[en] Magnetism and magnetostriction of rare earth intermetallic compounds, GdCo₂, GdFe₂, NdCo₂, SmCo₂, and ErCo₂, have been studied by using the first principles full-potential linearized augmented plane-wave method with the generalized gradient approximation. The calculated magnetostriction coefficients agree well with experiment. The itinerant electrons of transition metal elements are found to play a significant role in magnetoelastic coupling. The strong anisotropy of magnetostriction in GdCo₂ is explained. Contributions due to spatial anisotropic charge distribution of the incomplete 4f shells are calculated and discussed. [copyright] 2001 American Institute of Physics

[en] Electron energy loss spectra (EELS) of cubic and hexagonal BN, AlN, GaN, and InN have been calculated by using the first principles full potential linearized augmented plane wave method. Accurate calculations of linear optical functions are performed in a photon energy range up to 60 eV. The electron excitation energies related to the bulk plasmons are obtained for both reflection and transmission geometries. The predicted EELS data are discussed in comparison with available experimental results

[en] We present calculated second-harmonic-generation (SHG) spectra of the Si(001) surface based on a first-principles description of eigenvalues and eigenvectors using ab initio pseudopotentials. We also present SHG spectra for Ge-covered Si(001). The theoretical results explain all essential features of recent experimental SHG spectra of the Si(001)-(2x1) surface with low coverages of hydrogen and/or germanium, which alter the E₁ resonance in contrasting ways. The strong adatom specificity of the spectra results from redistribution of the adatom-related electronic states on the surface

[en] We perform first principles calculations based on density functional theory with the generalized gradient approximation (GGA) on the electronic and magnetic properties of carbon dopant in graphitic boron nitride (graphitic-BN) by the supercell method. It is found that carbon substitution for either boron or nitrogen atoms in graphitic-BN favours spin polarization over non-spin-polarization by 0.1 eV. The calculated electronic band structures show a spin-polarized, dispersionless band near the Fermi energy. The spin polarization is found to originate from the carbon dopant and can be attributed to the carbon 2p electron. The lower energies and the resistivity to curvature effect of the spin polarization suggest a possibility of ferromagnetic ordering of the carbon dopants in many realistic BN-based nanostructures which possess a hexagonal network such as nanotubes. Energies required for carbon substitution turn out to be within experimental access. The random substitution and the low doping energy indicate that graphitic-BN-based nanostructures can be viewed as candidates for metal-free magnet applications

[en] Density functional theory calculations with local spin density approximation (LSDA) have been performed to study the properties of VAs/GaAs interface. It was found that the half-metallicity of Cr layers close to the interface remains unchanged for an abrupt interface. The valence band minimum (VBM) of the minority spin lies well below the Fermi level of the majority spin (1.0 eV). The Schottky barrier height (SBH) to GaAs (n-type) is calculated to be 1.09 eV, which is acceptable regarding the band gap of GaAs. The conservation of halfmetallicity at the interface indicates that such a heterostructure is a promising candidate for high efficiency spin current injection at high temperature

[en] Linear and nonlinear [second harmonic generation (SHG)] optical functions of cubic and hexagonal BN, AlN, GaN, and InN have been studied by using the first-principles full-potential linearized augmented plane-wave method. Equilibrium lattice constants are determined from the total-energy minimization method. The calculated spectra of the second-order optical susceptibility show pronounced structures related to the two-photon resonances. In materials with heavy metals there are remarkable contributions from the single-photon transitions. Line shapes of the linear and particularly the nonlinear optical spectra of GaN and InN crystals are very sensitive to the interactions between the conduction bands and metallic d states. Studies of the nonlinear optical susceptibilities in both wurtzite and cubic crystals show high sensitivity of the SHG spectra to the changes of atomic structure. (c) 2000 The American Physical Society

[en] Using the full potential linearized augmented plane wave (FLAPW) method, we report the theoretical results that the carrier induced switching of magnetic interaction between two magnetic layers in Co(111)/Graphene/Ni(111) (Co/Gr/Ni) is predicted. The Co/Gr/Ni shows an antiferromagnetic (AFM) ground state when there are no external carriers. The antiferromagnetic interaction is still observed for hole carriers. Very interestingly, however, the magnetic exchange interaction between Ni and Co layers can be manipulated in such a way as to change an AFM to a ferromagnetic (FM) state by injecting external electrons if the electron carrier concentration is larger than 0.1 x 10¹⁴ per cm². Overall, we propose that a potential spin switching by external carriers or electric field can be realized in Co/Gr/Ni. Besides, the calculated DOS feature indicates that the Co/Gr/Ni system may manifest quite different transport properties when a bias voltage is applied. For instance, the current parallel to the film surface can be completely spin polarized from minority spin electrons. In contrast, the current perpendicular to the film surface will be positively spin polarized from majority spin electrons.

[en] First-principles calculations based on density functional theory were performed to study the stable geometries, electronic structure and magnetic properties of the adsorption of a single Mn atom on a graphitic ZnO sheet and a (9, 0) single-wall ZnO nanotube. For the graphitic ZnO sheet, the Mn atom prefers to reside above the center of a hexagon (H site), with a relatively large binding energy of 1.24 eV. The H site is also the most stable site for adsorption of an Mn atom inside the ZnO nanotube, with a large binding energy of 1.47 eV. In both of these cases, the total magnetic moment is 5.0 μ_B per Mn atom, which is the same as that of a free Mn atom. When the Mn atom is adsorbed outside the tube, the most energetically favorable site is the atop oxygen site. The magnetic moment is 3.19 μ_B for this configuration. The smaller magnetic moment is mainly due to the strong p-d mixing of O and Mn orbitals. The different adsorption behaviors are related to the curvatures of the nanostructures.

[en] Substrate-induced spin-orbit splitting in graphene on Ni, Au and Ag(111) is examined on the basis of density-functional theory. The Rashba splitting of π bands along the ΓM direction of the graphene surface Brillouin zone in graphene on Ni(111) is found to be very small (a few millielectronvolts), consistent with the experimental report of Rader et al. Instead, very strong Rashba splitting (near 100 meV) can be obtained for graphene with a certain stretch distortion on a Au substrate. It can be ascribed to the effective match in energy between the C 2p and Au 5d bands, obtained from the analysis of densities of states. The net charge transfer between the graphene and the substrates just affects the spin-orbit effect indirectly. The small spin-orbit splitting induced by the Ag substrates indicates that heavy metals do not always produce large SO splitting. Our findings provide important insights that are useful for understanding the metal-induced Rashba effect in graphene.

[en] We address the room-temperature (RT) carbon ferromagnetism by considering the magnetic states of low-dimensional carbons linked by sp-hybridized carbon atoms. Based on the spin-polarized density functional theory calculations, we find that the sp* orbitals of carbon atoms can bring magnetic moments into different carbon allotropes which may eventually give rise to the long-range ferromagnetic ordering at room temperature through an indirect carrier-mediated coupling mechanism. The fact that this indirect coupling is Fermi-level-dependent predicts that the individual magnetism of diverse carbon materials is governed by their chemical environments. This mechanism may help to illuminate the RT magnetic properties of carbon-based materials and to explore the new magnetic applications of carbon materials.