https://scholar.dgist.ac.kr/handle/20.500.11750/40 Sat, 04 Apr 2026 13:34:33 GMT 2026-04-04T13:34:33Z 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]. Mon, 11 May 2015 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/59017 2015-05-11T15:00:00Z 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. Mon, 23 Apr 2018 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/58983 2018-04-23T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/57880 Title: Magnon Characteristics in Metallic Bilayers through Unidirectional Magnetoresistance Author(s): Nguyễn, Thanh Hương Thi; Lee, Nyun Jong; Shiota, Yoichi; Lee, Hyun-Woo; Hong, Jung-Il; Kim, Kab-Jin; Ono, Teruo; Kim, Sanghoon Abstract: Magnon, quasi-particles arising from collective mode of spin excitations in magnetic materials, play an important role in understanding many spin-related phenomena, such as ultrafast spin dynamics and current-induced magnetic auto-oscillation. In particular, the concept of magnon current has been proposed as a potential replacement for electronic systems, offering data technology solutions without Joule heating-induced power dissipation. Therefore, the identification of magnon characteristics is highly demanded for realizing future magnonic applications. In this study, we investigate magnon characteristics in metallic bilayers using unidirectional magnetoresistance (UMR), a magnon-related phenomenon observed in ferromagnet/heavy metal bilayer structures. Through experiments focused on crystallographic dependence and non-local UMR measurement configurations, our results demonstrate that magnon can be efficiently generated in a system with I-sing type exchange interaction and the high energy magnons are much more efficient for spin pumping and spin current generation. Our results shed light on the underlying mechanism of energy-dependent magnonic phenomena and suggest a route to enhance the efficiency of magnon generation in the magnonic devices. Wed, 29 May 2024 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/57880 2024-05-29T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/56797 Title: Spin wave dynamics in epitaxial antiferromagnetic α-Fe₂O₃ thin film prepared by pulsed laser deposition method Author(s): Kim, Soo-Jung; Ha, Jae-Hyun; Baek, Eunchong; Kim, Jun-Su; Hong, Jung-Il; You, Chun-Yeol Abstract: Spin wave dynamics in antiferromagnetic materials, which has large group velocity (over 20 km/s) and long diffusion length (up to 10 μm), is getting more attention in many fields. [1-2] Especially, the α-Fe2O3, which has high bulk Dzyaloshinskii-Moriya interaction (DMI), low Gilbert damping constant (~10-5) and relatively low resonance frequency (tens to hundreds of GHz frequency) than other antiferromagnetic materials (over THz frequency), is emerging as a promising material recently. [3-5] However, the relevant spin wave dynamics studies are mostly dealing with the bulk single crystal structure, which shows considerably different characteristics in epitaxial thin film structure.In this study, we investigate the unique characteristics of spin wave dynamics in the α-Fe2O3 thin film at room temperature. The sample is deposited by using pulsed laser deposition (PLD) system with 85 nm of epitaxial Fe2O3 on the c-plane Al2O3 substrate. We confirm the crystallinity by X-ray diffractometer (XRD) and check the magnetic properties using SQUID-VSM. To measure the special features of spin wave dynamics in the α-Fe2O3 thin film, we used ferromagnetic resonance (FMR) and micro-Brillouin light scattering (μBLS). We detect the unexpected low frequency mode (f-) and multiple peaks of BLS signal which could be the clue of the new properties. Our results can widen the insight of the spin wave dynamics in the thin film α-Fe2O3 and the usage in the antiferromagnetic spintronics applications. Tue, 21 Nov 2023 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/56797 2023-11-21T15:00:00Z