Long-range exchange interaction between magnetic impurities in graphene

TL;DR

This paper investigates how the magnetic exchange interaction between impurities in graphene varies with the impurity potential strength, revealing long-range and tunable magnetic couplings influenced by impurity levels near the Dirac points.

Contribution

It demonstrates that increasing the impurity potential extends the range of exchange interactions and causes a switch from antiferromagnetic to ferromagnetic coupling at specific distances.

Findings

Exchange coupling becomes long-range with higher potential U.

Coupling switches from antiferromagnetic to ferromagnetic when impurities are on opposite sublattices.

Resonant enhancement occurs at impurity levels crossing the Dirac point.

Abstract

The effective spin exchange coupling between impurities (adatoms) on graphene mediated by conduction electrons is studied as a function of the strength of the potential part of the on-site energy $U$ of the electron-adatom interaction. With increasing $U$, the exchange coupling becomes long-range, determined largely by the impurity levels with energies close to the Dirac points. When adatoms reside on opposite sublattices, their exchange coupling, normally antiferromagnetic, becomes ferromagnetic and resonantly enhanced at a specific distance where an impurity level crosses the Dirac point.