Possible graphitic-boron-nitride-based metal-free molecular magnets from first principlesstudy

Ab initio electronic structure calculations, based on density-functional theory within the generalized gradient approximation, on LaSr2Mn2O7 are reported. The bulk electronic structure shows a gap in the minority-spin channel, while the Fermi energy lies at the bottom of the minority conduction band. At the surface of LaSr2Mn2O7, the magnetic moment per formula unit and the spin polarization at the Fermi energy are lowered with respect to the bulk values.

The geometric and spin-resolved electronic structure of a graphene-adsorbed Ni(111) surface has been investigated by density functional theory (DFT) calculations without and with a semiempirical long-range dispersion correction (DFT-D). DFT calculations with generalized gradient approximation (GGA) functional cannot predict well about the adsorption properties of graphene to the Ni(111) surface. While DFT-D calculations with the same GGA functional give reasonable values of the adsorption energy and layer distance from graphene to the substrate. The geometry of top_fcc is the most energetically favorable in all geometries. Strong hybridization of graphene with the ferromagnetic Ni substrate induces significant shift partially in graphene π states towards the Fermi level yielding spin polarization. The spin polarization is positive at the shallow levels of modified π states and slightly negative at the deeper levels of fundamental π states, which is indicated by the calculated spin density distributions and plane-averaged density of states at the vacuum side. The opposite spin polarization is consistent with our experimental result of spin asymmetry obtained by spin-polarized metastable-atom de-excitation spectroscopy measurements.

The structural, electronic, elastic, vibrational, and thermodynamic properties of HoX (X=Sb, Bi)

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We performed ab initio calculation on the pristine and carbon-doped (5,5) and (9,0) BN nanotubes. It was found that carbon substitution for either a single boron or a single nitrogen atom in the BN nanotubes can induce spontaneous magnetization. Calculations based on density functional theory with the local spin density approximation on the electronic band structure revealed a spin polarized, dispersionless band near the Fermi energy. The magnetization can be attributed to the carbon 2p electron. Compared to other theoretical models of light-element or metal-free magnetic materials, the carbon-doped BN nanotubes are more experimentally accessible and can be potentially useful.

The process of copper oxidation has been thoroughly studied for many years, yielding a significant understanding of its kinetics and chemistry. However, the possible roles of surface spin polarization in important issues such as oxidation rates have not been widely explored despite the triplet nature of molecular oxygen. Here, we investigate the spin-dependent oxidation of copper films by triplet O2, exploiting engineered ferromagnetic substrates to impose controlled surface spin polarization. Three sample architectures that enable comparison between spin-polarized and nonpolarized surfaces were implemented to enable direct comparison between regions of varying spin polarization on the same sample. Combining various surface-sensitive techniques, including atomic force microscopy, Kelvin probe force microscopy, ellipsometry, and magneto-optical Kerr effect, we followed oxide growth kinetics and electronic property changes over time scales from minutes to weeks. Our results demonstrate that spin-polarized surfaces exhibit a significant acceleration in copper oxide formation compared with less polarized regions. The difference appears to be driven by a preference toward the formation of cupric oxide (CuO), the second oxidation state of copper, over cuprous oxide (Cu2O), the first oxidation state. We suggest that the results are related to the different magnetic properties of each oxide. Our data also reveal that the CuO oxidation phase propagates from the Cu film edges toward the center of the sample. These findings provide direct evidence of the surface-spin influence on metal oxidation kinetics and support the notion that spin polarization can induce a lower activation energy barrier for electron transfer between metal to triplet O2. Beyond advancing the fundamental understanding of corrosion chemistry, this spin-dependent control of surface reactivity opens potential avenues for tailored catalyst design, spintronic device stability, and corrosion mitigation strategies.

Introducing a periodic array of holes, i.e., an antidot lattice, in a graphene sheet has been suggested as a route towards the tantalizing objective of ``opening the gap'' in this otherwise zero-gap semiconductor. Combining density-functional and mean-field Hubbard tight-binding methods, we study the effect of spin polarization on graphene antidot lattices (GALs). Focusing on GALs with extended zigzag edges, we systematically investigate the geometry dependence of spin polarization, electronic structure, and band gaps. A scaling law for the band gap is established, demonstrating marked deviations from that of circular holes without spin polarization. Furthermore, we estimate the robustness of the magnetic ordering against raised temperature and doping and, finally, consider how the optical properties are modified by spin polarization. Our results demonstrate that large, stable band gaps are expected for a range of geometries.

