Edge-Driven Magnetic Ordering and Electronic Localization in Graphene Nanoflakes: A Model Hamiltonian and Exact Diagonalization Study
Keywords:
Graphene nanoflakes, edge magnetism, zigzag edges, Hubbard model, exact diagonalization, spin density, spin–spin correlation, molecular spintronics.Abstract
Graphene nanoflakes provide a finite-size platform for realising electronic localisation and magnetic ordering that are absent in pristine extended graphene. In this work, edge-driven magnetism in triangular, hexagonal, rectangular, and armchair graphene nanoflakes is investigated using a π-electron tight-binding/Hubbard model supported by exact diagonalisation. The study focuses on the influence of edge topology, sublattice imbalance, quantum confinement, and on-site Coulomb interaction on the low-energy electronic spectrum and magnetic ground state. The tight-binding analysis shows that zigzag-edged nanoflakes develop near-zero-energy frontier states localised along the boundary, whereas armchair flakes retain comparatively larger HOMO–LUMO (HOMO - Highest Occupied Molecular Orbital and LUMO - Lowest Unoccupied Molecular Orbital) gaps and weaker edge localisation. Inclusion of the Hubbard interaction reveals that triangular zigzag flakes possess finite total spin due to sublattice imbalance, consistent with the bipartite-lattice relation . Hexagonal zigzag flakes remain globally spin-compensated but exhibit local edge magnetic moments coupled antiferromagnetically between opposite sublattice regions. Spin-density and spin–spin correlation analyses confirm that magnetic ordering is concentrated mainly along zigzag edges and is governed by sublattice-dependent exchange coupling. The results establish nanographene as a geometry-controlled carbon-based magnetic system, where electronic localization and magnetic response can be tuned through nanoscale shape and edge engineering. These findings are relevant for molecular spintronics, quantum-confined graphene systems, and low-dimensional carbon nanomagnets.
DOI: https://doi.org/10.17762/ijisae.v12i23s.8269
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