https://scholar.dgist.ac.kr/handle/20.500.11750/11796 2026-07-21T12:11:19Z 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. 2026-04-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60208 Title: From Synthesis to Superconductivity: Hands-On Learning of Quantum Materials through YBCO Doping Author(s): Park, Jaemun; Cho, Beopgil; Rhee, Taeseong; Park, Keeseong Abstract: In the advancement of quantum materials research, consistent follow-up content in science education becomes paramount. In this article, we report how the synthesis and characterization of the high-temperature superconductor, yttrium barium copper oxide (YBCO), can effectively address this concern. Our exploration encompasses the comparison between pristine YBCO samples and La-, Ce-, and Fe-doped variants to examine the emergence and suppression of superconductivity. Magnetic levitation experiments under liquid nitrogen conditions revealed the presence of the flux pinning effect in La- and Ce-doped samples, whereas it was absent in Fe-doped samples, consistent with temperature-dependent resistance measurements. X-ray diffraction analysis confirmed that La atoms successfully substituted for the Y site, while Ce atoms remain incompatible with the YBCO phase under our synthesis conditions. In contrast, when Fe atoms replace the Cu site, they suppress the superconductivity and transform the crystal structure from orthorhombic to tetragonal. We suggest that our study not only provides insights into the physical properties of YBCO through introducing various dopants but also serves as a benchmark for educators developing analogous or extended experiments. 2026-01-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59993 Title: Accurate Assessments of the Electronic Structures of Ultrathin PtSe2: Bandgap Quantification and Critical Thickness for the Metal-Semiconductor Transition Author(s): Kim, Hansung; Cha, Janghwan; Seo, Jong Hyeok; Cho, Beopgil; Park, Jaemun; Park, Keeseong; Watanabe, Kenji; Taniguchi, Takashi; Ha, Dong Han; Kwon, Jihwan; Seo, Sunae; Kim, Yong-Sung; Jung, Suyong Abstract: Ultrathin PtSe2, a member of the group-10 transition metal dichalcogenides, has emerged as a promising two-dimensional material due to its layer-dependent, tunable bandgap. Notably, a unique semiconductor-to-metal transition is predicted as the layer number of this material increases; however, pinpointing the exact critical thickness for this transition and reliably quantifying the energy gaps of the semiconducting layers remain formidable challenges. In this work, all-van der Waals assembled multiprobe schemes and planar tunnel junctions are employed to systematically investigate the thickness-sensitive charge transport properties and energy gaps of ultrathin PtSe2 films. Temperature-dependent measurements reveal that PtSe2 exhibits semiconducting behavior from monolayer to five layers, with a transition to a semimetallic state at six layers. Furthermore, using electron tunneling spectroscopy, we accurately quantify the energy gaps of monolayer, bilayer, and trilayer PtSe2 and identifies that PtSe2 in monolayer form behaves as an n-type semiconductor but intriguingly transitions to a p-type semiconductor in bilayer form. First-principles calculations highlight the importance of correctly evaluating interlayer distances to select the appropriate density functional theory functional, enabling reliable predictions of the critical thickness of ultrathin PtSe2 for the semiconductor-to-metal transition and corresponding electronic structures. 2025-07-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59039 Title: Evidence for orbital Fulde-Ferrell-Larkin-Ovchinnikov state in the bulk limit of 2H-NbSe2 Author(s): Cho, Chang-woo; Lortz, Timothee T.; Lo, Kwan To; Ng, Cheuk Yin; Chui, Shek Hei; Allan, Abdel Rahman; Abdel-Hafiez, Mahmoud; Park, Jaemun; Cho, Beopgil; Park, Keeseong; Yuan, Noah F. Q.; Lortz, Rolf Abstract: The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is an unusual superconducting phase that survives beyond the Pauli paramagnetic limit through spatial modulation of the order parameter. An even more exotic variant-the orbital FFLO state-was recently reported in thin flakes of 2H-NbSe2, involving the interplay of Ising spin-orbit coupling and orbital pair breaking. Here, we report thermodynamic signatures consistent with an orbital FFLO state in bulk 2H-NbSe2, based on high-resolution magnetization and torque measurements under strictly parallel to the NbSe2 basal plane. In the magnetic phase diagram, a crossover to a first-order transition appears above 3 T and disappears with slight field misalignment, indicating field-angle dependent Pauli-limited behavior. Additionally, we observe a reversible step-like anomaly within the superconducting state, and a pronounced six-fold in-plane modulation of the upper critical field above this phase transition. These results suggest that the orbital FFLO state is likely realized even in the bulk limit of 2H-NbSe2. 2025-07-31T15:00:00Z