Specific features of electronic structure and linear optical properties of some pseudocubic compounds

Computational calculations based on density functional theory were carried out to investigate ferromagnetism in gallium arsenide (GaAs) heavily doped with Fe atoms that can substitutionally occupy gallium (Ga) or arsenic (As) sites in the zinc-blende-like crystal structure. The calculations were performed within the spin polarized density functional theory (DFT) and generalized gradient approximation (GGA) with full potential linearized augmented plane wave (FP-LAPW) method. We investigate and discuss the ab initio calculation results focusing on properties intrinsically important for spintronic applications, such as spin polarization and magnetic anisotropy. The density of states (DOS) was calculated with substitution of Fe atoms in the As and Ga sites, giving the electronic properties, as well as the magnetic ground state. According to DFT calculations, heavily doped GaAs with 25 at. % of Fe becomes a ferromagnetic metal with spin polarization as high as 69% at Fermi level. This is corroborated by experimental results previously published in literature.

Stoner excitations in the ferromagnetic 3d metals, although fundamental in the theory of itinerant magnetism, have never been observed directly, e.g., by inelastic neutron scattering because the energies involved are too high for present-day neutron sources. We show that these excitations are readily measure by spin-polarized electron energy loss spectroscopy (SPEELS). We have measured the spin polarization spectrum of electrons scattered from a Fe-based ferromagnetic metallic glass (Fe82B12Si6) using unpolarized primary electrons in the energy range Ep=20–240 eV. While the spin polarization P for elastically scattered electrons is always small (*P*≤3%) a maximum of P is found around 2.2 eV energy loss. The value of the maximum Pmax decreases with increasing primary energy (Pmax=12% for Ep=20 eV, Pmax=3% for Ep=240 eV). This maximum is caused by spin-flip (Stoner) excitations (via exchange). In this process an incoming spin-down electron falls into the empty part of the spin-down density of states above EF and excites a spin-up electron from the occupied part of the majority density of states. The energy loss of 2.2 eV then corresponds to the ferromagnetic exchange splitting. This interpretation is corroborated by recent model calculations by Glazer and Tosatti which show good agreement with the experimental data. The spin polarization as a function of energy loss and the dependence on proimary energy are well reproduced by the calculatioons. Kirschner et al. showed that the Stoner excitatioons can also be observed by a slightly different experimental approach, i.e., by using spin-polarized primary electrons and measuring the asymmetry of the scattered intensity upon reversal of the primary spin polarization. For a Ni(110) surface they found an asymmetry maximum around 300 meV energy loss. This value again corresponds to the ferromagnetic exchange splitting. The novel technique of spin-polarized electron energy loss spectroscopy, which is complementary to spin-polarized photoemission and inverse photoemission, promises to yield new insights into the electronic structure and the electronic excitation spectrum of itinerant ferromagnets and their temperature dependence, e.g., for ferromagnetic alloys.

Electronic structure of REFe2 (RE = Dy, Ho and Er) intermetallic compounds: Ab initio spin-density functional theory

A comprehensive investigation of structural and magnetic phase stability, electronic, magnetic and thermoelectric properties of Co2FeZ (Z = Al, Ga, Si, Ge, S, Se and Te) Full Heusler alloys

