Magnetic structure at zigzag edges of graphene bilayer ribbons

TL;DR

This paper investigates the magnetic properties of zigzag edges in bilayer graphene ribbons, revealing edge ferromagnetism driven by flat band edge states and showing significant magnetization at small electronic repulsions.

Contribution

It demonstrates that bilayer graphene ribbons exhibit edge ferromagnetism due to flat edge-state bands, a novel insight into their magnetic structure.

Findings

Edge magnetization as large as 0.2 μB per site at small U

Ferromagnetic edges with antiferromagnetic coupling between opposite edges

Magnetic structure driven by edge state properties

Abstract

We study the edge magnetization of bilayer graphene ribbons with zigzag edges. The presence of flat edge-state bands at the Fermi energy of undoped bilayer, which gives rise to a strong peak in the density of states, makes bilayer ribbons magnetic at the edges even for very small on-site electronic repulsion. Working with the Hubbard model in the Hartree Fock approximation we show that the magnetic structure in bilayer ribbons with zigzag edges is ferromagnetic along the edge, involving sites of the two layers, and antiferromagnetic between opposite edges. It is also shown that this magnetic structure is a consequence of the nature of the edge states present in bilayer ribbons with zigzag edges. Analogously to the monolayer case, edge site magnetization as large as $m \approx0.2 \mu_{B}$ (per lattice site) even at small on-site Hubbard repulsion $U \approx 0.3 {eV}$ is realized in nanometer wide bilayer ribbons.