Asymmetric graphene model applied to graphite-like carbon-based ferromagnetism

TL;DR

This paper models room-temperature ferromagnetism in graphite-like carbon materials using asymmetric nano-graphene, showing that certain edge configurations favor high-spin states, explaining experimental observations.

Contribution

It introduces an asymmetric graphene model with specific edge modifications to explain ferromagnetism in graphite-like carbon, supported by molecular orbital and density functional theory calculations.

Findings

High-spin states are more stable in certain asymmetric graphene molecules.

Nitrogen substitution reverses the stability trend of spin states.

Results align with experimental ferromagnetism in carbon-based materials.

Abstract

Several experiments have recently found room-temperature ferromagnetism in graphite-like carbon based materials. This paper offers a model explaining such ferromagnetism by using an asymmetric nano-graphene. Our first typical model is C48H24 graphene molecule, which has three dihydrogenated (-CH2) zigzag edges. There are several multiple spin states competing for stable minimum energy in the same atomic topology. Both molecular orbital and density function theory methods indicate that the quartet state(S=3/2) is more stable than that of doublet (S=1/2), which means that larger saturation magnetization will be achieved. We also enhanced this molecule to an infinite length ribbon having many (-CH2) edges. Similar results were obtained where the highest spin state was more stable than lower spin state. In contrast, a nitrogen substituted (-NH) molecule C45N3H21 demonstrated opposite results. that is, the lowest spin state(S=1/2) is more stable than that of highest one(S=3/2), which arises from the slight change in atom position.