We present a formulation of the scattering matrix method for spin-dependent electron transport in a quantum waveguide with spin-orbit interaction (SOI). All the required Hamiltonian matrices needed in the implementation of the formulation are represented in a basis of the transverse spatial eigenstates and the spin eigenstates of the leads. Thus the method has great flexibility and can be easily applied to systems with complex geometrical structure, potential distribution, and SOI strength profile. Also, the method is numerically stable and can be used to treat spin-dependent multisubband scattering processes accurately. We have applied the method to the spin-dependent electron transport in quasi-one-dimensional (Q1D) conductors, with a region of the Rashba SOI of uniform strength and with a region containing a Rashba SOI superlattice, made from a semiconductor heterostructure. The total conductance, spin-dependent conductances, and spin polarization of the system are calculated for a fully spin-polarized electron beam injected from a lead into the SOI region. For the Q1D conductor with a single region of the Rashba SOI, it is found that when the Fermi energy is set at a value, for which the total conductance is at a plateau, the spin-dependent conductances show regular oscillations with increasing SOI strength. This is approximately true even when the total conductance is at a high plateau and thus multiple subbands in the waveguide are open for conduction. However, when the Fermi energy is set at a value close to the onset of a subband (with the subband index $n\ensuremath{\geqslant}2$), the spin-polarized conductances plotted against the SOI strength and the SOI region length show sharp resonance features or complex fluctuations. These irregular conductance characteristics arise from SOI-induced strong coupling between subbands. For the Q1D conductor modulated by an array of strong Rashba SOI stripes, the total conductance shows regular superlattice behavior, while the spin-dependent conductances show complex behavior with regions of slow oscillations and regions of rapid oscillations. As in the Q1D conductor with a single SOI region, the slow oscillations are found in the energy regions where the total conductance is at plateaus. However, the rapid oscillations appear at energies close to the onsets of subbands with the subband index $n\ensuremath{\geqslant}2$. These oscillations originate from strong spin scattering by localized states formed in the SOI-modulated superlattice region.

First-principles total energy calculations have been performed using full potential linear-augmented-plane-wave method within the framework of density functional theory to study the structural, electronic, magnetic and optical properties of the Pb 1-x Eu x Se and Pb 1-x Eu x Te (0 ≤ x ≤1) alloys in the ferromagnetic (FM) ordering. The calculations have been extended to treat the strongly localized f electrons of Eu atom by the self-interaction correction (SIC) approach. For structural optimization, the Wu and Cohen generalized gradient approximation (GGA) functional has been used, whereas for calculating electronic properties, the GGA parameterization scheme formulated by Engel and Vosko (EV) has also been utilized. It has been observed that the use of experimental value of Coulomb parameter (Uf- expt. ) within the SIC does not yield an accurate EuSe and EuTe energy band structure. The improvement in the electronic band structures of nonmagnetic PbSe / PbTe and ferromagnetic EuSe / EuTe have been achieved by considering the effects of spin–orbit coupling for Pb atoms, by a suitable choice of U and by treating the U values for Eu atom's f and d electrons as parameters. The electronic and optical properties of FM Pb 1-x Eu x Se in agreement with experiments can be achieved by combining EV GGA with a Hubbard U < Uf- expt. , however, a stronger and stable AFM coupling in EuTe leaves the above scheme unable to provide good electronic structure of FM Pb 1-x Eu x Te . In case of Pb 1-x Eu x Se the nonlinear behaviour of electronic structure is reflected in the optical properties of Eu -doped PbSe that have been studied in terms of incident photons' energy dependent complex dielectric function.

Electronic structure and magnetic properties of Europium monochalcogenides ($\mathrm{Eu}X$, $X=\mathrm{O}$, S, Se, and Te) have been investigated by the full potential linear muffin-tin orbital method. The generalized gradient approximation (GGA) including on site Coulomb interaction of $5d$ and $4f$ states $(\mathrm{GGA}+{U}_{d}+{U}_{f})$ has been used to describe the complicated properties of $\mathrm{Eu}X$. The $\mathrm{GGA}+{U}_{f}$ band structure underestimates the band gap. $\mathrm{GGA}+{U}_{d}+{U}_{f}$ gives better agreement in terms of band gap and the positions of $4f$ bands of $\mathrm{Eu}X$. $\mathrm{GGA}+{U}_{d}+{U}_{f}$ gives much improved Kerr spectra for all the $\mathrm{Eu}X$ over the standard LSDA and $\mathrm{GGA}+{U}_{f}$ spectra although the magnitude of the first peak is less satisfactory in the dielectric function spectra. The Coulomb correlation effects among $4f$ and $5d$ electrons of Eu play important role to determine the optical spectra of $\mathrm{Eu}X$.