Electronic, structural, and transport properties of Ni-doped graphene nanoribbons (original) (raw)
Related papers
Spin-transport selectivity upon Co adsorption on antiferromagnetic graphene nanoribbons
The Journal of Chemical Physics, 2010
We investigate from first principles the electronic and transport properties of zigzag graphene nanoribbons in the presence of Co adatoms. Comparing different adsorption sites across the width, we find that the Co-C coupling is rather sensitive to the local environment. While a net spin polarization appears in all cases, the spin filtering effect is significantly enhanced when the Co adatom is at the edge, where the adsorption energy is maximized and a partial suppression of edge-associated transport channels occurs. We also probe the magnetic interaction in the nonbonding regime, for Co-graphene nanoribbon ͑GNR͒ distances ranging from adsorption totypical configurations. Our results indicate that Co-GNR coupling is still appreciable in an intermediate range, whereas it becomes vanishingly small in the limit ofdistances.
Edge-functionalized and substitutionally doped graphene nanoribbons: Electronic and spin properties
Physical Review B, 2008
Graphene nanoribbons are the counterpart of carbon nanotubes in graphene-based nanoelectronics. We investigate the electronic properties of chemically modified ribbons by means of density functional theory. We observe that chemical modifications of zigzag ribbons can break the spin degeneracy. This promotes the onset of a semiconducting-metal transition, or of a half-semiconducting state, with the two spin channels having a different band gap, or of a spin-polarized half-semiconducting state, where the spins in the valence and conduction bands are oppositely polarized. Edge functionalization of armchair ribbons gives electronic states a few eV away from the Fermi level and does not significantly affect their band gap. N and B produce different effects, depending on the position of the substitutional site. In particular, edge substitutions at low density do not significantly alter the band gap, while bulk substitution promotes the onset of semiconducting-metal transitions. Pyridinelike defects induce a semiconducting-metal transition.
Spin Dependent Electronic Transport in Edge Oxidized Zigzag Graphene Nanoribbon
Materials Today: Proceedings, 2018
In this work, we calculated spin dependent electronic transport properties of edge oxidized zigzag graphene nanoribbon (ZGNR). Three types of O-ZGNR structures were considered. In one, the edge states of the graphene nanoribbon were fully oxidized while the partial oxidation of the edge states was considered in the others. Simulation results, using density functional theory (DFT), revealed that the first configuration had no significant spin polarization effect. To the contrary, the other configurations had effect of spin polarization on the transport properties in both parallel and anti-parallel configurations. Total energy for non-magnetic, ferromagnetic and antiferromagnetic state is calculated to predict the ground state of the corresponding configuration. Spin polarization is estimated to assess the application of the considered structures in spintronics.
Electronic and magnetic properties of graphane nanoribbons
Physical Review B, 2010
In this study, we investigate the electronic and magnetic properties of graphane nanoribbons. We find that zigzag and armchair graphane nanoribbons with H-passivated edges are nonmagnetic semiconductors. While bare armchair nanoribbons are also nonmagnetic, adjacent dangling bonds of bare zigzag nanoribbons have antiferromagnetic ordering at the same edge. Band gaps of the Hpassivated zigzag and armchair nanoribbons exponentially depend on their width. Detailed analysis of adsorption of C, O, Si, Ti, V, Fe, Ge and Pt atoms on the graphane ribbon surface reveal that functionalization of graphane nanoribbons is possible via these adatoms. It is found that C, O, V and Pt atoms have tendency to replace H atoms of graphane. We showed that significant spin polarizations in graphane can be achieved through creation of domains of H-vacancies and CH-divacancies.
Tuning charge and spin excitations in zigzag edge nanographene ribbons
Scientific Reports, 2012
Graphene and its quasi-one-dimensional counterpart, graphene nanoribbons, present an ideal platform for tweaking their unique electronic, magnetic and mechanical properties by various means for potential next-generation device applications. However, such tweaking requires knowledge of the electron-electron interactions that play a crucial role in these confined geometries. Here, we have investigated the magnetic and conducting properties of zigzag edge graphene nanoribbons (ZGNRs) using the many-body configuration interaction (CI) method on the basis of the Hubbard Hamiltonian. For the half-filled case, the many-body ground state shows a ferromagnetic spin-spin correlation along the zigzag edge, which supports the picture obtained from one-electron theory. However, hole doping reduces the spin and charge excitation gap, making the ground state conducting and magnetic. We also provide a two-state model that explains the low-lying charge and spin excitation spectrum of ZGNRs. An experimental setup to confirm the hole-mediated conducting and magnetic states is discussed. C arbon nanomaterials have gained sustained interest in recent times due to their fascinating electronic properties, which arise from electronic confinement in a reduced-length scale. The successful isolation of graphene by mechanical exfoliation 1-3 has provided further impetus and has allowed for the first time the understanding of various properties in a truly two-dimensional context 4-6. The ultrahigh charge carrier mobility, transparency and mechanically flexible properties of graphene provide an excellent platform for futuristic device applications 7. Another intriguing aspect of graphene is the strong nanoscale and edge effects on its electronic and magnetic properties. The quasi-one-dimensional ZGNRs have drawn particular attention because of their peculiar edge ferrimagnetism that arises from the edge-localised states near the zigzag edges 8-10. Intensive studies ranging from mean-field to density functional theory have been performed to understand the carbon-based magnetism in ZGNRs 11-14. A recent experiment using scanning tunnelling spectroscopy (STS) reports the splitting of the density of states due to the edge magnetism for chiral graphene nanoribbons 15. These theoretical and experimental studies have motivated the fabrication of spintronics devices based on graphene nanoribbons. Although its edge-state magnetism seems to contradict the Mermin-Wagner theorem, which rules out the possibility of long-range ordering in quasi-one-dimensional systems 16 , a recent theoretical report using quantum Monte Carlo supports the existence of such a long spin-spin correlation length along the zigzag edge and justifies the picture obtained from the one-electron theories 17. Moreover, many previous studies suggest various ways to tweak the electronic properties of ZGNRs to achieve magneto-transport by means of doping, chemical modifications or external perturbations 18-22. From the viewpoint of device applications, it is necessary to clarify the interplay between the edge magnetism and the hole-doping effect, as the electron density in the graphene system can be easily tuned using the back gate electrode 23-25. However, the hole-doping effect on edge magnetism has not been studied with the appropriate inclusion of electron-electron interactions. In this study, we theoretically investigate the magnetic and conducting properties of ZGNRs and their response to doping. The development of gapless charge and spin excitations with hole doping, i.e., holemediated metallic ferromagnetism, is also discussed for the first time in terms of its potential applications. Our theoretical analysis is based on a large-scale numerical simulation using the many-body configuration interaction (CI) method with the complete active space (CAS-CI) approximation, which correctly includes quantum fluctuations. We show that the microscopic origin of magnetism in ZGNRs can be well understood on the basis of a generic two-state model.
Switching on magnetism in Ni-doped graphene: Density functional calculations
Physical Review B, 2008
Magnetic properties of graphenic carbon nanostructures, relevant for future spintronic applications, depend crucially on doping and on the presence of defects. In this paper we study the magnetism of the recently detected substitutional Ni (Ni sub ) impurities. Ni sub defects are non-magnetic in flat graphene and develop a non-zero magnetic moment only in metallic nanotubes. This surprising behavior stems from the peculiar curvature dependence of the electronic structure of Ni sub . A similar magnetic/non-magnetic transition of Ni sub can be expected by applying anisotropic strain to a flat graphene layer.
Magnetization profile for impurities in graphene nanoribbons
Physical Review B, 2011
The magnetic properties of graphene-related materials and in particular the spin-polarised edge states predicted for pristine graphene nanoribbons (GNRs) with certain edge geometries have received much attention recently due to a range of possible technological applications. However, the magnetic properties of pristine GNRs are not predicted to be particularly robust in the presence of edge disorder. In this work, we examine the magnetic properties of GNRs doped with transitionmetal atoms using a combination of mean-field Hubbard and Density Functional Theory techniques. The effect of impurity location on the magnetic moment of such dopants in GNRs is investigated for the two principal GNR edge geometries -armchair and zigzag. Moment profiles are calculated across the width of the ribbon for both substitutional and adsorbed impurities and regular features are observed for zigzag-edged GNRs in particular. Unlike the case of edge-state induced magnetisation, the moments of magnetic impurities embedded in GNRs are found to be particularly stable in the presence of edge disorder. Our results suggest that the magnetic properties of transitionmetal doped GNRs are far more robust than those with moments arising intrinsically due to edge geometry.
Physica E: Low-dimensional Systems and Nanostructures, 2018
We study the charge and spin transport in two and four terminal graphene nanoribbons (GNR) decorated with random distribution of magnetic adatoms. The inclusion of the magnetic adatoms generates only the z-component of the spin polarized conductance via an exchange bias in the absence of Rashba spin-orbit interaction (SOI), while in presence of Rashba SOI, one is able to create all the three (x, y and z) components. This has important consequences for possible spintronic applications. The charge conductance shows interesting behaviour near the zero of the Fermi energy. Where in presence of magnetic adatoms the familiar plateau at 2e 2 /h vanishes, thereby transforming a quantum spin Hall insulating phase to an ordinary insulator. The local charge current and the local spin current provide an intuitive idea on the conductance features of the system. We found that, the local charge current is independent of Rashba SOI, while the three components of the local spin currents are sensitive to Rashba SOI. Moreover the fluctuations of the spin polarized conductance are found to be useful quantities as they show specific trends, that is, they enhance with increasing adatom densities. A two terminal GNR device seems to be better suited for possible spintronic applications.