On-surface Synthesis of a Ferromagnetic Molecular Spin Trimer

TL;DR

This paper reports the synthesis and characterization of a complex triangulene-based nanographene with three unpaired electrons, demonstrating ferromagnetic coupling and a high-spin ground state suitable for spintronic applications.

Contribution

It introduces a novel N-doped triangulene nanostructure with three radical units that couple ferromagnetically, confirmed by experimental and theoretical analysis.

Findings

Successful synthesis of TTAT molecule on Au(111) surface

Detection of multi-radical coupling and high-spin state via STM and spectroscopy

Theoretical calculations confirm ferromagnetic coupling and S=3/2 ground state

Abstract

Triangulenes are prototypical examples of open-shell nanographenes. Their magnetic properties, arising from the presence of unpaired $\pi$ electrons, can be extensively tuned by modifying their size and shape or by introducing heteroatoms. Different triangulene derivatives have been designed and synthesized in recent years, thanks to the development of on-surface synthesis strategies. Triangulene-based nanostructures with polyradical character, hosting several interacting spin units, can be challenging to fabricate but are particularly interesting for potential applications in carbon-based spintronics. Here, we combine pristine and N-doped triangulenes into a more complex nanographene, \textbf{TTAT}, predicted to possess three unpaired $\pi$ electrons delocalized along the zigzag periphery. We generate the molecule on an Au(111) surface and detect direct fingerprints of multi-radical coupling and high-spin state using scanning tunneling microscopy and spectroscopy. With the support of theoretical calculations, we show that its three radical units are localized at distinct parts of the molecule and couple via symmetric ferromagnetic interactions, which result in a $S=3/2$ ground state, thus demonstrating the realization of a molecular ferromagnetic Heisenberg-like spin trimer