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RISS 인기검색어
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- 저자 : 하승석(Seung-Seok Ha) (검색결과 3 건)
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하승석(Seung-Seok Ha),유천열(Chun-Yeol You) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.2
We theoretically demonstrate that the interlayer exchange coupling (IEC) energy can be manipulated by means of an external bias voltage in a F₁/NM/F₂/S (F₁: ferromagnetic, NM: nonmagnetic metallic, F₂: ferromagnetic, S: semiconductor layers) four-layer system. It is well known that the IEC energy between two ferromagnetic layers separated by nanometer thick nonmagnetic layer depends on the spin-dependence of reflectivity to the F₁/NM/F₂/S four-layer system, where the reflectivities at the interface in NM/F₂ interface also depends on F₂/S interface due to the multiple reflection of an electron-like optics. Finally, the IEC energy depends on the spindependent electron reflectivity not only at the interfaces of F₁/NM/F₂, but also at the interface of F₂/S. Naturally the Schottky barrier is formed at the interface between metallic ferromagnetic layer and semiconductor, the Schottky barrier height and thickness can be tailored by an external bias voltage, which causes the change of the spin-dependent reflectivity at F₂/S interface. We show that the IEC energy between two ferromagnetic layers can be controlled by an external bias voltage due ti the electron-optics nature using a simple free-electron-like one-dimensional model.
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Brillouin Light Scattering을 이용한 GaAs/Fe/Au 구조의 자기이방성
하승석(Seung-Seok Ha),유천열(Chun-Yeol You),이석목(Sukmock Lee),Kenta Ohta,Takayuk Nozaki,Yoshishige Suzuki,W. Van Roy 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.4
It has been well-known that the Fe/GaAs heterostructure has a small lattice mismatch of 1.4 % between Fe and GaAs, and the Fe layer is grown epitaxially on the the GaAs substrate. There are rich physics are observed in the GaAs/Fe interface, and the spininjection is actively studied due to its potential applications for spintronics devices. We fabricated Fe wedge layer in the thickness range 0~3.4 ㎚ on the GaAs (100) surface with 5-㎚ thick Au capping layer. The magnetic anisotropy of the Fe/GaAs system was investigated by employing Brillouin light scattering (BLS) measurements in this study. The spin wave excitation of Fe layer was studied as the function of intensity and the in-plane angle of external magnetic field, and thickness of Fe layer. Also these various dependences were analyzed with analytic expression of spin wave surface mode in order to determine the magnetic anisotropies. It has been found that the GaAs/Fe/Au system has additional uniaxial magnetic anisotropy, while the bulk Fe has biaxial anisotropy. The uniaxial anisotropy shows increasing dependency respected to decreasing thickness of Fe layer while biaxial anisotropy is reduced with Fe film thickness. This result allows the analysis that the uniaxial anisotropy is originated from interface between GaAs surface and Fe layer.
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Vector Network Analyzer를 이용한 Py 박막의 강자성공명연구
신용확(Yong-Hwack Shin),하승석(Seung-Seok Ha),김덕호(Duck-Ho Kim),유천열(Chun-Yeol You) 한국자기학회 2010 韓國磁氣學會誌 Vol.20 No.1
Ferromagnetic resonance (FMR) measurement is an important experimental technique for the study of magnetic dynamics. We designed and set up the vector network analyzer ferromagnetic resonance (VNA-FMR) measurement system with home made coplanar waveguides (CPW). We examined 10-, 20-, 40-㎚ thick Py thin films to test the performance of the VNA-FMR measurement system. We measured S-parameter (transmission/reflection coefficient) of Py thin films on a CPW. Resonance frequency is investigated from 2.5 to 7 ㎓ for a field range from 0 to 490 Oe. The VNA-FMR data shows the resonance frequency increment when the external magnetic field increases. We also investigated Gilbert damping constant of Py thin film using resonance frequency (w<SUB>r</SUB>) and linewidth (Δ<SUB>w</SUB>). After investigating dependence of thickness, we find that an decrease in S-parameter intensity as Py thin film thickness decreases. And the FMR results show that the effective saturation magnetization, M<SUB>eff</SUB>, increase from 7.205(± 0.013) kOe to 7.840(± 0.014) kOe, while the film thickness varies from 10 to 40 ㎚.
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