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We have investigated the origin of thickness dependent spin reorientation transition (SRT) of B2 type FeCo alloy using the full potential linearized augmented plane wave method. It has been reported that FeCo alloy films on various substrates show a SRT from perpendicular to in-plane magnetization at an approximate thickness of 15 monolayers (MLs). The enhanced perpendicular magnetic anisotropy in bulk FeCo is attributed to a tetragonal distortion. However, we have found that the tetragonal distortion tends to suppress the magnetocrystalline anisotropy (MCA) energy at increasing film thickness in two-dimensional structure. In contrast, the magnitude of the shape anisotropy energy increases at increasing FeCo film thickness. Interestingly, the shape anisotropy overcomes the MCA and the SRT, from perpendicular anisotropy to in-plane magnetization, which occurs at a thickness of 15 ML. Consequently, we are able to clearly understand the physical mechanism of the thickness dependent SRT in terms of the competing reactions of these two counteracting contributions. [ABSTRACT FROM AUTHOR]

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 anisotropy system can be materialized in the Mn/Ag/Fe(001) structure. In addition, we also present the calculated x ray absorption spectroscopy and x ray magnetic circular dichroism of Fe and Mn layers. [ABSTRACT FROM AUTHOR]

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 calculated x-ray absorption spectroscopy and x-ray magnetic circular dichroism are presented. [ABSTRACT FROM AUTHOR]