Graphene, a single two-dimensional sheet of carbon atoms with an arrangement mimicking the honeycomb hexagonal architecture, has captured immense interest of the scientific community since its isolation in 2004. Besides its extraordinarily high electrical conductivity and surface area, graphene shows a long spin lifetime and limited hyperfine interactions, which favors its potential exploitation in spintronic and biomedical applications, provided it can be made magnetic. However, pristine graphene is diamagnetic in nature due to solely sp2 hybridization. Thus, various attempts have been proposed to imprint magnetic features into graphene. The present review focuses on a systematic classification and physicochemical description of approaches leading to equip graphene with magnetic properties. These include introduction of point and line defects into graphene lattices, spatial confinement and edge engineering, doping of graphene lattice with foreign atoms, and sp3 functionalization. Each magnetism-imprinting strategy is discussed in detail including identification of roles of various internal and external parameters in the induced magnetic regimes, with assessment of their robustness. Moreover, emergence of magnetism in graphene analogues and related 2D materials such as transition metal dichalcogenides, metal halides, metal dinitrides, MXenes, hexagonal boron nitride, and other organic compounds is also reviewed. Since the magnetic features of graphene can be readily masked by the presence of magnetic residues from synthesis itself or sample handling, the issue of magnetic impurities and correct data interpretations is also addressed. Finally, current problems and challenges in magnetism of graphene and related 2D materials and future potential applications are also highlighted.

Emerging chemical strategies for imprinting magnetism in graphene and related 2D materials for spintronic and biomedical applications

Imprinting ferromagnetism to a graphene structure by substitution of carbon atoms with sulfur is reported. S-doped graphene (4.2 at%) shows strong ferromagnetic properties with saturation magnetization exceeding 5.5 emu g(-1) at 2 K, which is among the highest values reported for any sp-based system. The remarkable magnetic response is attributed to delocalization of electrons from sulfur injected into the graphene conduction band.

Sulfur Doping Induces Strong Ferromagnetic Ordering in Graphene: Effect of Concentration and Substitution Mechanism.

Graphene, an sp2 hybridized single sheet of carbon atoms organized in a honeycomb lattice, is a zero band gap semiconductor or semimetal. This emerging material has been the subject of recent intensive research due to the novelty of its structural, electronic, optical, mechanical, and magnetic properties. Due to these properties, graphene is a favorable material for the fabrication of electronic devices, transparent electrodes, spintronics devices, and a growing array of several other applications that explore the potential of this marvelous material. However, the lack of intrinsic band gap and nonmagnetic nature of graphene limit its practical applications in the widely expanding field of carbon-based devices. To take advantage of the hidden potential of this material, numerous techniques have been developed to tailor its electronic and magnetic properties. These methods include the mutual interaction between graphene layer and its substrate, doping with surface adatoms, substitutional doping, vacancy creation, and edges and strain manipulation. Herein, an overview of recently emerging innovative techniques adopted to tailor the electronic and magnetic properties of graphene is presented. The limitations, possible directions for future research and applications in diverse fields of these methods are also mentioned.

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Modulating the electronic and magnetic properties of graphene

To remove pollutants from industrial waste, magnetic separation by use of magnetic reduced graphene oxide (rGO) is a possible route, due to the high specific surface area of rGO. Reduced graphene oxide decorated with nickel, cobalt and cobalt ferrite nanoparticles was synthesized by means of modified coprecipitation methods. Nitrogen-doped reduced graphene was prepared by a thermal doping method. The resulting composites were characterized with scanning electron microscope, transmission electron microscope (TEM), powder X-ray diffraction (XRD), thermal analysis and Raman spectroscopy. Samples were magnetically characterized using vibrating sample magnetometer to determine the magnetic properties. All the prepared sampled were found to have weak ferromagnetic properties. The particle size distribution of the nanoparticles was determined using the TEM images and Image J software. The average particle size for the Co-rGO was 1.89 nm, 35.12 nm for Ni–rGO and 32.15 nm for CoFe–rGO. The Co–rGO was used as proof of principle to remove Cr(VI) ions from solution. The Co–rGO was recycled five times before it was deemed unusable.

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Synthesis, characterization and magnetic properties of Ni, Co and FeCo nanoparticles on reduced graphene oxide for removal of Cr(VI)

In recent years, heteroatoms-doped graphene, with its exceptional properties, has generated significant advances in many fields of modern nanoscience and nanotechnology. With the rapid progress in ...

A. Wadehra

Papers

Magnetic properties of sulfur-doped graphene