Magnetic Properties Of Graphene Research Articles

Modification of the Magnetic and Electronic Properties of the Graphene‐Ni(111) Interface via Halogens Intercalation

AbstractElectronic decoupling of graphene from metallic and semiconducting substrates via intercalation of different species is one of the widely used approaches in studies of graphene. In the present work, the modification of the electronic and magnetic properties of graphene on ferromagnetic Ni(111) layer via intercalation of halogen atoms (X = F, Cl, Br) is studied using the state‐of‐the‐art density‐functional theory approach. It is found that in all gr/X/Ni(111) intercalation systems, a graphene layer is fully electronically decoupled from the ferromagnetic substrate; however, different kind (electron or hole) and level of doping can be achieved. Despite the extremely small magnetic moment of C‐atoms in graphene observed after halogens intercalation, the sizeable spin‐splitting up to 35 meV for the linearly dispersing graphene π bands is found. The obtained theoretical data bring new ideas on the formation of the graphene‐ferromagnet interfaces where spin polarized free‐standing graphene layer can be formed with the possible application of these systems in electronics and spintronics.

Core-shell CoFe2O4@C nanoparticles coupled with rGO for strong wideband microwave absorption

Strong absorption and large bandwidth are two contributors to materials’ absorbing performance. In this work, a series of multi-element core-shell magnetic nano-particle composite layered graphene absorbing materials CoFe2O4@C/rGO (CCr) were prepared by adjusting carbon shell thickness. The CCr at a low thickness achieved strong microwave absorption and a wide effective absorption bandwidth. Not only the core-shell structure of the magnetic nanoparticle CoFe2O4@C (CFO@C) increases the interface loss, but both the coating carbon shell and the core CoFe2O4 (CFO) are beneficial to improve impedance matching. Due to the synergistic effect of the dielectric and magnetic properties of graphene and ferrite, CCr possessed high absorption performance, and its minimum reflection loss reached (RLmin) −52.5 dB when the thickness was only 2 mm. At the same time, the effective absorption bandwidth (EAB) was 5.68 GHz when the thickness was only 1.7 mm. The chemically stable core-shell dielectric nanocomposite provided a new solution for preparing materials with excellent chemical structure and high absorbing properties.

Investigation of the Magnetic and Electronic Properties of Pyrrolic N-doped Graphene Using Density Functional Theory

Modifying the bandgap and magnetic properties of graphene is one of the keys to realizing graphene-based nanodevices. Here, we investigate the effect of nitrogen concentration in the pyrrolic bond configuration on the magnetic properties of graphene using the spin-polarized Density Functional Theory (DFT) method. For a better understanding, we also calculated the electronic and structural properties of the pyrrolic N-doped graphene. This study used three models, i.e., pristine graphene and pyrrolic N-doped graphene with two nitrogen concentrations (N x G1 − x , x=2.000% and 3.125%). We observed that the higher the dopant concentration, the more the deformation of the planar structure in pyrrolic N-doped graphene. This is indicated by the more wrinkled structure that forms. Semi-metal to metal transitions were also observed in both models of pyrrolic N-doped graphene. Asymmetry behavior in the spin-polarized density of states (SPDOS) was also observed in both pyrrolic N-doped graphene models. The total magnetic moment increases with increasing dopant concentration. At a concentration of 2.000%, the resulting total magnetic moment is 1.68 µB/cell, and at a concentration of 3.125%, it is 1.74 µB/cell. We suggest that defects and nitrogen impurities play a crucial role in the transition of the magnetic properties of graphene. Our result shows that nitrogen-doped graphene with pyrrolic configuration is a promising candidate for nanomagnetic devices.

