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First-Principles Investigations of the Magnetic properties of Co(001) and V/Co(001) Thin Films
홍지상 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4
Based on the full potential linearized augmented plane wave (FLAPW) ab initio calculations, we explore various magnetic properties of ultra thin face centered cubic (fcc) Co(001) film and V adsorbed systems on Co(001) surface. We have found that the surface Co magnetic moment is greatly enhanced compared to that of an atom in a deeper layer. In the studies of V/Co(001) structures, it has been obtained that the V atom has no sizable sign of magnetic state for larger than monolayer (ML) coverage, whereas a large induced magnetic moment in V atom appears in 0.5-ML V coverage and surface alloy systems. The V atom always has antiparallel coupling to Co atoms. To provide a more comprehensive understanding of the magnetic properties, we have analyzed azimuthal quantum number resolved (m-resolved) density of states (DOS) behaviors for all systems explored in our calculations.
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홍지상 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.4
Using the full potential linearized augmented plane wave (FLAPW) method, we explored the magnetic properties of 8.3 % Cu doped ZnO varying the relative position between two Cu atoms. We found that the Cu atom had a magnetic moment of 0.6 μB and that the Cu doped ZnO displays half metallic feature. It has been realized that the most stable magnetic ground state is achieved when the Cu dopants are placed in the same basal layer of the tetrahedron, not in the uniformlydistributedstructure. The X-ray magnetic circular dichroism (XMCD) study shows that the spin polarized Cu atom has well separated L edge with a single peak feature. Moreover, the magneto-optical kerr effect (MOKE) was explored. The calculate kerr rotation angle is dependent on the relative distance of Cu atoms and the magnitude of kerr angle was about 0.5˚ in the most stable structure. We have also found that the major contribution to the kerr angle stems from the interband part.
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Ni/그래핀/Ni 의 자기적 성질에 관한 제일원리 연구
홍지상 한국물리학회 2014 New Physics: Sae Mulli Vol.64 No.1
We have investigated the magnetic properties of a Ni/graphene/Ni trilayer structure by using the full-potential linearized augmented plane-wave method. The graphene layer has been found to show a buckling feature of 0.32 °A, which causes a non-magnetic state in the Ni layer. Interestingly, the ferromagnetic coupling is induced between the two Ni layer due to external electron carriers whereas no magnetic moment is induced in Ni due to external hole carriers. This result may indicate an ability to manipulate the magnetic interaction of two magnetic by changing the external carrier type. 총포텐셜 선형보충평면파 계산방법 (full potential linearized augmented plane wave) 을 이용하여 Ni/그래핀/Ni 의 자기적 성질에 관한 연구를 수행하였다. 계산결과 그래핀층에 있는 2개의 탄소원자들이 평평한 면을 이루지 못하고 0.32 \AA 높이차이가 나타나고 이러한 이유에 의해서 Ni 원자에서 자기모멘트가 사라진다는 결과를 얻었다. 하지만, 외부에서 추가적으로 전자가 들어오게 되는 경우 두 개의 Ni 층사이에서 강자성 상호작용이 나타난다는 사실을 알게 되었다. 하지만, 이와 달리 정공 (hole)이 주입되는 경우에는 Ni 의 자기적 상태에 아무런 영향을 주지 못하고 비자성 상태가 유지된다는 것을 발견하였다. 따라서 외부전하의 종류에 의해서 Ni 층간의 자기적 상태를 변화시킬 수 있는 가능성이 있다는 결과를 얻었으며, 이는 그래핀층에 다양한 종류의 불순물 도핑을 통하여 본 연구에서 제시하는 결과를 실험적으로 확인할 수 있으리라 예상한다.
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홍지상(Jisang Hong) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.5
Permanent magnet is one of the most important parts in modern industry and the rare earth elements play an essential role for operation of permanent magnet. As is well known, the rare earth elements are mostly produced in China and the world is now facing serious problems owing to supply and demand imbalances. Many attempts have been performed to replace these rare-earth based permanent magnets by rare-earth free magnets, but they have not been successful so far. Regarding this issue, we discuss about an exchange spring magnet as a potential rare earth free permanent magnet structure.
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Structural and Magnetic Properties of the c(2 x 2) MnCu Alloy on Cu(001)
김동유,홍지상 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.6
Various magnetic properties of one monolayer of a c( 2 x 2 ) MnCu/Cu(001) surface alloy are explored using a state-of-the-art full potential linearized augmented plane wave (FLAPW) method. The optimized structure calculations show that the surface alloy has a buckling feature; in other words, the vertical position of surface Mn is 0.25 A higher than that of neighboring Cu atom in the presence of magnetic state with a high magnetic moment of 3.90 μΒ, whereas the paramagnetic alloy has a rather flat surface geometry. The MnCu surface alloy on Cu(001) is known to have a ferromagnetic (FM) ground state, but we have obtained that the surface alloy has a stripe type antiferromagnetic (AFM) ground state. This finding may explain the recent experimental X-ray magnetic circular dichroism (XMCD) study for the MnCu surface alloy.
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Magnetic Properties of MgN and MgC Films on MgO(001) Surfaces
김동유,홍지상 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.3
Using the full potential linearized augmented plane wave (FLAPW) method, we have explored the magnetic properties of one monolayer (ML) of MgN and MgC films on MgO(001) surfaces. In addition,the influence of a MgO capping layer on the magnetic states of MgC and MgN films has been investigated. We observed that both MgC/MgO(001) and MgN/MgO(001) display ferromagnetic (FM) state. Interestingly, we find that both free standing MgN film and MgN/MgO(001) systems display half metallic feature. The calculated magnetic moments of C and N in MgC/MgO(001)and MgN/MgO(001) are 0.3 μB and 0.57 μB, respectively. The essential magnetic properties of both systems are unchanged even in the presence of a MgO capping layer. In particular, the half metallic feature in MgN/MgO(001) is still maintained in both the MgN/MgO(001) and the MgO(1 ML)/MgN/MgO(001) systems. The adsorption energy calculations indicate that the MgC layer is physisorbed on MgO(001), while the MgN layer is chemisorbed. Due to the rigid half metallic feature and the character of adsorption, the MgN/MgO(001) can be utilized for potential spintronics purposes.
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Magnetic Anisotropy and XMCD Sum Rule in Ultrathin Fe/Ni Films: ab Initio Studies
김동유,홍지상 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.1
Various magnetic properties of ultrathin Fe/Ni films on Cu(001) surfaces are investigated using the full potential linearized augmented plane wave method (FLAPW). We find that the Fe/Ni film on the Cu(001) surface always has a magnetization perpendicular to the film's surface for pseudomorphic growth. However, an oscillatory magnetic anisotropy is found in the presence of a strain effect. In addition, theoretically calculated X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) are presented. Moreover, the validity of XMCD sum rule is explored.
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