https://scholar.dgist.ac.kr/handle/20.500.11750/37 2026-04-04T13:36:35Z 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. 2026-01-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59017 Title: Exchange bias effect determined by anisotropic magnetoresistance in CoxNi1−xO/Ni0.8Fe0.2 bilayer system Author(s): Yoo, W.; Choo, S.; Lee, K.; Jo, S.; You, C.; Hong, Jung-Il; Jung, M. Abstract: Exchange bias effect is the unidirectional anisotropy induced by the interface between ferromagnetic (FM) and antiferromagnetic (AFM) layers below the Neél temperature of antiferromagnetic materials, leading to a shift of hysteresis loop. The effect of exchange bias has been studied for many years because of its possible application in spintronics, especially in spin valves for magnetic recording and sensor devices [1]. The essentials of exchange bias effect are not fully understood yet. It is generally accepted that the uncompensated moments in the AFM layer play an important role in pinning the spins at the interface and determine the strength of exchange bias field [2]. We prepared bilayer systems composed of the FM layer Ni0.8Fe0.2 and the AFM layer CoxNi1-xO (x = 0.3, 0.4, 0.5, and 0.6) by using the DC/RF magnetron sputtering method. Exchange bias field HEB, the shift field in hysteresis loop, was observed in all the Ni0.8Fe0.2/Co Ni1-xO bilayer systems. The changes of HEB were explicitly studied for various parameters such as the composition of AFM material x, the measured temperature T, and the angle θ of applied magnetic field. We measured anisotropic magnetoresistance (AMR) and analyzed the AMR data to extract the HEB, since the peak structure in AMR is not exactly same to the coercive field HC, unlike the magnetization data. We propose a new approach to analysis for AMR in determining HEB and HC along the field angle θ with respect to the field-cooling direction. The results were compared with the variations of HEB and HC simulated by Mauri model and spin-glass model [3]. 2015-05-11T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58991 Title: 자기 구조 제어 자성 소재 및 이의 응용 소자 제조 방법 Author(s): 홍정일; 윤성수; 최원창 Abstract: 본 개시는 중금속 층에 외부 전류를 인가함에 따라 강자성층의 스핀 정렬구조를 평행한 배열에서 비선형 정렬 구조로 인위적으로 제어할 수 있는 자성 소재를 제공한다. 본 개시의 일 실시예에 따른 자성 소재는 기판; 상기 기판 상에 형성된 제2 반강자성층; 상기 제2 반강자성층 상에 형성된 강자성층; 상기 강자성층 상에 형성된 제1 반강자성층; 및 상기 제1 반강자성층 사에 형성된 중금속층; 을 포함하고, 상기 중금속층에 인가하는 외부 전류를 제어하여 상기 강자성층의 자기 배열을 제어하는 것인, 자성 소재 및 이의 제조방법에 관한 것이다. https://scholar.dgist.ac.kr/handle/20.500.11750/58983 Title: Directly observed dynamics of distorted vortex cores including asymmetric Bloch walls utilizing soft X-ray microscopy Author(s): Im, M.; Han, H.; Jung, Min Seung; Fischer, P.; Hong, Jung-Il; Lee, K. 2018-04-23T15:00:00Z