Ferromagnetism in graphene nanoribbons: split versus oxidative unzipped ribbons

TL;DR

This study compares the magnetic properties of two types of graphene nanoribbons, revealing distinct ferromagnetic behaviors and defect-related magnetism, with potential implications for spintronic applications.

Contribution

It provides a comparative analysis of potassium-split and oxidative unzipped graphene nanoribbons, highlighting their different magnetic properties and underlying defect-related mechanisms.

Findings

Room temperature ferromagnetism persists only in potassium-split ribbons.

GNRs exhibit negative exchange bias, while CCGNRs show positive exchange bias.

Defects in carbon are likely responsible for magnetic behavior.

Abstract

Two types of graphene nanoribbons: (a) potassium-split graphene nanoribbons (GNRs), and (b) oxidative unzipped and chemically converted graphene nanoribbons (CCGNRs) were investigated for their magnetic properties using the combination of static magnetization and electron spin resonance measurements. The two types of ribbons possess remarkably different magnetic properties. While the low temperature ferromagnet-like feature is observed in both types of ribbons, such room temperature feature persists only in potassium-split ribbons. The GNRs show negative exchange bias, but the CCGNRs exhibit a 'positive exchange bias'. Electron spin resonance measurements infer that the carbon related defects may responsible for the observed magnetic behaviour in both types of ribbons. Furthermore, proton hyperfine coupling strength has been obtained from hyperfine sublevel correlation experiments performed on the GNRs. Electron spin resonance provides no indications for the presence of potassium (cluster) related signals, emphasizing the intrinsic magnetic nature of the ribbons. Our combined experimental results may infer the coexistence of ferromagnetic clusters with anti-ferromagnetic regions leading to disordered magnetic phase. We discuss the origin of the observed contrast in the magnetic behaviours of these two types of ribbons.