First-principles calculations study of the configurations, structural, electronic and magnetic properties of graphene and h-BN monolayers and bilayers adsorbed on Co(0001) surface

We carried out first-principles calculations study of the configurations, structural, electronic and magnetic properties of a graphene (h-BN) monolayer and bilayer adsorbed on Co(0001) surface. Binding energies, distances of the carbon C, boron B, or nitrogen N atoms from the Co surface and optimized lattice parameter for all configurations are reported. Induced magnetic moments on C, B and N atoms are determined as well as the magnetic moments carried by the cobalt Co surface atoms in presence of graphene or h-BN. Our results are discussed by means of hybridization of graphene (h-BN) and cobalt orbitals and charge transfer at the graphene (h-BN)/Co interface based on band structure and density of states calculations. Comparison between monolayers and bilayers systems highlighted the preponderant role of the first layer in contact with cobalt for the bilayers cases.

Alkaline earth atom doping-induced changes in the electronic and magnetic properties of graphene: a density functional theory study.

Density functional theory was used to investigate the effects of doping alkaline earth metal atoms (beryllium, magnesium, calcium and strontium) on graphene. Electron transfer from the dopant atom to the graphene substrate was observed and was further probed by a combined electron localization function/non-covalent interaction (ELF/NCI) approach. This approach demonstrates that predominantly ionic bonding occurs between the alkaline earth dopants and the substrate, with beryllium doping having a variant characteristic as a consequence of electronegativity equalization attributed to its lower atomic number relative to carbon. The ionic bonding induces spin-polarized electronic structures and lower workfunctions for Mg-, Ca-, and Sr-doped graphene systems as compared to the pristine graphene. However, due to its variant bonding characteristic, Be-doped graphene exhibits non-spin-polarized p-type semiconductor behavior, which is consistent with previous works, and an increase in workfunction relative to pristine graphene. Dirac half-metal-like behavior was predicted for magnesium doped graphene while calcium doped and strontium doped graphene were predicted to have bipolar magnetic semiconductor behavior. These changes in the electronic and magnetic properties of alkaline earth doped graphene may be of importance for spintronic and other electronic device applications.

Tailoring Electronic and Magnetic Properties of Graphene by Phosphorus Doping.

The electronic and magnetic properties of graphene can be modulated by doping it with other elements, especially those with a different number of valence electrons. In this article, we first provide a three-dimensional reconstruction of the atomic structure of a phosphorus substitution in graphene using aberration-corrected scanning transmission electron microscopy. Turning then to theoretical calculations based on the density functional theory (DFT), we show that doping phosphorus in various bonding configurations can induce magnetism in graphene. Our simulations reveal that the electronic and magnetic properties of P-doped (Gr-P) and/or phosphono-functionalized graphene (Gr-PO3H2) can be controlled by both the phosphorus concentration and configurations, ultimately leading to ferromagnetic (FM) and/or antiferromagnetic (AFM) features with the transition temperature up to room temperature. We also calculate core-level binding energies of variously bonded P to facilitate X-ray photoelectron spectroscopy-based identification of its chemical form present in P-doped graphene-based structures. These results may enable the design of graphene-based organic magnets with tailored properties for future magnetic or spintronic applications.

Unveiling multiferroic proximity effect in graphene

We demonstrate that electronic and magnetic properties of graphene can be tuned via proximity of multiferroic substrate. Our first-principles calculations performed both with and without spin–orbit coupling clearly show that by contacting graphene with bismuth ferrite BiFeO3 (BFO) film, the spin-dependent electronic structure of graphene is strongly impacted both by the magnetic order and by electric polarization in the underlying BFO. Based on extracted Hamiltonian parameters obtained from the graphene band structure, we propose a concept of six-resistance device based on exploring multiferroic proximity effect giving rise to significant proximity electro- (PER), magneto- (PMR), and multiferroic (PMER) resistance effects. This finding paves a way towards multiferroic control of magnetic properties in two dimensional materials.

