrinsic and extrinsic factors, has been demonstrated in both theoretical and experimental studies. Nevertheless, understanding the underlying mechanisms of magnetic damping anisotropy, particularly in the bilayer structure of a ferromagnet and a nonmagnetic metal, remains an open challenge. In this study, we investigate the crystallographic dependence of magnetic damping in an epitaxial Cr/Fe bilayer, which has negligible magnetocrystalline anisotropy. We experimentally extracted the total damping by conducting frequency-dependent ferromagnetic resonance measurement at different in-plane angles. The observed damping reveals a strong angular dependence with an anisotropy of similar to 400% in the bilayer. All possible contributions to the total damping will be discussed carefully to clarify the origin of the profound damping anisotropy observed in our Cr/Fe bilayer.

2024-03-31T15:00:00Z