Diluted Graphene Antiferromagnet

TL;DR

This paper investigates RKKY interactions in graphene, revealing sublattice-dependent magnetic couplings, potential for magnetic ordering at low temperatures, and differences in interaction range between doped and undoped graphene.

Contribution

It provides a detailed analysis of magnetic interactions in graphene, highlighting sublattice effects and the impact of doping on interaction range and magnetic ordering.

Findings

Same-sublattice moments are ferromagnetically coupled.

Opposite-sublattice moments are antiferromagnetically coupled.

Doped graphene shows longer-range interactions than undoped.

Abstract

We study RKKY interactions between local magnetic moments for both doped and undoped graphene. We find in both cases that the interactions are primarily ferromagnetic for moments on the same sublattice, and antiferromagnetic for moments on opposite sublattices. This suggests that at sufficiently low temperatures dilute magnetic moments embedded in graphene can order into a state analogous to that of a dilute antiferromagnet. We find that in the undoped case one expects no net magnetic moment, and demonstrate numerically that this effect generalizes to ribbons where the magnetic response is strongest at the edge, suggesting the possibility of an unusual spin-transfer device. For doped graphene we find that moments at definite lattice sites interact over longer distances than those placed in interstitial sites of the lattice ($1/R^2$ vs. $1/R^3$) because the former support a Kohn anomaly that is suppressed in the latter due to the absence of backscattering.