A research team at the U.S. Department of Energy’s (DOE) Argonne National Laboratory has placed armchair-edge graphene nanoribbons (AGNRs) on a gold surface. Since AGNRs become semiconductors at certain widths, this structure may offer advantages in speed, heat dissipation and power consumption in electronic devices and create new research paths in spintronics.

The goal was to use AGNRs to block magnetic interactions on a metal. The team focused on how the AGNRs affect these interactions in a molecule tightly adhered to gold using the phenomenon of Kondo resonance — a well-defined, temperature-dependent effect between a single magnetic atom or molecule and a metal’s free electrons. For this purpose, the team relied on a low-temperature scanning tunneling microscopy tool at Argonne’s Center for Nanoscale Materials.

The researchers produced two samples with a magnetic molecule known to have strong Kondo effects. One sample contained an AGNR layer and the other did not. The team mapped the tunneling voltage changes and the proportional Kondo temperatures across a nanoscale landscape on both magnetic molecules. The Kondo temperatures indirectly indicate the strength of the spin-electron interactions between the gold and the magnetic molecule.

The team was surprised to find that Instead of blocking the spin interactions between the magnetic molecule and the base metal, the AGNRs actually mediated the spin exchange, resulting in a Kondo effect nearly as strong as in the material lacking AGNRs.

“Initially we were searching for a different result. The project was designed to decouple both electronic and magnetic — spintronic — effects between the magnetic molecules and the gold crystal surface. We were surprised to find a robust spin coupling while the molecules are electronically decoupled,” said lead researcher of the study.

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