Graphene-based Spintronic Devices Research Articles

The role of size in spin properties of zigzag graphene nanoribbon

The effects of ribbon size on the spin properties of zigzag graphene nanoribbon (ZGNR) with and without edge pentagon-heptagon reconstruction are investigated using spin-polarized density functional theory. It is found that when ribbon width is less than 26.31 A, the Coulomb and RKKY-like interaction between two ribbon-edges result in the edge state splitting. For a wider ZGNR, the interedge coupling is negligible. In addition to stabilizing the system and weakening the interedge coupling, the edge pentagon-heptagon reconstruction could demagnetize the ZGNR. In perfect and single-edge reconstructed ZGNR, the magnetic moment depends on ribbon width, and the change of magnetic moment becomes inconspicuous with increasing ribbon width. Double-edge reconstructed ZGNR shows nonmagnetic. It may be useful for fabricating graphene-based nanoelectronic and spintronic devices.

Spin-inversion in nanoscale graphene sheets with a Rashba spin-orbit barrier

Spin-inversion properties of an electron in nanoscale graphene sheets with a Rashba spin-orbit barrier is studied using transfer matrix method. It is found that for proper values of Rashba spin-orbit strength, perfect spin-inversion can occur in a wide range of electron incident angle near the normal incident. In this case, the graphene sheet with Rashba spin-orbit barrier can be considered as an electron spin-inverter. The efficiency of spin-inverter can increase up to a very high value by increasing the length of Rashba spin-orbit barrier. The effect of intrinsic spin-orbit interaction on electron spin inversion is then studied. It is shown that the efficiency of spin-inverter decreases slightly in the presence of intrinsic spin-orbit interaction. The present study can be used to design graphene-based spintronic devices.

FIRST-PRINCIPLES CALCULATION OF THE ELECTRONIC STRUCTURE AND MAGNETISM AT THE GRAPHENE/Ni(111) INTERFACE

A spin-polarized first-principles calculation of the atomic and electronic structure of the graphene/ Ni (111) interface is studied. The electronic structure of the graphene layer is strongly modified by interaction with the substrate and a behavior where magnetic moments are localized at the edges of nanoscale holes of isolated graphene does not happen in the defect-graphene/ Ni (111) system. The magnetic moment of the surface nickel atoms is lowered in the presence of the graphene layer and nanoscale holes of graphene, which control the strength of the hybridization between electronic states of graphene and Ni substrate. Our findings show that an electron spin in the graphene/ Ni (111) interface can be manipulated in a controlled way and have important implications for graphene-based spintronic devices.

Epitaxially Integrating Ferromagnetic Fe1.3Ge Nanowire Arrays on Few-Layer Graphene

We report vertical growth of ferromagnetic and metallic Fe1.3Ge nanowire (NW) arrays on few-layer graphene in a large area, induced by a relatively good epitaxial lattice match. Integrating well-aligned NW arrays onto graphene would offer a good opportunity to combine superb material properties of graphene with versatile properties of NWs into novel applications. Fe1.3Ge NWs are also synthesized on highly ordered pyrolytic graphite (HOPG). Fe1.3Ge NWs on graphene and HOPG show quite efficient field emission, which are ascribed to the well-interfaced vertical growth, a pointed tip, and high field-enhancement factor (β) of the NWs. The development of ferromagnetic metal NW−graphene hybrid structures would provide an important possibility to develop graphene-based spintronic, electronic, and optoelectronic devices.

ChemInform Abstract: Emergence of Magnetism in Graphene Materials and Nanostructures

AbstractReview: 131 refs.

Ultrathin epitaxial cobalt films on graphene for spintronic investigations and applications

Graphene is an attractive candidate in spintronics for a number of reasons, among which are its electric-field-controlled conductivity, its expected long spin lifetime and its two-dimensional nature. A number of recent proposals call for the development of high-quality ferromagnetic thin films in contact with graphene, whereas only thick polycrystalline or three-dimensional (nanoclusters) morphologies have been demonstrated so far. We report on the growth of flat, epitaxial ultrathin Co films on graphene using pulsed laser deposition. These display perpendicular magnetic anisotropy (PMA) in the thickness range 0.5–1 nm, in agreement with our first-principles calculations. PMA, epitaxy and ultra-small thickness bring new perspectives on graphene-based spintronic devices making use of the zero-field control of an arbitrary magnetization direction, band matching between electrodes and graphene, and interface phenomena such as the Rashba effect and electric field control of magnetism.

Theory of large tunneling magnetoresistance in a gapped graphene-based ferromagnetic superconductor F/(FS) junction

Abstract Coexistence of superconductivity and ferromagnetism in a gapped graphene-based system (FS) is theoretically investigated. The center-of-mass momentum, P, of a Cooper pair in FS is found to be P ∼ 2 E ex / ℏ v F 1 - ( m / E FS ) 2 , where m, Eex, EFS are the rest mass energy of the Dirac electron, exchange energy and the Fermi energy in the superconductor FS, respectively. It is unlike the nature in a conventional FFLO state where P ∼ 2 E ex / ℏ v F . This work studies the magneto effect on the transport property of a F/(FS) junction where F is a ferromagnetic gapless graphene. In this work, FS is achieved by depositing a conventional ferromagnetic s-wave superconductor on the top of gapped graphene sheet. The Zeeman splitting in FS induces spin-dependent Andreev resonance. The conductances effected by both spin-dependent specular Andreev reflections and spin-dependent Andreev resonances are investigated. The interplay between the spin-dependent specular Andreev reflection in the F region and the spin-dependent Andreev resonance in the FS region causes a very large tunneling magnetoresistance |TMR| ∼ 3000% for m → EFS, possibly valuable in the graphene-based spintronic devices. This is because of the coexistence of the superconductivity and ferromagnetism in FS and the relativistic nature of electrons in graphene.

Spin-polarized transport through a domain wall in magnetized graphene

Atomically thin two-dimensional layer of honeycomb crystalline carbon known as graphene is a promising system for electronics. It has a point-like Fermi surface, which is very sensitive to external potentials. In particular, Zeeman magnetic field parallel to the graphene layer splits electron bands and creates fully spin-polarized and geometrically congruent circular Fermi surfaces of particle and hole type. In the presence of electric field, particles and holes with opposite spins drift in opposite direction. These phenomena are likely to be of interest for developing graphene-based spintronic devices. A domain wall (DW) separating regions with opposite spin polarizations is a basic element of such a device. Here we consider a ballistic passage of spin-polarized charge carriers through DW in graphene. We also discuss the analogy between the generation of spin currents in graphene and in relativistic quark-gluon plasma, where the spin-polarized current is responsible for the phenomenon of charge separation studied recently at RHIC.

Rashba Effect in the Graphene/Ni(111) System

We report on angle-resolved photoemission studies of the electronic pi states of high-quality epitaxial graphene layers on a Ni(111) surface. In this system the electron binding energy of the pi states shows a strong dependence on the magnetization reversal of the Ni film. The observed extraordinarily large energy shift up to 225 meV of the graphene-derived pi band peak position for opposite magnetization directions is attributed to a manifestation of the Rashba interaction between spin-polarized electrons in the pi band and the large effective electric field at the graphene/Ni interface. Our findings show that an electron spin in the graphene layer can be manipulated in a controlled way and have important implications for graphene-based spintronic devices.