https://scholar.dgist.ac.kr/handle/20.500.11750/10137 2026-11-05T04:49:23Z https://scholar.dgist.ac.kr/handle/20.500.11750/61076 Title: Development of thick Nd-Fe-B magnets with high coercivity and resistivity via a sandwich-structured grain boundary diffusion strategy Author(s): Kim, Hyuck-Joong; Kim, Tae-Hoon; Yoo, Jae-Gyeong; Lee, Dong Hyun; Kim, Jeongmin; Bae, Kyoung-Hoon; Lee, Sang-Hyub; Kim, Dong-Hwan; Lee, Junmin; Kim, Sumin; Lee, Jung-Goo Abstract: Sandwich-structured grain boundary diffusion (GBD) strategy using a low-melting-point Pr-Cu-Al-Ga (PCAG) alloy is proposed to overcome the diffusion-depth limitation of conventional grain boundary diffusion in Nd-Fe-B magnets. Applying the PCAG-GBD to both the outer surface and internal bonding interface enables the fabrication of thick Nd-Fe-B magnets with high coercivity comparable to that of thin single magnets treated via grain boundary diffusion. Microstructural analysis reveals the formation of Pr-rich shells and continuous grainboundary phases within whole stacked magnets, which effectively improve the coercivity of thick magnets by the GBD process. The diffusion-bonded interface exhibits markedly increased resistivity, reduced eddy-current heating, and improved mechanical strength. Overall, this approach offers a practical and scalable route for producing thick, high-performance Nd-Fe-B magnets suitable for next-generation electric drives and highfrequency applications. 2026-06-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/61041 Title: 열전소자의 저압 소결 접합 방법 및 이를 통해 제조된 열전소자 Author(s): 김정민; 김동환; 정석환; 김종태 https://scholar.dgist.ac.kr/handle/20.500.11750/60998 Title: Ferroelectric polarization and bandgap engineering in perovskite oxide via sulfur diffusion Author(s): Ahmad, Munir; Duong, Nguyen Xuan; Yun, Won Seok; Ullah, Asif; Kim, Hwan Min; Ullah, Aman; Khan, Raj Wali; Suleman, Muhammad; Kim, Ill Won; Yun, Seok Joon; Shin, Young-Han; Sheeraz, Muhammad; Bae, Jong-Seong; Ahn, Chang Won Abstract: Surface and interface conditions strongly influence the ferroelectric properties of oxide films because such regions significantly affect the output performance by controlling the internal physics of ferroelectric capacitors. In this work, we recover the dead layer, probably formed due to oxygen vacancies, at the ferroelectric film surface using sulfur-diffusion-based surface modification. For this purpose, Pb(Zr,Ti)O3 (PZT) thin films are deposited via chemical solution deposition, with subsequent sulfur incorporation for surface chemical modification. Specifically, an as-deposited PZT film on Pt(111)/TiO2/SiO2/Si(100) is spin-coated with a thiourea (CH4N2S) solution, with sulfur atoms incorporated into the oxygen-deficient dead surface layer through thermal diffusion. This sulfur diffusion substantially enhances the ferroelectric polarization and dielectric characteristics of the films. Such enhancements are associated with an increase in the tetragonality of the PZT crystal structure, as confirmed by X-ray diffraction analysis. Furthermore, X-ray photoelectron spectroscopy depth profiling reveals efficient sulfur diffusion within the dead layer to depths around 150 nm. The chemical incorporation of sulfur atoms at oxygen vacancies is responsible for enhancing ferroelectric and dielectric properties and reducing the bandgap. This study provides an approach for surface defect engineering in oxide ferroelectrics, offering new insights into the restoration of dead layers and their role in enhancing ferroelectric-photovoltaic performance. 2026-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60997 Title: Reversal of interlayer exchange coupling through post-annealing process accompanying asymmetric crystallization in Ta/Co2Fe6B2/MgO/Co2Fe6B2/ MgO heterostructures Author(s): Kim, Tae-Hwan; Cho, Jaehun; Kim, Soojung; Hong, Jung-Il; Kim, June-Seo Abstract: The effect of the post-annealing process accompanying asymmetric crystallization on interlayer exchange coupling in the Ta/Co2Fe6B2/MgO/Co2Fe6B2/MgO heterostructure is systematically investigated using ferromagnetic resonance. To induce structural asymmetry, the bottom Co2Fe6B2 layer is in contact with a Ta buffer, which acts as a boron absorber, while the top Co2Fe6B2 layer is encapsulated between two MgO layers. Structural analysis and magnetization measurements confirm that the selective crystallization of the bottom Co2Fe6B2 layer is well established upon a thermal annealing process, while the top Co2Fe6B2 layer is remained as a disordered state. The ferromagnetic resonance spectra reveal distinct coupling regimes depending on the annealing state. In as-grown samples, an antiferromagnetic (AFM)-like coupling is observed for MgO thicknesses, tMgO above 2.0 nm. In particular, the post-annealing process can trigger a sign reversal of the interlayer exchange coupling to a ferromagnetic (FM)-like state in the thick spacer regime (tMgO >= 2.6 nm). 2026-08-31T15:00:00Z