Antiferromagnetism in hexagonal graphene structures: Rings vs dots

TL;DR

This study uses the mean-field Hubbard model to compare antiferromagnetic properties of hexagonal graphene rings and dots, revealing edge shape and defect effects on magnetization.

Contribution

It demonstrates that graphene rings can exhibit stronger antiferromagnetic interactions than dots, influenced by edge configurations and hybridization of edge states.

Findings

Rings have larger antiferromagnetic interaction than dots.

Edge shape significantly affects magnetization, with zigzag edges maximizing it.

Armchair edges in narrow rings lead to higher magnetization and robustness against defects.

Abstract

The mean-field Hubbard model is used to investigate the formation of the antiferromagnetic phase in hexagonal graphene rings with inner zigzag edges. The outer edge of the ring was taken to be either zigzag or armchair, and we found that both types of structures can have a larger antiferromagnetic interaction as compared with hexagonal dots. This difference could be partially ascribed to the larger number of zigzag edges per unit area in rings than in dots. Furthermore, edge states localized on the inner ring edge are found to hybridize differently than the edge states of dots, which results in important differences in the magnetism of graphene rings and dots. The largest staggered magnetization is found when the outer edge has a zigzag shape. However, narrow rings with armchair outer edge are found to have larger staggered magnetization than zigzag hexagons. The edge defects are shown to have the least effect on magnetization when the outer ring edge is armchair shaped.