Two-dimensional carbon nitride (2DCN) nanosheets: Tuning of novel electronic and magnetic properties by hydrogenation, atom substitution and defect engineering

By employing first-principles calculations within the framework of density functional theory, we investigated the structural, electronic, and magnetic properties of graphene and various two-dimensional carbon-nitride (2DNC) nanosheets. The different 2DCN gives rise to diverse electronic properties such as metals (C3N2), semimetals (C4N and C9N4), half-metals (C4N3), ferromagnetic-metals (C9N7), semiconductors (C2N, C3N, C3N4, C6N6, and C6N8), spin-glass semiconductors (C10N9 and C14N12), and insulators (C2N2). Furthermore, the effects of adsorption and substitution of hydrogen atoms as well as N-vacancy defects on the electronic and magnetic properties are systematically studied. The introduction of point defects, including N vacancies, interstitial H impurity into graphene and different 2DCN crystals, results in very different band structures. Defect engineering leads to the discovery of potentially exotic properties that make 2DCN interesting for future investigations and emerging technological applications with precisely tailored properties. These properties can be useful for applications in various fields such as catalysis, energy storage, nanoelectronic devices, spintronics, optoelectronics, and nanosensors.

First principles study on the functionalization of graphene with Fe catalyst for the detection of CO2: Effect of catalyst clustering

The surface functionalization of graphene plays an important role in the development of graphene-based sensors for gas detection and removal. Here, we report the effect of decoration of graphene with Fe catalyst, as either scattered adatoms (Feadatoms@G) or clustered (Fecluster@G) on the detection of CO2 gas molecule and its influence on the structural, adsorption, electronic and magnetic properties of graphene using the spin-polarized density functional theory (DFT). The results show that the adsorption of scattered Fe-adatoms and Fe4-cluster on graphene would break the degeneracy of spin-up and spin-down states, resulting in ferromagnetic adsorption-bed for the detection of CO2 molecules. The magnetic moment of Feadatoms@G remains the same for all concentration of CO2, while the magnetic moment of Fecluster@G decreases from 10.03 µB to 4 µB by increasing the concentration of CO2 from one to four molecules. It is found that the scattered Fe-adatoms on graphene have the higher tendency to adsorb more CO2 molecules than that of the cluster with the same number of Fe atoms, whereas Fe4-cluster on graphene detects CO2 molecules using magnetism. Our results have indeed a direct application to fabricate solid-state and magnetic-based gas sensors using graphene to detect CO2 gas molecules.

Electronic Structure and Magnetic Properties of Graphene/Ni3Mn/Ni(111) Trilayer

Experimental and theoretical studies of manganese deposition on graphene/Ni(111) show that a thin ferromagnetic Ni3Mn layer, which is protected by a graphene overlayer, is formed upon Mn intercalation. The electronic bands of graphene are affected by Ni3Mn interlayer formation through a slight reduction of n-type doping compared to graphene/Ni(111) and a suppression of the interface states characteristic of graphene/Ni(111). Our density functional theory-based theoretical analysis of interface geometric, electronic, and magnetic structure gives strong support to our interpretation of the experimental scanning tunneling microscopy, low energy electron diffraction, and photoemission results and shows that the magnetic properties of graphene on Ni(111) are strongly influenced by Ni3Mn formation.

Graphene and its derivatives for Nanoscale Semiconductor Memories-A Density Functional Theory based approach

Memory occupies large portion of semiconductor industry. A lot of researches are going about new memory materials.In this paper we explore electronic, optical and magnetic properties of graphene and graphene nanoribbons for semiconductor memory applications.Graphene is having high mobility, good scaling properties.Also it shows Ferromagnetic and anti ferromagnetic properties.Measurable Optical properties are appeared in literature. All these properties are tunable with band gap .These factors point outs that graphene is a suitable candidate for making memories of various categories such as flash,optical storage devices,magnetic RAM etc.The bandgap of the graphene is a considerable design problem when making electronic devices.But nanoribbons can solve this issue and can provide enough band gap suitable for memory devices.Short channel effects scattering,ambipolar conduction is another point that need attention

Tuning the electronic and magnetic properties of graphene/h-BN hetero nanoribbon: A first-principles investigation

Inspired by the successful synthesis of phase separated in-plane graphene/h-BN heterostructures, we have explored the design of one dimensional graphene/h-BN hetero nanoribbon (G/BNNR). Using first-principles density functional based approach, the electronic and magnetic properties of the hybrid nanoribbons with mono-hydrogenated edges have been investigated for different configurations with alternative composition of C-C and B-N units in a ribbon of fixed width. Our results suggest that the electronic as well as magnetic properties of the ribbons can be regulated by varying the number of C-C (or B-N) units present in the structure. Both the hetero nanoribbons, either with N or B terminated edges, undergo a semiconductor-to-semimetal-to-metal transition with the increase in the number of C-C units for a fixed ribbon width. The spin density distribution indicates significant localization of the magnetic moments at the edge carbon atoms, that gets manifested when the number of C-C units is greater than 2 for most of the structures.

