Magnetic Nanostructured Graphene

Møller, Ulrik Svanborg

4. term

Nanotechnology, Master

2013

2013-07-10

81

Vi undersøger de elektroniske egenskaber i nanostruktureret grafen ved hjælp af en Hubbard-model i middelfelts-tilnærmelse, som medtager vekselvirkninger op til tredje-nærmeste naboer. Vi analyserer båndgab og magnetiske grundtilstande i tre typer strukturer: 0D grafenflager, 1D grafennanobånd og 2D triangulære antidot-gitre med hexagonale huller. Grafens gitter kan opdeles i to delgitre (A/B). Når der er ubalance mellem delgitrene, finder vi ferromagnetisme (spinnene peger samme vej). For balancerede delgitre identificerer vi en kritisk størrelse, over hvilken grundtilstanden bliver antiferromagnetisk (spinnene veksler). Den antiferromagnetiske grundtilstand øger båndgabet, hvilket kan give store båndgab og har en markant effekt på den optiske respons (hvordan materialet interagerer med lys). Til sidst undersøger vi stabiliteten af de antiferromagnetiske tilstande ved stigende temperatur og doping (tilsætning af urenheder). Strukturerne depolariserer, dvs. mister den magnetiske orden, omkring T ~ 1000 K og ved doping på ~1%.

We study the electronic properties of nanostructured graphene using a mean-field Hubbard model that includes interactions up to third-nearest neighbors. We examine band gaps and magnetic ground states in three types of structures: 0D graphene flakes, 1D graphene nanoribbons, and 2D triangular graphene antidot arrays with hexagonal holes. Graphene’s lattice can be divided into two sublattices (A/B). When there is a sublattice imbalance, we find ferromagnetism (spins align). For balanced sublattices, we identify a critical size above which the ground state becomes antiferromagnetic (spins alternate). The antiferromagnetic ground state increases the band gap, leading to large gaps and a strong effect on the optical response (how the material interacts with light). Finally, we assess the stability of these antiferromagnetic states under higher temperature and doping (adding impurities). The structures depolarize, i.e., lose magnetic order, around T ~ 1000 K and at doping of ~1%.

[This abstract was generated with the help of AI]

graphene ; nanostructured ; ribbon ; Hubbard ; mean-field ; tight binding ; antidot ; GAL ; GHAL ; flakes ; spin ; spin polarized ; magnetic ; ZGNR ; AGNR ; doping ; optical response ; optical conductivity ; ferromagnetic ; antiferromagnetic ; exact diagonalization ; nanoribbon ; hexagonal holes ; Lieb's theorem ; band gap ; sublattice imbalance ; critical size ; second quantization ; density of states ; projected density of states ; DOS ; PDOS ; simple scaling law ; zigzag ; armchair

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