Magnetic properties of sulfur-doped graphene

Abstract

While studying magnetism of d-and f-electron systems has been consistently an active research area in physics, chemistry, and biology, there is an increasing interest in the novel magnetism of p-electron systems, especially in graphene and graphene-derived nanostructures. Bulk graphite is diamagnetic in nature, however, graphene is known to exhibit either a paramagnetic response or weak ferromagnetic ordering. Although many groups have attributed this magnetism in graphene to defects or unintentional magnetic impurities, there is a lack of compelling evidence to pinpoint its origin. To resolve this issue, we systematically studied the influence of entropically necessary intrinsic defects (e.g., vacancies, edges) and extrinsic dopants (e.g., S-dopants) on the magnetic properties of graphene. We found that the saturation magnetization of graphene decreased upon sulfur doping suggesting that S-dopants demagnetize vacancies and edges. Our density functional theory calculations provide evidence for: i) intrinsic defect demagnetization by the formation of covalent bonds between S-dopant and edges/vacancies concurring with the experimental results, and ii) a net magnetization from only zigzag edges, suggesting that the possible contradictory results on graphene magnetism in the literature could stem from different defect-types. Interestingly, we observed peculiar local maxima in the temperature dependent magnetizations that suggest the coexistence of different magnetic phases within the same graphene samples.

Modulating the electronic and magnetic properties of graphene

“…242 However, in a separate study, quenching of the previously developed local magnetic moment induced by vacancies was observed via S substitutional doping of graphene, which led to diamagnetic, weak ferromagnetic and antiferromagnetic states in graphene. 243 The S-G system maintains good electrocatalytic activity for the oxygen reduction reaction. 235 S-G prepared via acid exposure of graphene has been proven to be an excellent solid catalyst.…”

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

“…Based on the theoretical analysis presented below, it is speculated that upon further increase of sulfur concentration in the graphene lattice (up to ≈6.25 at%), the value of the saturation magnetization could further increase closely approaching ≈8 emu g −1 , a value reported for vertical graphenes, which are currently viewed as the magnetically strongest carbon‐based systems . Here, it should be stressed that indeed, sulfur atoms are embodied into the graphene lattice as a rise in the magnetization values is observed upon increase of sulfur doping; if sulfur atoms were simply added to the graphene sheets (i.e., as adatoms), they would saturate the dangling bonds and, hence, quench the magnetic moments induced by defects, resulting in a decrease in magnetization with potential alternation of the type of the magnetic state (from the ferromagnetic to paramagnetic or diamagnetic regime) . Such a manifestation is in line with theoretical predictions as discussed below.…”

“…Recently, it was experimentally shown that introduction of nitrogen in the graphene lattice decreases the magnetization values compared to those of defected graphene . Identical fashion in magnetization behavior was lately observed upon doping of graphene lattice with sulfur; weakening of the magnetic response and change in the type of magnetic ordering were explained in terms of saturation of dangling bonds by sulfur atoms and, hence, quenching of local magnetic moments induced by defects existing already in undoped graphenes …”

Sulfur and few-layer graphene interaction under thermal treatments

“…Also it was predicted that sulfur doping could open an energy band gap in graphene [8,9]. On the other hand, Zhu and coworkers [12] found that sulfur dopants quench magnetic ordering in graphene and in general sulfur changed the magnetic behavior of their samples. Other experimental studies in graphite-sulfur composites have found superconducting behavior below 35K [13].…”