Tuning antiferromagnetism of vacancies with magnetic fields in graphene nanoflakes

TL;DR

This paper investigates how magnetic fields can tune the antiferromagnetic interactions of vacancy-induced localized spins in graphene nanoflakes, revealing potential for in situ control of spin states relevant for spintronics.

Contribution

It introduces a tight-binding model including magnetic fields to predict tunable exchange coupling between localized vacancy states in graphene nanoflakes.

Findings

Magnetic field can switch exchange coupling from positive to zero.

Antiferromagnetic ground state with accessible Néel temperatures predicted.

Localized vacancy states exhibit controllable spin interactions.

Abstract

Graphene nanoflakes are interesting because electrons are naturally confined in these quasi-zero-dimensional structures, whereas confinement in bulk graphene would require a band gap. Vacancies inside the graphene lattice lead to localized states and the spins of such localized states may be used for spintronics. We perform a tight-binding description of a nanoflake with two vacancies and include a perpendicular magnetic field via a Peierls phase. The tunnel coupling strength and from it the exchange coupling between the localized states can be obtained from the energy splitting between numerically calculated bonding and antibonding energy levels. This allows us to estimate the exchange coupling J, which governs the dynamics of coupled spins. We predict the possibility of switching in situ from J>0 to J=0 by tuning the magnetic field. In the former case, the ground state will be antiferromagnetic with N\'eel temperatures accessible by experiment.