Doping with Graphitic Nitrogen Triggers Ferromagnetism in Graphene

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Nitrogen doping is crucial for tuning graphene's electronic properties and band gap for spintronics and optoelectronics.
• A key challenge is creating magnetically active nitrogen-doped graphene with spin-polarized conductivity.
• Previous studies primarily relied on theoretical insights, with experimental evidence for N-doping-induced magnetism lacking, except in oxygen-rich, less conductive graphene.

Purpose of the Study:

• To experimentally demonstrate ferromagnetic graphene via controlled nitrogen doping.
• To investigate the influence of nitrogen concentration and structural motifs on magnetic properties.
• To elucidate the role of different nitrogen configurations in inducing magnetism.

Main Methods:

• Controlled doping of graphene with graphitic, pyridinic, and chemisorbed nitrogen.
• Characterization of magnetic properties, including ferromagnetic transition temperature and saturation magnetization.
• Theoretical calculations to analyze the impact of individual nitrogen chemical states on magnetism.

Main Results:

• Ferromagnetic graphene was successfully synthesized through controlled nitrogen doping.
• Magnetic properties were found to be highly dependent on nitrogen concentration and type of N-motifs.
• Nitrogen-doped graphene exhibited ferromagnetism at ~69 K with a saturation magnetization of 1.09 emu/g at 5.1 at. % nitrogen doping, while lower concentrations remained nonmagnetic.

Conclusions:

• This study presents the first experimental evidence of ferromagnetism in nitrogen-doped graphene.
• Graphitic nitrogen was identified as the primary driver of magnetism, with pyridinic and chemisorbed nitrogen contributing less.
• Theoretical calculations confirmed the role of graphitic nitrogen and revealed exchange coupling mediated by conduction electrons.