Spin waves in zigzag graphene nanoribbons and the stability of edge ferromagnetism

TL;DR

This paper investigates the spin excitations and stability of edge ferromagnetism in zigzag graphene nanoribbons, revealing how doping and gate voltages influence spin wave lifetimes and magnetic order, impacting spintronic applications.

Contribution

It provides new insights into how doping and electrical gating affect edge ferromagnetism and spin wave dynamics in zigzag graphene nanoribbons.

Findings

Spin wave energies are dominated by antiferromagnetic edge correlations.

Gate voltages can induce a transition to longer spin wave lifetimes.

Doping destabilizes ferromagnetic edge alignments.

Abstract

We study the low energy spin excitations of zigzag graphene nanoribbons of varying width. We find their energy dispersion at small wave vector to be dominated by antiferromagnetic correlations between the ribbon's edges, in accrodance with previous calculations. We point out that spin wave lifetimes are very long due to the semi-conducting nature of the electrically neutral nanoribbons. However, application of very modest gate voltages cause a discontinuous transition to a regime of finite spin wave lifetime. By further increasing doping the ferromagnetic alignments along the edge become unstable against transverse spin fluctuations. This makes the experimental detection of ferromagnetism is this class of systems very delicate, and poses a difficult challenge to the possible uses of these nanoribbons as basis for spintronic devices.