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Unpaired electrons make graphene structure magnetic

Experimental study confirms 50-year-old prediction

by Mitch Jacoby
December 12, 2019 | A version of this story appeared in Volume 97, Issue 48

A colored scanning tunneling micrograph and a stick-and-ball model of an organic molecule.
Credit: EMPA
This bowtie-shaped graphene-like molecule (scanning tunneling micrograph, left) has unpaired electrons (blue and red regions, right), which render the molecule magnetic. C = gray; H = white.

After years of research, commercial graphene products have begun to emerge, but slowly. The pace might accelerate if in addition to having outstanding mechanical, electronic, and thermal properties, graphene were also magnetic, opening the door to spintronic applications. But pristine graphene is not magnetic. So researchers have tried, with limited success, functionalizing the material to make it magnetic. Now, researchers led by Roman Fasel of the Swiss Federal Laboratories for Materials Science and Technology and Xinliang Feng of the Technical University of Dresden have synthesized a graphene nanomaterial—a polycyclic aromatic hydrocarbon (PAH)—that is naturally magnetic as a result of its bonding structure (Nat. Nanotechnol. 2019, DOI: 10.1038/s41565-019-0577-9). Nearly 50 years ago, chemist Erich Clar predicted that chemical bonding in a hypothetical bowtie-shaped PAH with 11 fused rings would leave the molecule with unpaired electrons in its ground state, rendering it magnetic. Fasel, Feng, and coworkers have now made the compound via cyclization and ring-closing reactions of simpler starting materials. By using various microscopy and spectroscopy techniques, the researchers confirmed the molecule’s structure, composition, and room-temperature magnetism.


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