Electron spin resonance of single iron phthalocyanine molecules and role of their non-localized spins in magnetic interactions

NOVEMBER 11, 2021

Xue Zhang, Christoph Wolf, Yu Wang, Hervé Aubin, Tobias Bilgeri, Philip Willke, Andreas J. Heinrich & Taeyoung Choi
Nat. Chem.(2021)


Electron spin resonance technique have been a crucial tool to investigate chemical and electronic structure of materials with unpaired spins. In recent years, a newly developed ESR-STM has been a powerful tool to coherently drive individual atom spins on surfaces. We have extended this technique to investigate a broader class of matter - molecules and for the first time, we successfully drive a spin from individual FePC molecules and further find that the molecular ligand plays important role for spin-spin exchange interaction. This result may open up the door to directly image spin distribution of molecules and to utilize spin-spin interaction between molecules for molecule-based quantum technology.


Electron spin resonance (ESR) spectroscopy is a crucial tool, through spin labelling, in investigations of the chemical structure of materials and of the electronic structure of materials associated with unpaired spins. ESR spectra measured in molecular systems, however, are established on large ensembles of spins and usually require a complicated structural analysis. Recently, the combination of scanning tunnelling microscopy with ESR has proved to be a powerful tool to image and coherently control individual atomic spins on surfaces. Here we extend this technique to single coordination complexes—iron phthalocyanines (FePc)—and investigate the magnetic interactions between their molecular spin with either another molecular spin (in FePc–FePc dimers) or an atomic spin (in FePc–Ti pairs). We show that the molecular spin density of FePc is both localized at the central Fe atom and also distributed to the ligands (Pc), which yields a strongly molecular-geometry-dependent exchange coupling.