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미세자기 동역학을 이용한 강자성 나노선의 자기 잡음 연구
윤정범(Jungbum Yoon),유천열(Chun-Yeol You),조영훈(Younghun Jo),박승영(Seung-Young Park),정명화(Myung-Hwa Jung) 한국자기학회 2010 韓國磁氣學會誌 Vol.20 No.1
We investigate the spin dynamics of the magnetic domain wall using the magnetic noise in the magnetic nanowire structure by employing micromagnetic simulations. Magnetic noise due to the thermal fluctuations in ferromagnetic materials is related to magnetic susceptibility and resonance frequency, which are important physical quantities in the study of the spin dynamics. In this study, we present the magnetic noise of the single domain without magnetic domain wall, and with the magnetic domain wall between two magnetic domains in ferromagnetic nanowires. It is confirmed that the Kittel equation with simple ellipsoid model with demagnetizing factor well describe the resonance frequency due to magnetic noise of the single domain. Besides, we find that there is a distinguishable additional resonance frequency, when a magnetic domain wall exists. It is verified that the additional resonance frequency is originated from the magnetic domain wall, and it is lower than one of the single domain. It implies that the spins inside the domain wall have a different effective field.
교환 바이어스 인위적 준강자성 기준층을 포함한 자기 터널 접합의 강자성 공명
윤정범(Jungbum Yoon),유천열(Chun-Yeol You),정명화(Myung-Hwa Jung) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.4
Spin dynamics of magnetic tunnel junctions with free and fixed reference layers is investigated by ferromagnetic resonance micromagnetic simulations. First, in magnetic tunnel junctions with an exchange biased synthetic ferrimagnetic reference layer, a magnetization direction of each layer and the tunneling magnetoresistance are calculated for a DC magnetic field. To investigate the spin exciting modes in magnetic tunnel junctions, we simulate the ferromagnetic resonance frequency spectra with small RF magnetic fields. Exciting modes of the tunneling magnetoresistance calculated by an included angle between free and reference layers is interpreted from those of each layer. Spin exciting modes are different according to a signs of the DC magnetic field. In a negative magnetic field, FMR frequency spectra of free and reference layers are well elucidated by the modified Kittel’s equation. However, in a positive magnetic field, there is no simple analytic solution related to FMR frequency spectra due to the coupled modes. Since ferromagnetic layers in magnetic tunnel junctions are interactive each other, careful considerations of the reference and fixed layer as well as the free layer are required for understanding on the spin dynamics of magnetic tunnel junctions with an exchange biased synthetic ferrimagnetic reference layer.
TiO₂ 씨앗층을 이용한 다양한 기판에서의 Co/Pd 층의 수직 자기 이방성에 대한 연구
강물빛(Mool-Bit Kang),윤정범(Jungbum Yoon),이정섭(Jeong-Seop Lee),유천열(Chun-Yeol You) 한국자기학회 2013 韓國磁氣學會誌 Vol.23 No.1
We investigate the perpendicular magnetic anisotropy in TiO₂/Co/Pd on GaAs(100), MgO(100), MgO(111), Si(100), and glass substrates. We find that the roughness of TiO₂ depends on the O₂ partial pressure in the magnetron sputtering process. The perpendicular magnetic anisotropies are found in all substrates with TiO₂ seed layer, and the perpendicular magnetic anisotropy of Co/Pd system is insensitive on the type of the substrate when the thickness of TiO₂ seed layer is thicker than 5 nm. However, MgO(111)substrate promotes TiO₂ rutile (111) structure, and it causes largest perpendicular magnetic anisotropy in TiO₂/Co/Pd(111) structures.