Hybrid superlattices of graphene and hexagonal boron nitride: A ferromagnetic semiconductor at room temperature

TL;DR

This paper provides a mechanistic understanding of ferromagnetism in graphene islands embedded in hBN, proposing a class of superlattices that can be ferromagnetic semiconductors or half-metals at room temperature.

Contribution

It introduces a first-principles and mean-field Hubbard model analysis of ferromagnetism in graphene-hBN superlattices, revealing a pathway to room-temperature ferromagnetic semiconductors.

Findings

Ferromagnetism in graphene islands within hBN is explained by super-exchange interactions.

Embedded graphene islands can form ferri-magnetic superlattices with net magnetic moments at room temperature.

Proposed superlattices can be engineered to be ferromagnetic semiconductors or half-metals.

Abstract

Carbon (C) doped hexagonal boron nitride (hBN) has been experimentally reported to be ferromagnetic at room temperature. Substitution by C in hBN has been also reported to form islands of graphene. In this work we derive a mechanistic understanding of ferromagnetism with graphene islands in hBN from first principles and mean-field Hubbard model. We find a general property, that in bipartite lattices where the sublattices differ in on-site energies, as in hBN, the ordering between local magnetic moments can be substantial and predominantly anti-ferromagnetic (AFM) if they are embedded in the same sublattice, unless dominated by Mott like inter-sublattice spin separation due to strong localization. The dominant AFM order is rooted at spin resolved spatial separation of lone pairs of nitrogen (N) and back transferred electrons on boron (B) due to Coulomb repulsion thus essentially implying a super-exchange pathway. Subsequently we propose a class of ferri-magnetically ordered inter-penetrating super-lattices of magnetic graphene islands in hBN, which can be chosen to be a ferromagnetic semiconductor or a half-metal, and retain a net non-zero magnetic moment at room temperature.