日本物理学会誌及びJournal of the Physical Society of Japanの月刊について

The isolation of graphene has triggered an avalanche of studies into the spin-dependent physical properties of this material, as well as graphene-based spintronic devices Here we review the experimental and theoretical state-of-art concerning spin injection and transport, defect-induced magnetic moments, spin-orbit coupling and spin relaxation in graphene Future research in graphene spintronics will need to address the development of applications such as spin transistors and spin logic devices, as well as exotic physical properties including topological states and proximity-induced phenomena in graphene and other 2D materials

Graphene Spintronics

We review the electronic properties of bilayer graphene, beginning with a description of the tight-binding model of bilayer graphene and the derivation of the effective Hamiltonian describing massive chiral quasiparticles in two parabolic bands at low energies. We take into account five tight-binding parameters of the Slonczewski–Weiss–McClure model of bulk graphite plus intra- and interlayer asymmetry between atomic sites which induce band gaps in the low-energy spectrum. The Hartree model of screening and band-gap opening due to interlayer asymmetry in the presence of external gates is presented. The tight-binding model is used to describe optical and transport properties including the integer quantum Hall effect, and we also discuss orbital magnetism, phonons and the influence of strain on electronic properties. We conclude with an overview of electronic interaction effects.

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The electronic properties of bilayer graphene.

This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.

https://link.aps.org/accepted/10.1103/RevModPhys.89.025006

Interface-induced phenomena in magnetism

A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented. Being semiconductors for one spin projection and metals for another, these substances are promising magnetic materials for applications in spintronics (i.e., spin-dependent electronics). Classification of HMFs by the peculiarities of their electronic structure and chemical bonding is discussed. The effects of electron-magnon interaction in HMFs and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered. Special attention is paid to the appearance of nonquasiparticle states in the energy gap, which provide an instructive example of essentially many-body features in the electronic structure. State-of-the-art electronic calculations for correlated d-systems are discussed, and results for specific HMFs (Heusler alloys, zinc-blende structure compounds, CrO2, and Fe3O4) are reviewed.

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Half-metallic ferromagnets: From band structure to many-body effects

Using density functional calculations we have investigated the local spin moment formation and lattice deformation in graphene when an isolated vacancy is created. We predict two competing equilibrium structures: a ground-state planar configuration with a saturated local moment of 1.5 ${\ensuremath{\mu}}_{B}$ and a metastable nonplanar configuration with a vanishing magnetic moment, at a modest energy expense of 50 meV. Though nonplanarity relieves the lattice of vacancy-induced strain, the planar state is energetically favored due to maximally localized defect states $(v\ensuremath{\sigma}$, $v\ensuremath{\pi})$. In the planar configuration, charge transfer from itinerant (Dirac) states weakens the spin polarization of $v\ensuremath{\pi}$ yielding a fractional moment, which is aligned parallel to the unpaired $v\ensuremath{\sigma}$ electron through Hund's coupling. As a by-product, the Dirac states $(d\ensuremath{\pi})$ of the two sublattices undergo a minor spin polarization and couple antiferromagnetically. In the nonplanar configuration, the absence of orthogonal symmetry allows interaction between $v\ensuremath{\sigma}$ and local $d\ensuremath{\pi}$ states, to form a hybridized $v{\ensuremath{\sigma}}^{\ensuremath{'}}$ state. The nonorthogonality also destabilizes the Hund's coupling, and an antiparallel alignment between $v\ensuremath{\sigma}$ and $v\ensuremath{\pi}$ lowers the energy. The gradual spin reversal of $v\ensuremath{\pi}$ with increasing nonplanarity opens up the possibility of an intermediate structure with a balanced $v\ensuremath{\pi}$ spin population. If such a structure is realized under external perturbations, diluted vacancy concentration may lead to $v\ensuremath{\sigma}$-based spin-$\frac{1}{2}$ paramagnetism. Carrier doping, electron or hole, does not alter the structural stability. However, the doping proportionately changes the occupancy of $v\ensuremath{\pi}$ state and hence the net magnetic moment.

