PHYSICAL REVIEW B 87, 235440 (2013) Substrate-induced changes in the magnetic and electronic properties of hexagonal boron nitride Niharika Joshi and Prasenjit Ghosh Department of Chemistry and Physics, Indian Institute of Science Education and Research, Pune-411021, India (Received 16 April 2013; revised manuscript received 31 May 2013; published 28 June 2013) Using ab initio density functional theory we study the structure and electronic properties of hexagonal BN (h-BN) on Ni(111) and Co(0001) surfaces. Our calculations show that while dispersion interactions play an important role in stabilizing h-BN on the Ni(111) surface, on the Co(0001) surface it is primarily the covalent interactions. For h-BN on Ni(111) we show that semiempirical van der Waals correction proposed by Grimme to total energies obtained from density functional theory can correctly capture both the strong chemisorption minima closer to the surface and the weak physisorption minima further away from the surface. On both surfaces, the h-BN sheet becomes weakly ferrimagnetic. Additionally, on Ni(111) the h-BN sheet becomes half metallic and on Co(0001) it becomes metallic. DOI: 10.1103/PhysRevB.87.235440 PACS number(s): 81.05.ue, 73.22.Pr I. INTRODUCTION Ferromagnet-insulator interfaces have been an area of active research because of their potential applications as electronic devices in storage technology. 1 Both from the perspectives of fundamental physics and nanotechnology these interfaces play a key role in electron and spin transport. These properties are in turn governed by the electronic states near the Fermi energy. The electronic states of an interface may get modified due to the chemical interactions between the two components and sometimes are drastically different from those of the individual ones. For example, recently we have shown that nonmagnetic and semimetallic graphene, when grown on fcc (111) surfaces of Ni and Co and on hcp (0001) surface of Co, becomes ferrimagnetic with a slight opening up of the band gap at the K point of the Brillouin zone (BZ). 2,3 Therefore, it is desirable to have a detailed understanding of the electronic structure of these interfaces before using them for device applications. Two-dimensional hexagonal boron nitride (h-BN) [a sp 2 hybridized network of covalently bonded boron (B) and nitrogen (N) atoms in a honeycomb lattice] grown on Ni(111) surface is an ideal candidate to study these types of in- terfaces because h-BN forms an atomically sharp (1 × 1) superstructure which extends over large domains on this surface. Moreover, the almost perfect lattice matching between h-BN and Ni enables growth of stable, epitaxial overlayers without the formation of complex superstructures. h-BN is also interesting because though it is isoelectronic and isostructural with graphene, its properties are drastically different from graphene. For example, while graphene is a semimetal with a linear band dispersion at the K point of the BZ, h-BN is an insulator with a band gap of 5–6 eV. The opening of the band gap in h-BN arises from the difference in electronegativity of the B and N atoms. Over the past few years, there have been several studies, both experimental and density functional theory (DFT) based, of h-BN/Ni(111) interface. However, there is a lack of consensus regarding the type of interaction between h-BN and Ni (chemisorption or physisorption), and the electronic structure of the interface around the Fermi energy. For example, the first reports of h-BN/Ni(111) by Nagashima et al. 4 suggest very weak bonding between h-BN and the metal substrate. This was consistent with the generalized gradient approximation (GGA) based DFT calculations by Grad et al. 5 and Che and Chang, 6 where they found h-BN to be physisorbed on Ni(111) surface and insulating. Later Huda et al. showed that, while Perdew, Burke, and Ernzerhof (PBE) based GGA yields a physisorbed state, local density approximation (LDA) results in a chemisorbed one, 7 which is consistent with some recent experiments. 8,9 DFT based studies using the Wu-Cohen GGA exchange correlation functional by Laskowski et al. 10 showed an improved performance over PBE-GGA in the binding energy. Recent investigations of the formation of h-BN on the Ni(111) surface by Preobra- jenski et al. 11 using a combination of x-ray emission, angle resolved valence band photoemission, and x-ray absorption spectroscopies showed the presence of adsorption induced gap states of h-BN, making the supported h-BN sheet metallic. However, DFT calculations by Grad et al. 5 showed that the h-BN sheet remains insulating. Grad et al. also predicted a BN interface state which is about 2.0 eV above the Fermi energy. Spin and angle resolved inverse photoemission and spin-polarized secondary electron emission measurements by Zumbragel et al. 12 showed the presence of this state at 1.7 eV above the Fermi energy, which is exchange split by about 130 meV. In order to address the above-mentioned issues we present a detailed study of structure and electronic properties of the h-BN/Ni(111) surface. Based on the previous calculations, it is evident that, while PBE-GGA cannot correctly describe the interaction between h-BN and Ni(111), LDA gives reasonable results. 5,7 However, properties of the individual components are predicted more accurately by GGA than LDA. Hence it is desirable to have a correct description of the h-BN/Ni(111) surface within the PBE-GGA framework. We note that similar issues were also present for the graphene/Ni(111) interface, where it was shown that dispersion interactions play an important role. In order to investigate the role of dispersion interaction for h-BN-transition metal interfaces, in this work we have studied the interface using a PBE exchange correlation functional both with and without van der Waals correction. Additionally, we have also studied the h-BN/Co(0001) surface. Although for this case also there is an almost perfect lattice matching with h-BN, this interface is not well studied. To 235440-1 1098-0121/2013/87(23)/235440(8) ©2013 American Physical Society