Magnetism in graphene nano-islands

TL;DR

This paper investigates the magnetic properties of nanoscale graphene islands with different shapes, analyzing how their structure influences magnetic moments using theoretical models and density functional calculations.

Contribution

It provides a comparative analysis of magnetic behaviors in triangular and hexagonal graphene nano-islands, highlighting shape-dependent magnetic properties and their theoretical explanations.

Findings

Triangles exhibit finite total spin for all sizes.

Hexagons have zero total spin but develop local moments above 1.5 nm.

Magnetic properties are linked to shape, sublattice imbalance, and zero-energy states.

Abstract

We study the magnetic properties of nanometer-sized graphene structures with triangular and hexagonal shapes terminated by zig-zag edges. We discuss how the shape of the island, the imbalance in the number of atoms belonging to the two graphene sublattices, the existence of zero-energy states, and the total and local magnetic moment are intimately related. We consider electronic interactions both in a mean-field approximation of the one-orbital Hubbard model and with density functional calculations. Both descriptions yield values for the ground state total spin, $S$, consistent with Lieb's theorem for bipartite lattices. Triangles have a finite $S$ for all sizes whereas hexagons have S=0 and develop local moments above a critical size of $\approx 1.5$ nm.