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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.
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.
Energy Product and Coercivity of a Rare-earth-free Multilayer FeCo/FePt Exchange Spring Magnet
김동유,Arqum Hashmi,홍지상 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.6
Using the full potential linearized augmented plane wave (FLAPW) method, we have explored the energy product and the coercivity field of rare-earth-free FeCo/FePt(001) multilayered exchange spring magnet systems. We have considered 5 and 7 monolayers (ML) of a FePt hard layer and 3, 5, 7, and 9 ML of a FeCo soft layer. The FeCo soft layers are found to show close to half metallic features, while the FePt hard layers manifest conventional metallic behavior. A giant perpendicular magnetocrystalline anisotropy energy (EMCA) is observed. For instance, an EMCA of 27.24 meV/cell is found in FeCo(9 ML)/FePt(7 ML) multilayer structure. The energy product almost linearly increases with increasing FeCo thickness, while the coercivity filed shows the opposite behavior. Interestingly, we have obtained that the multilayer structures display very large energy product and coercivity field. For example, FeCo(9 ML)/FePt(5 ML) multilayer has an energy product of about 82 MGOe and a coercivity field of about 130 KOe. Moreover, we find that the multilayer system may show enhanced coercivity field compared with that found in FeCo/FePt bilayer film structures, while the energy product is comparable to that observed in bilayer films. Therefore, our results may imply that the FeCo/FePt multilayer can be employed as a potential rare- earth-free permanent magnet material.
김동유,홍지상 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.5
Using the full potential linearized augmented plane wave (FLAPW) method, we have explored the magnetic properties of carbon doped wurtize ZnO. The unit cell has 48 atoms, and two carbon atoms are placed in the positions of oxygen or Zn sites. This corresponds to 8.3% doping concentration. We found that the Zn(C,O) has a magnetic state if the oxygen is substituted by a carbon atom,whereas there is no magnetic state when the Zn is replaced by carbon. Total energy calculations show that the (Zn,C)O has the most stable structure when the carbon dopants are placed closely. A magnetic moment of 0.22 µB in ground state is found, and this is in good agreement with experimental observation (Appl. Phys. Lett. 93 232507, 2008). The Zn(C,O) has been broposed to have a half-metallic state (Phys. Rev. Lett. 99 127201, 2007), but we have found no such a half metallic feature. In addition, the theoretically calculated carbon K-edge X-ray magnetic circular dichroism (XMCD) is presented, and the onset of XMCD spectra clearly depends on the carbon distribution.