Hydrogen adatom interaction on graphene: A first principles study

Interaction between two hydrogen adatoms on graphene was studied by first-principles calculations. We showed that there is an attraction between two H adatoms on graphene. However, the strength of interaction between two hydrogen adatoms and magnetic properties of graphene are strongly dependent on the residence of the two adatoms on the graphene sublattices. Hydrogen adatoms introduce lattice distortion and electron localization in graphene which mediate the attractive interaction between the two H adatoms.

Temperature-tuned ferromagnetism in hydrogenated multilayer graphene.

Improving the ferromagnetism properties of pure carbon-based materials is extremely important for their application in spintronics. Hydrogenation of graphene is an effective way to induce magnetic moment into graphene with the advantage of reversibility. However, little experimental work has been done to prove the effect of hydrogen on the magnetic properties of graphene so far, except for systems containing a large amount of oxygen or plasma-induced vacancy which complicated the magnetic origin. Here we report a facile electrochemical cathodic method to generate hydrogenated multilayer graphene or few-layer graphite using graphite powder as the raw material, and observed hydrogen-induced ferromagnetism in samples annealed at different temperatures. The observed results suggest that ferromagnetism of hydrogenated multilayer graphene can be tuned by high temperature treatment, which is attributed to a changeable relative amount of hydrogen atoms chemisorpted on two different sublattices during thermal treatment.

Reduced graphene oxide-germanium quantum dot nanocomposite: electronic, optical and magnetic properties

Graphene provides numerous possibilities for structural modification and functionalization of its carbon backbone. Localized magnetic moments can, as well, be induced in graphene by the formation of structural defects which include vacancies, edges, and adatoms. In this work, graphene was functionalized using germanium atoms, we report the effect of the Ge ad atoms on the structural, electrical, optical and magnetic properties of graphene. Reduced graphene oxide (rGO)-germanium quantum dot nanocomposites of high crystalline quality were synthesized by the microwave-assisted solvothermal reaction. Highly crystalline spherical shaped germanium quantum dots, of diameter ranging between 1.6–9.0 nm, are anchored on the basal planes of rGO. The nanocomposites exhibit high electrical conductivity with a sheet resistance of up to 16 Ω sq−1. The electrical conductivity is observed to increase with the increase in Ge content in the nanocomposites. High defect-induced magnetization is attained in the composites via germanium adatoms. The evolution of the magnetic moments in the nanocomposites and the coercivity showed marked dependence on the Ge quantum dots size and concentration. Quantum confinement effects is evidenced in the UV–vis absorbance spectra and photoluminescence emission spectra of the nanocomposites which show marked size-dependence. The composites manifest strong absorption in the UV region, strong luminescence in the near UV region, and a moderate luminescence in the visible region.

Potentiality of Density-Functional Theory in Analyzing the Devices Containing Graphene-Crystalline Solid Interfaces: A Review

Graphene-based devices have initiated unprecedented breakthrough in nanoelectronics. Due to its intrinsic ultrathin 2-D nature, the unique structural, mechanical, electronic, optical, and magnetic properties of graphene are found to be extremely dependent on its substrate material. For the synthesis of graphene with pretailored features or fabrication of graphene-based device with tunable functionality, understanding of the graphene interfaces with other materials are of pivotal importance. Density-functional theory (DFT) computations have been proved to be a powerful tool in investigating the interface properties of graphene-crystalline solids and to subsequently correlate the experimental findings with underlying mechanisms, as well as to explore their potential applications. This paper presents a comprehensive review on utility of DFT-based analysis for graphene interfaces/heterostructures with other crystalline solid materials including metals, semiconductors, and insulators. DFT computational efforts to choose the appropriate material for substrate catalyst, probe, and electrode in graphene synthesis/graphene-based nanodevice design have been critically reviewed including the investigation of different combination of complex interfaces as well as unconventional materials. Salient features, advantages, and constraints of the approach have also been summarized.

