Jeonghwa Yang

Ferromagnetism induced by Zn vacancy defect and lattice distortion in ZnO

Through the full potential linearized augmented plane wave method, we have explored the vacancy defect induced magnetism in wurtize ZnO. It has been found that the Zn vacancy defect brings a spin polarized state in the nearest neighbor oxygen atoms, whereas the oxygen vacancy defect has no influence on the magnetism. However, it is found that the lattice distortion is a crucial factor for the Zn vacancy induced ferromagnetism because the ferromagnetic ground state cannot be achieved if there is no lattice distortion due to Zn vacancy defect. The magnetic moment of oxygen atom in the nearest neighbor from the Zn vacancy site is ranged from 0.10 to 0.19 μB and the spin polarized oxygen atoms have metallic feature in both spin states. These results are quite different from those found in other calculation [Q. Wang et al., Phys. Rev. B 77, 205411 (2008)]. In addition, we have found that the ferromagnetic exchange interaction among oxygen atoms is mediated by Zn 3d state. Along with these, the theoretically ca...

Ultrathin half metallic N and antiferromagnetic semiconducting C layers on MgO(001)

Using the full potential linearized augmented plane wave (FLAPW) method, we have explored the magnetic properties of ultrathin C and N layers on a MgO(001) surface. It has been found that the free standing C layer has a ferromagnetic (FM) ordering with a magnetic moment of 0.82 μ(B), while the free standing N layer with the same coverage displays an antiferromagnetic (AFM) state with a magnetic moment of 1.68 μ(B). Through a structure optimization procedure, we have found that both C and N adatoms are adsorbed on the O-top position in the presence of a MgO(001) surface. The ultrathin 0.25 monolayer coverage of C/MgO(001) film becomes a magnetic semiconductor and shows the c(2 × 2) AFM ground state with a magnetic moment of 0.62 μ(B). Surprisingly, the ultrathin N/MgO(001) manifests a half metallic state with a magnetic moment of 0.47 μ(B). In addition, the induced spin polarization in the O atom is found and this hybridization significantly affects the density of states (DOS) behavior. This peculiar DOS feature results in the opposite magnetic ground states of C and N layers on a MgO(001) surface. Additionally, it is found that the N/MgO(001) has a perpendicular magnetocrystalline anisotropy energy of 63 µeV. We also present theoretically calculated x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) results.

Ag-induced large perpendicular magnetic anisotropy in Mn/Ag/Fe(001)

Using the full-potential, linearized, augmented plane wave method, we have investigated the magnetic properties of body-centered-cubic Mn(2 monolayers [ML])/Fe(001), Mn(2 ML)/ Ag(1 ML)/Fe(001), and Mn(2 ML)/Ag(2 ML)/Fe(001). We find that the Mn overlayers have a layered antiferromagnetic ground state. However, the Ag spacer layer induces an oscillatory magnetic behavior in Mn film, because the relative direction of magnetization in Mn film is changed with increasing Ag layer thickness. In addition, we have realized that the optimized structure is a crucial factor to determine magnetic ground state of an ultrathin Mn/Fe(001) system. It is achieved that both Mn/Fe and Mn/Ag/Fe(001) systems manifest perpendicular magnetocrystalline anisotropy (MCA). Interestingly, the Ag spacer layer greatly enhances perpendicular magnetic anisotropy energy. The MCA energy in Mn(2 ML)/Fe(001) is about 137 μeV/cell, and it becomes 920 μeV in Mn(2 ML)/Ag(2 ML)/Fe(001). Therefore, we report that the large perpendicular magnetic...

Manipulation of spin reorientation transition by Au capping in body-centered cubic Ni(001) film

The thickness dependent magnetic properties of artificially prepared ultrathin body-centered cubic Ni films have been explored using the all electron full potential linearized augmented plane wave (FLAPW) method. We have considered two types of BCC Ni(001) films: (i) pure BCC Ni(001) and (ii) Au capped BCC Ni(001) in the range from 1 monolayer (ML) to 4 ML of Au capping coverage. The average magnetic moment of pure BCC Ni(001) is about 0.63 μB and a typical surface enhancement is found with a magnetic moment of 0.78 μB. In the presence of an Au capping layer, the magnetic moment of interface Ni is strongly suppressed to approximately 0.5 μB and this causes a reduction of average magnetic moment. Nevertheless, the Au adlayer has no meaningful induced magnetic moment. The BCC pure Ni(001) films always have in-plane magnetization up to 11 ML, but very interestingly the Au/Ni(001) shows a thickness dependent spin reorientation transition (SRT) from in-plane to perpendicular to the film surface. However, the thickness dependent SRT shows very irregular behavior. In addition, the calculated x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) have been presented.