Spin Transport and Magnetic Correlation Parameters for Graphene- like Nanocarbon Sheets Doped with Nitrogen Ashwini P. Alegaonkar, † Arvind Kumar, ‡ Sagar H. Patil, § Kashinath R. Patil, § Satish K. Pardeshi, † and Prashant S. Alegaonkar* ,‡ † Department of Chemistry, University of Pune, Pune 411 007, India ‡ Department of Applied Physics, Defence Institute of Advanced Technology, Pune 411 025, India § Centre for Materials Characterization, National Chemical Laboratory, Pashan Road, Pune 411 008, India * S Supporting Information ABSTRACT: Globally, graphene magnetism has captivated the attention of researchers in recent years. To obtain magnetic ordering, irregularities in the carbon network, like defects, adatoms, etc., are essential. Herein, we report on spin transport and magnetic correlations in graphene-like nanocarbon sheets (GNCs) that were doped with nitrogen by use of tetrakis- (dimethylamino)ethylene (TDAE). The spin transport measure- ments, performed by electron spin resonance technique, showed that both spin−spin and spin−lattice relaxation times are increased by nitrogen doping. The magnetic correlations, measured on a vibrating sample magnetometer, showed that ordering parameters are reduced for nitrogen-loaded GNCs. Chemical analysis, carried out via electron spectroscopy, revealed that nitrogen atoms exchange couples electron-to-hole with the carbon network. Analysis of I−V measurements showed that higher-order resistance is appreciably decreased for nitrogen-doped GNCs. The observed decrease is due to an increase in nonbonding states having small local density. After doping, states in this region may be localized π spin populated around the doped region. By and large, the approximately 20% magnetization that exists in GNCs is found to be reduced to 5% by introduction of nitrogen. 1. INTRODUCTION Magnetic materials are omnipresent components in today’s technology. Currently used metal magnets involved partially filled d- or f-band atoms. Pristine carbon is strongly diamagnetic, consisting of s and p electrons. However, in recent years, reports on the existence of ferromagnetic, antiferromagnetic, and paramagnetic ordering in carbon have become the focus of several investigations. The issue of carbon magnetism is controversial, intriguing, and originates due to size reduction of the system. A large number of experimental attempts have been made to demonstrate allotropes of carbon such as fullerenes, 1 highly ordered pyrolytic graphite, 2 carbon nanofoams, 3 and nanodiamonds 4 as magnetic materials. Graphene is not an exception. 5,6 The magnetic moments, in graphene, emerge due to zigzag edge states, 7 topological disorders, 2 unsaturated dangling bonds, 8 mixed sp 2 /sp 3 interconnected phases, 5 etc. Moreover, multishaped graphene fragments such as triangular, hexagonal nanoislands, 9 ribbons, 10 nanoflakes, 11 and fractal carbon 12 have shown high-spin ground states and behaved as artificial ferromagnetic atoms. To provide atomic-level understanding of the observed magnetism in carbon, numerous theoretical studies have been per- formed. 13−15 The studies showed that isolated vacancies and chemisorption of foreign atoms near vacancies could induce strong local magnetic moments. 16 The atomic origin of magnetic moments has three principal sources: (i) the spin with which electron are endowed, (ii) orbital angular momentum of electron about the nucleus, and (iii) the change in orbital momentum induced by external perturbations. The first two factors give spin−spin and spin−orbit (SO) interactions, and the third measures the strength of spin− orbit coupling. In graphene, SO interaction couples π and σ bands. The principal parameter governing usability of graphene in magnetic applications is spin−lattice relaxation time, T sl . The relaxation of spin coupled to its lattice depends on broken inversion symmetry 17 and the presence of heterostructure 18 in the two-dimensional graphene superlattice. The Elliott−Yafet mechanism 19 expalins the former case, and the latter is based on Dyakonov−Perel (DyP) theory. 20 The focus of the present invesitgation is to analyze spin transport and magnetic corelation paramters obtained for graphene-like nanocarbon sheets (GNCs) doped with nitrogen. Received: July 22, 2013 Revised: November 27, 2013 Published: December 2, 2013 Article pubs.acs.org/JPCC © 2013 American Chemical Society 27105 dx.doi.org/10.1021/jp407262w | J. Phys. Chem. C 2013, 117, 27105−27113