An easy approach to reveal the metallic nature of graphene by Breit–Wigner–Fano lineshapes using Raman spectroscopy

Electron–phonon coupling enhancement in metal‐doped single‐layer graphene has been investigated. Different metal adatoms were deposited on chemical vapor deposition (CVD) graphene and annealed at high temperature under vacuum. The interaction between these metals and graphene was studied by Raman spectroscopy. A significant variation in peak width has been observed as a function of annealing temperature. This broadening of the Raman features is understood as a consequence of the coupling of phonon with electron–phonon pairs, and its strength depends on the particular metal deposited. A typical softening and broadening of G peak in Raman spectrum is interpreted as Fano resonance, which is an interaction between a phonon and continuum. This asymmetry in G peak is further analyzed and fitted with Breit–Wigner–Fano lineshapes in terms of asymmetric factor (1/qBWF) for different metal‐doped samples as a function of annealing temperature. Hence we demonstrated an easy approach to study the transition from semi‐metallic to metallic nature of graphene. This study may extend the interest in electron–phonon coupling as it aims to manipulate the electronic and magnetic properties of graphene and other 2D systems. Copyright © 2017 John Wiley & Sons, Ltd.

Impurity effects in the magnetic oscillations on doped graphene with Zeeman splitting

The aim of this work is to describe the electronic and magnetic properties of graphene in a constant magnetic field, in the long wavelength approximation with random disorder. Taking into account the Zeeman effect, the electronic density of states for each spin is found and the de Haas van Alphen oscillations (dHvA) are found. The magnetic field is found to modulate the de Haas-van Alphen magnetization through the ratio of the Zeeman coupling and pseudospin-Landau coupling. In turn, the Pauli magnetization is studied showing that the Zeeman splitting and disorder introduces a dHvA oscillation period that depends on the magnetic field strength and generalizes the Onsager relation. In turn, a beat frequency appears that does not depend on B but increase linearly with the chemical potential. These results, which are different from those obtained in the standard nonrelativistic 2D electron gas, are attributed to its anomalous Landau level spectrum in graphene.

DFT study of the electronic structure and magnetism of defective graphene decorated with hydrogen-adatom

We studied the electronic structure and magnetism in graphene induced by vacancy-defect and hydrogen-pairing adatoms using density functional theory (DFT). The results indicated that the decorating of H-adatoms brought half-metallicity behaviors in graphene, which depended on the configurations with the different number of carbon atoms between the adsorption sites of H-adatoms. When the number is odd, the systems exhibited half-metallic. Furthermore, the PDOS results suggested that the electronic and magnetic properties of graphene were mainly controlled by the C atoms around the vacancy-defect. These results provide useful information to understand the modifying of the electronic structures in hydrogenated graphene.

Electronic and magnetic properties of graphene, silicene and germanene with varying vacancy concentration

The experimental realization of two-dimensional materials such as graphene, silicene and germanene has attracted incredible interest ranging from understanding their physical properties to device applications. During the fabrication and processing of these two-dimensional materials, structural defects such as vacancies may be produced. In this work we have systemically investigated the formation energies, electronic and magnetic properties of graphene, silicene and germanene with vacancies in the framework of spin polarized density functional theory. It is found that the magnetic moment of graphene and silicene with vacancies decreases with the increase in the concentration of vacancies. However, germanene remains non-magnetic irrespective of the vacancy concentration. Low-buckled silicene and germanene with vacancies may possess remarkable band gaps, in contrast to planar graphene with vacancies. With the formation of vacancies silicene and germanene demonstrate a transition from semimetal to semiconductor, while graphene turns to be metallic.