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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]

We have investigated the magnetization reversal induced by carrier doped graphene (Be, B, N, O, or Cl doping) in Ni/Graphene/Co. In undoped case, the magnetic layers have an antiferromagnetic (AFM) coupling and this is still preserved from Be to O doping. We find magnetization reversal from AFM to ferromagnetic interaction induced by Cl doped graphene. In addition, the Ni and the Co layers show the opposite spin asymmetry near the Fermi level and this implies that each layer will generate completely different in-plane spin current in the same direction if an external electric field is applied. [ABSTRACT FROM AUTHOR]

Twinning is a fundamental mechanism behind the simultaneous increase of strength and ductility in medium- and high-entropy alloys, but its operation is not yet well understood, which limits their exploitation. Since many high-entropy alloys showing outstanding mechanical properties are actually thermodynamically unstable at ambient and cryogenic conditions, the observed twinning challenges the existing phenomenological and theoretical plasticity models. Here, we adopt a transparent approach based on effective energy barriers in combination with first-principle calculations to shed light on the origin of twinning in high-entropy alloys. We demonstrate that twinning can be the primary deformation mode in metastable face-centered cubic alloys with a fraction that surpasses the previously established upper limit. The present advance in plasticity of metals opens opportunities for tailoring the mechanical response in engineering materials by optimizing metastable twinning in high-entropy alloys.

The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. It is often assumed that the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the interfacial energy for the coherent fcc(1 1 1)/hcp(0 0 0 1) interface and the 'pseudo-interfacial energy' that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo-interfacial energies for six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and three paramagnetic Fe-Cr-Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence for both interfacial energies. The calculated pseudo-interfacial energies for the Fe-Cr-Ni steels agree well with the available literature data. We discuss the effects of strain on the description of planar faults via thermodynamic and ab initio approaches.

We demonstrate that the interface structure has a significant influence on the magnetic state of MnGa/Co films consisting of L1(0)-MnGa on face-centered-cubic Co(001) surface. We reveal an antiferromagnetic to ferromagnetic magnetization reversal as a function of the lateral lattice constant. The magnetization reversal mainly originates from localized states and weak hybridization at interface due to charge redistribution between muffin-tin spheres and interstitial region. The magnetic anisotropy energy of Mn/Co interface system is enhanced with increasing in-plane lattice constant, which is ascribed to the interface interactions and the above magnetization reversal.