https://scholar.dgist.ac.kr/handle/20.500.11750/39 Tue, 21 Jul 2026 19:55:49 GMT 2026-07-21T19:55:49Z https://scholar.dgist.ac.kr/handle/20.500.11750/60458 Title: Magnetic glass behaviors of bicontinuous nanocomposite films fabricated by partial oxidation of Pt-Ni-Co Author(s): Ha, Jae-Hyun; Cho, Beopgil; Park, Jaemun; Kim, Tae-Hwan; Park, Keeseong; Han, Dong-Soo; Hong, Jung-Il Abstract: We report the magnetic properties of metal/oxide hybrid nanocomposite thin films derived from an interpenetrating nanoscale morphology formed by reactive co-sputtering of Pt and Co0.7Ni0.3 in a controlled argon and oxygen atmosphere at room temperature. During deposition, selective oxidation of transition-metal elements of Co and Ni, in the presence of less reactive Pt, drives spontaneous phase separation into ferromagnetic (FM) metallic PtNi and antiferromagnetic (AFM) amorphous CoO nanophases. The resulting nanocomposite constitutes a highly entangled three-dimensional network of FM/AFM domains where characteristic dimensions remain in the order of approximately less than 2 nm. The resulting bicontinuous architecture facilitates dense interfacial spin couplings across the entire volume of the film. Unlike conventional exchange-biased magnetic multilayer systems, the nanocomposite exhibits markedly slow spin dynamics near the magnetic transition region, as evidenced by strong frequency dependence of AC susceptibility. This behavior is attributed to the complex magnetic energy landscape caused by the disordered distribution of AFM regions surrounding the FM phase. At lower temperatures below the blocking point, the FM PtNi phase becomes strongly exchange-coupled with the adjacent AFM CoO, leading to a magnetically frozen state. These observations indicate a re-entrant magnetic glass behavior originated from the nanoscale interfacial frustration in the spontaneously formed multiple magnetic nanophases. Thu, 30 Apr 2026 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/60458 2026-04-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60020 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. Sat, 31 Jan 2026 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/60020 2026-01-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58559 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. Mon, 30 Jun 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/58559 2025-06-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58274 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. Sun, 31 Aug 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/58274 2025-08-31T15:00:00Z