Vacancy induced magnetism in graphene and graphene ribbons

TL;DR

This paper investigates how vacancies and voids in graphene and graphene ribbons induce magnetic properties, revealing rules that connect defect structure to magnetic order and showing potential for magnetic applications.

Contribution

It introduces a mean field Hubbard model analysis linking defect structures to magnetic textures in graphene, based on Lieb theorem, and explores defect interactions and magnetic behavior in ribbons.

Findings

Magnetic textures depend on defect sublattice imbalance.

Maximum defect density exists in semiconducting ribbons beyond which magnetization vanishes.

Graphene with uncoupled local moments exhibits giant Zeeman splitting similar to diluted magnetic semiconductors.

Abstract

We address the electronic structure and magnetic properties of vacancies and voids both in graphene and graphene ribbons. Using a mean field Hubbard model, we study the appearance of magnetic textures associated to removing a single atom (vacancy) and multiple adjacent atoms (voids) as well as the magnetic interactions between them. A simple set of rules, based upon Lieb theorem, link the atomic structure and the spatial arrangement of the defects to the emerging magnetic order. The total spin $S$ of a given defect depends on its sublattice imbalance, but some defects with S=0 can still have local magnetic moments. The sublattice imbalance also determines whether the defects interact ferromagnetically or antiferromagnetically with one another and the range of these magnetic interactions is studied in some simple cases. We find that in semiconducting armchair ribbons and two-dimensional graphene without global sublattice imbalance there is maximum defect density above which local magnetization disappears. Interestingly, the electronic properties of semiconducting graphene ribbons with uncoupled local moments are very similar to those of diluted magnetic semiconductors, presenting giant Zeeman splitting.