Intertwined Lattice Deformation and Magnetism in Monovacancy Graphene

We present two newly designed two-dimensional (2D) thermoelectric materials ScP and ScAs, which are stretchable up to 14% as well as dynamically and thermally stable up to 700 K. From a systematic study using density-functional calculations, ab initio molecular dynamics simulations and phonon studies, we find that these compounds are narrow band gap semiconductors and crystallize in a puckered structure, as is the case for many experimentally realized 2D materials like phosphorene and arsenene. The transport properties of these compounds are estimated using the semi-classical Boltzmann transport approach. The lattice thermal conductivity (kl) in the unstrained system is estimated to be 8.3 and 5 W m−1 K−1 for ScP and ScAs respectively which are less compared to those of pristine phosphorene (24–110 W m−1 K−1) and arsenene (6–30 W m−1 K−1). Furthermore, the kl of these compounds becomes ultra-low (∼0.45 W m−1 K−1), when they are subjected to optimum tensile strain conditions. Highly dispersed bands of ScP and ScAs, due to strong p–d hybridization, give rise to large electrical conductivity (∼108 S m−1) which is two orders higher than that of arsenene and phosphorene. The strain also brings nearly a two- and three-fold increase in the Seebeck coefficient with respect to the unstrained value in these compounds. Overall, the strain tunable large figure of merit (∼0.65–0.9) makes these compounds promising thermoelectric materials.

Stretchable and dynamically stable promising two-dimensional thermoelectric materials: ScP and ScAs

The unique structural characteristics make the 2D materials potential candidates for designing negative electrodes for rechargeable energy storage devices. Here, by employing density functional the...

Density Functional Theory Studies of Si2BN Nanosheets as Anode Materials for Magnesium-Ion Batteries

The electrocatalytic properties of Cu, Ni, and Cu0.75Ni0.25 alloy are investigated for CO and CO2 reduction to methane by density functional calculations. We show that, as the Ni content increases in Cu(1–x)Nix (211) surfaces (x = 0, 0.25, and 1), the binding energies (ΔEs) of the adsorbates involved in the reaction mechanism decrease. Linear scaling relations are known to exist between ΔEs of adsorbates binding via a C (O) atom over pure transition metal surfaces. However, we find that alloying Cu and Ni has the potential for breaking these relations for certain pairs of adsorbates. The decrease in the repulsive Coulombic interaction between the adsorbate and the charges induced on the Cu–Ni alloy surface explains the adsorption site preference. The ΔE shift with respect to pure Cu is larger for species binding through C than O. Various trends exhibited by the binding energies are understood by analyzing the chemical bonding through local density of states and charge density isosurfaces of the bare and a...

CO and CO2 Electrochemical Reduction to Methane on Cu, Ni, and Cu3Ni (211) Surfaces

The effect of uniaxial strain on electronic structure and magnetism in ${\text{LaMnO}}_{3}$ is studied from a model Hamiltonian that illustrates the competition between the Jahn-Teller, superexchange, and double-exchange interactions. We retain in our model the three main octahedral distortions (${Q}_{1}$, ${Q}_{2}$, and ${Q}_{3}$), which couple to the Mn $({e}_{g})$ electrons. Our results show the ground state to be a type A antiferromagnetic (AFM) insulating state for the unstrained case, consistent with experiments. With tensile strain (stretching along the $c$ axis), the ground state changes into a ferromagnetic and eventually into a type ${\text{G}}^{\ensuremath{'}}$ AFM structure, while with compressive strain, we find the type A switching into a type G structure. The orbital ordering, which displays the well-known checkerboard ${x}^{2}\ensuremath{-}1/{y}^{2}\ensuremath{-}1$ structure for the unstrained case, retains more or less the same character for compressive strain, while changing into the ${z}^{2}\ensuremath{-}1$ character for tensile strains. While ${Q}_{1}$ and ${Q}_{3}$ are fixed by the strain components ${\ensuremath{\epsilon}}_{xx}$ and ${\ensuremath{\epsilon}}_{zz}$ in our model, the magnitude of the in-plane distortion mode $({Q}_{2})$, which varies to minimize the total energy, slowly diminishes with tensile strain, completely disappearing as the FM state is entered. Within our model, the FM state is metallic, while the three AFM states are insulating.

Birabar Nanda

Papers

Intertwined Lattice Deformation and Magnetism in Monovacancy Graphene

Stretchable and dynamically stable promising two-dimensional thermoelectric materials: ScP and ScAs

Density Functional Theory Studies of Si2BN Nanosheets as Anode Materials for Magnesium-Ion Batteries

CO and CO2 Electrochemical Reduction to Methane on Cu, Ni, and Cu3Ni (211) Surfaces

Magnetic and orbital order in LaMnO 3 under uniaxial strain: A model study