Magnetization profile for impurities in graphene nanoribbons

Physical review. B, Condensed matter (Impact Factor: 3.77). 08/2011; 84. DOI: 10.1103/PhysRevB.84.195431
Source: arXiv

ABSTRACT 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 transition-metal 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
transition-metal doped GNRs are far more robust than those with moments arising
intrinsically due to edge geometry.

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    ABSTRACT: a b s t r a c t We performed ab initio density-functional calculations to investigate the structural, elec-tronic and magnetic properties of nanostructures comprising single-adatoms of Sc, Ti or V adsorbed on a hydrogen-passivated zigzag graphene nanoribbon (GNR). We also investi-gated the affinity of the resulting doped nanostructures for molecular hydrogen. In all cases, the most stable structures featured the adatom at positions near one of the edges of the GNR. However, whereas in the most stable structures of the systems Sc/GNR and V/GNR the adatom was located above a bay of the zigzag edge, Ti/GNR was found to be most stable when the adatom was at a first-row hole site. Adsorption at sites near one of the ribbon edges reduced drastically the average magnetic moment of the carbon atoms at that edge. On the other hand, the magnetic moments of the adatoms on the GNR, as the electronic character of the doped nanostructures, depended on the adsorption site and on the adatom species, but their absolute values were in all cases, except when Sc was at an edge bay site, greater than those of the corresponding free atoms. Our results showed that, of the three systems investigated in this paper, Ti/GNR (except when Ti is adsorbed at an edge bay site) and V/GNR appear to satisfy the criterion specified by the U. S. Department of Energy for efficient H 2 storage, as far as binding energy is concerned. We discussed in detail the differences be-tween the adsorption of H 2 on the system Ti/GNR and the adsorption of H 2 on Ti-adsorbed carbon nanotubes, which have been proposed as a high-capacity hydrogen storage media.
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    ABSTRACT: Magnetically-doped graphene systems are potential candidates for application in future spintronic devices. A key step is to understand the pairwise interactions between magnetic impurities embedded in graphene that are mediated by the graphene conduction electrons. A large number of studies have been undertaken to investigate the indirect exchange, or RKKY, interactions in graphene. Many of these studies report a decay rate faster than expected for a 2-dimensional material and the absence of the usual distance dependent oscillations. In this review we summarize the techniques used to calculate the interaction and present the key results obtained to date. The effects of more detailed parameterisations of the magnetic impurities and graphene host are considered, as are results obtained from ab initio calculations. Since the fast decay of the interaction presents an obstacle to spintronic applications, we focus in particular on the possibility of augmenting the interaction range by a number of methods including doping, spin precession and the application of strain.

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