Abstract
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.
Highlights
IntroductionChemical engineering and fabrication of single molecular spins is of vital importance in molecule-based quantum devices.1 To detect and control single molecular spins, there have been various approaches such as optical detection of diluted molecular spins 2-4, magnetic resonance force microscopy5, nitrogen-vacancy magnetometry6, and break junction-based molecular devices7-9
Conventional electron spin resonance (ESR) studies on chemical ensembles10,11 are a very useful tool to elucidate the chemical structures at the molecular level, but they rely on the order of
Previous ESR-scanning tunneling microscopy (STM) studies have focused on the spins of single transition metal adatoms12,14-16 rather than those of single molecules, besides early attempts on the organic molecule – α,γ-bisdiphenylene β-phenylallyl (BDPA) at room temperature and in ambient condition17
Summary
Chemical engineering and fabrication of single molecular spins is of vital importance in molecule-based quantum devices. To detect and control single molecular spins, there have been various approaches such as optical detection of diluted molecular spins 2-4, magnetic resonance force microscopy, nitrogen-vacancy magnetometry, and break junction-based molecular devices. To detect and control single molecular spins, there have been various approaches such as optical detection of diluted molecular spins 2-4, magnetic resonance force microscopy, nitrogen-vacancy magnetometry, and break junction-based molecular devices. To detect and control single molecular spins, there have been various approaches such as optical detection of diluted molecular spins 2-4, magnetic resonance force microscopy, nitrogen-vacancy magnetometry, and break junction-based molecular devices7-9 These systems typically require embedding the molecule in a solid-state host and lack the flexibility to locate and access individual spins, or harness intra- and intermolecular spin-spin interactions. DFT calculations, in good agreement with the experimental results, suggest that the spin density of the compound mainly located on the Fe centere spreads to the outer molecular ligands These findings highlight the role of non-localized spins in the transfer of magnetic interactions, which can be crucial for fabricating molecular devices
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