Hybrid super-lattices of graphene and hexagonal boron nitride: Ferro-magnetic semiconductor at room temperature

Rita Maji, Joydeep Bhattacharjee

Published 2018-09-21Version 1

Carbon(C) doped hexagonal boron nitride(hBN) has been reported to be ferromagnetic at room temperature. Substitution by C in hexagonal boron nitride(hBN) leads to formation of graphene islands, which can host finite magnetic moment if they cover different number of boron and nitrogen sites. From density functional theory and mean field Hubbard model, we present a microscopic understanding of interaction of magnetic graphene islands in hBN, which also explains the observed ferromagnetism in these systems. We find spatial separation of back transferred electrons of opposite spins on nitrogen(N) and boron(B) atoms due to Coulomb repulsion, to be responsible for the anti-ferromagnetic ordering of neighbouring magnetic islands of graphene in hBN. Such an hBN mediated AFM ordering can switch to ferromagnetic(FM), if interjected by unequal preference of spin at an intermediate site between the two magnetic islands, as possible due to presence of a third magnetic island between the two. Accordingly, we propose an inter-penetrating system of two ferri-magnetically ordered super-lattices of magnetic graphene islands in hBN, which can be a ferromagnetic semiconductor or a half-metal, and retain a net non-zero magnetic moment at room temperature.