https://scholar.dgist.ac.kr/handle/20.500.11750/813 2026-08-23T23:06:32Z https://scholar.dgist.ac.kr/handle/20.500.11750/60616 Title: Strong Enhancement of Room Temperature Ferrimagnetism in Insulating CoFe2O4 by Site-Specific Hydrogen Intercalation Author(s): Park, Jaewoo; Ha, Youngkyoung; Lee, Shinbuhm Abstract: Strong enhancement of magnetization is highly desirable for increasing device efficiency, improving temperature stability, enhancing sensitivity, and enabling device miniaturization. Here, we demonstrate a 2.6-4.7 times higher room temperature ferrimagnetic moment (730-770 emu cc-1) compared to 170-260 emu cc-1 in as-grown CoFe2O4 films, achieved by site-specifically intercalating hydrogen ions near the Fe3+ in tetrahedral sites. While the spin moments of the Fe3 + at octahedral and tetrahedral sites cancel each other out in as-grown films, X-ray spectroscopy of hydrogenated films reveals that both Fe3+ and Co2+ at octahedral sites can contribute to the enhanced total magnetic moment. This robust enhancement in insulating CoFe2O4, exhibiting high reproducibility over approximate to 10 cycles and long-term stability over approximate to 10 d, suggests that hydrogenic-ferrimagnetic coupling holds great promise for ultralow power electronics operating at high frequencies. 2026-07-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60218 Title: A Hidden Photoinduced Phase-Transition Pathway in Strain-Engineered VO2 Author(s): Park, Soon Hee; Park, Jaeku; Kim, Hyeong-Do; Choi, Songhee; Lee, Shinbuhm; Kim, Jong-Woo; Cho, Byeong-Gwan; Koo, Tae-Young; Eom, Intae; Kim, Minseok; Jang, Dogeun; Choi, Hyeongi; Park, Gwangryeol; Kim, Kyung Sook; Park, Sang-Youn; Shin, Hee Jun; Chae, Bok Nam; Park, Jaehun; Chun, Sae Hwan Abstract: Photoexcitation provides a versatile route to drive quantum materials into nonequilibrium states, opening opportunities for phase engineering beyond conventional tuning parameters such as temperature, magnetic field, pressure, or chemical doping/substitution. VO2, a prototypical correlated oxide, has long served as a model system for understanding photoinduced insulator-metal transitions, yet the sequence of structural and electronic transitions remains intensely debated. Here, we uncover a hidden photoinduced transition pathway in epitaxially strained VO2 thin films, in which the structural transition precedes the electronic insulator-metal transition, reversing the canonical temporal order. Femtosecond X-ray diffraction reveals a transient structural state characterized by the disappearance of vanadium dimers generating dynamic tensile strain, while time-resolved terahertz spectroscopy shows that the electronic gap closes only after the strain relaxation. This lattice-driven transition highlights the pivotal role of Mott correlations in dictating electronic properties under nonequilibrium conditions. Our findings establish strain-light coupling as a design principle for ultrafast control of phase transitions, offering new avenues for reconfigurable electronic and photonic devices based on correlated oxides. 2026-01-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60031 Title: Achieving wide-range steep slopes in SnS2 negative capacitance transistors through an isolated band structure and thermionic emission enhancement via Bi contacts Author(s): Song, Chong-Myeong; Park, Jaewoo; Lee, Shinbuhm; Kwon, Hyuk-Jun Abstract: Negative capacitance FETs aim for sub-60 mV dec-1 switching to curb power consumption, but often encounter instability and narrow steep-slope windows. We present a hysteresis-free NCFET that strategically utilizes a 2D SnS2 channel. The inherent isolated conduction band of SnS2, yielding a step-like density of states, is pivotal for sharp turn-on characteristics when effectively coupled with the negative capacitance effect. The SnS2 channel is integrated with an La:HfO2/HfO2 ferroelectric-dielectric gate stack and Bi contacts. This architecture shows an average subthreshold swing of 34 mV dec-1 across four current decades, maintaining sub-60 mV dec-1 operation over this wide range, and enabling sub-0.4 V operation. Bi contact is key, minimizing Fermi-level pinning at the SnS2/metal interface. This expands the thermionic emission region, allowing the negative capacitance to fully leverage the distinct properties of SnS2 for sustained wide-range steep-slope performance. This work demonstrates a novel approach to ultralow-power transistors by integrating an isolated-band semiconductor, optimized ferroelectric, and contact engineering. 2025-11-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59910 Title: Tunable Hydrogen Dynamics Under Electrical Bias for Neuromorphic Memory Applications Author(s): Noh, Hee Yeon; Lee, Chan-Kang; Haripriya, Gopalakrishnan Nair Ramani; Lee, Shinbuhm; Lee, Myoung-Jae; Wee, Jiyong; Lee, Hyeon-Jun Abstract: A wide variety of materials and device architectures have been explored for memristor applications targeting neural network simulations, most of which rely on oxide-based structures that exhibit resistive switching driven by oxygen-vacancy-mediated memory effects. In this study, we present a novel approach for modulating resistive and nonvolatile memory behavior in oxide semiconductors through the controlled injection and extraction of hydrogen. The proposed two-terminal device incorporates a hydrogen source layer that facilitates the diffusion of hydrogen ions into the active oxide matrix, where they form hydroxide (OH) bonds and locally modulate the electron concentration. This process induces a stable and reversible memory effect under an applied electric field. Hydrogen exchange predominantly occurs at the interface between the active and insulating layers, with the latter serving as a buffer to maintain an optimal hydrogen concentration. Furthermore, neural network simulations were performed by utilizing the synaptic characteristics controlled via hydrogen modulation, achieving a recognition accuracy of 97.2% on the MNIST data set. The effects of input data resolution and weight quantization on recognition performance were also systematically investigated and discussed. 2026-01-31T15:00:00Z