Nitrogen doping opens possibilities for tailoring the electronic properties and band gap of graphene toward its applications, e.g., in spintronics and optoelectronics. One major obstacle is development of magnetically active N-doped graphene with spin-polarized conductive behavior. However, the effect of nitrogen on the magnetic properties of graphene has so far only been addressed theoretically, and triggering of magnetism through N-doping has not yet been proved experimentally, except for systems containing a high amount of oxygen and thus decreased conductivity. Here, we report the first example of ferromagnetic graphene achieved by controlled doping with graphitic, pyridinic, and chemisorbed nitrogen. The magnetic properties were found to depend strongly on both the nitrogen concentration and type of structural N-motifs generated in the host lattice. Graphenes doped below 5 at. % of nitrogen were nonmagnetic; however, once doped at 5.1 at. % of nitrogen, N-doped graphene exhibited transition to a ferromagnetic state at ∼69 K and displayed a saturation magnetization reaching 1.09 emu/g. Theoretical calculations were used to elucidate the effects of individual chemical forms of nitrogen on magnetic properties. Results showed that magnetic effects were triggered by graphitic nitrogen, whereas pyridinic and chemisorbed nitrogen contributed much less to the overall ferromagnetic ground state. Calculations further proved the existence of exchange coupling among the paramagnetic centers mediated by the conduction electrons.
Bibliographical noteFunding Information:
The authors acknowledge the support from the Ministry of Education, Youth and Sports of the Czech Republic under Project No. LO1305 and assistance provided by the Research Infrastructure NanoEnviCz supported by the Ministry of Education, Youth and Sports of the Czech Republic under Project No. LM2015073. P. B. acknowledges Palacký University institutional support. The authors thank Mrs. Ariana Fargašová and Dr. Juri Ugolotti (both from the Regional Centre of Advanced Technologies and Materials, Faculty of Science, Palacky University in Olomouc, Czech Republic) for Raman spectroscopy and TGA/EGA measurements, respectively. Z. S. and V. M. were supported by the Czech Science Foundation (GACR No. 15-09001S) and by specific university research (MSMT No. 20-SVV/2016). M. O. acknowledges funding from an ERC Consolidator grant (H2020) No. 683024. M.P. acknowledges a Tier 2 grant (MOE2013-T2-1-056; ARC 35/13) from the Ministry of Education, Singapore.
© 2017 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry