Contrasting interedge superexchange interactions of graphene nanoribbons embedded in h-BN and graphane

TL;DR

This study compares the electronic and magnetic properties of ultranarrow zigzag graphene nanoribbons embedded in hexagonal boron nitride and graphane, revealing how interface structures influence superexchange interactions and magnetic states.

Contribution

It provides a first-principles analysis of how different interface structures in ZGNRs embedded in BN and graphane affect their magnetic interactions and electronic properties.

Findings

ZGNRs/BN are mostly nonmagnetic, with weak half-semimetallic states at certain widths.

ZGNRs/graphane exhibit strong antiferromagnetic coupling for widths N >= 2.

Different interface symmetries lead to contrasting superexchange interactions.

Abstract

Based on first-principles density-functional theory calculations, we present a comparative study of the elec- tronic structures of ultranarrow zigzag graphene nanoribbons (ZGNRs) embedded in hexagonal boron nitride (BN) sheet and fully hydrogenated graphene (graphane) as a function of their width N (the number of zigzag C chains composing the ZGNRs). We find that ZGNRs/BN have the nonmagnetic ground state except at N = 5 and 6 with a weakly stabilized half-semimetallic state, whereas ZGNRs/graphane with N >= 2 exhibit a strong antiferromagnetic coupling between ferromagnetically ordered edge states on each edge. It is revealed that the disparate magnetic properties of the two classes of ZGNRs are attributed to the contrasting interedge superexchange interactions arising from different interface structures: i.e., the asymmetric interface structure of ZGNRs/BN gives a relatively short-range and weak superexchange interaction between the two inequivalent edge states, while the symmetric interface structure of ZGNRs/graphane gives a long-range, strong interedge superexchange interaction.