Contributed talk

Tuning the spin interactions in all-organic diradicals through mechanical manipulation
Alessio Vegliante¹, Saleta Fernandez³, Manuel Vilas-Varela³, Ricardo Ortiz², Thomas Baum⁴, Niklas Friedrich¹, Francisco R. Lara¹, Andrea Aguirre¹, Carlos Garcia², Herre S. J. van der Zant⁴, Thomas Frederiksen², Diego Peña³ and Jose Ignacio Pascual¹

1 CIC nanoGUNE, San Sebastián (Spain)
2 Donostia International Physics Center, San Sebastián (Spain)
3 CiQUS-USC, Santiago de Compostela (Spain)
4 Delft University of Technology, Delft (The Netherlands)

Open-shell organic molecules have emerged as promising candidates for carbon-based spintronics. Purely organic molecules can exhibit magnetic properties because of the presence of one or more unpaired π-electrons. Organic diradicals, hosting two spin centers, are particularly interesting as model systems for investigating and manipulating magnetic interactions at the atomic scale.

In this work we study the magnetic state on a Au substrate of a diradical from the family of Chichibabin’s hydrocarbons by means of scanning tunneling microscopy (STM) and spectroscopy (STS). With the support of mean-field Hubbard calculations, we show that the spin-spin interaction is highly dependent on the precise geometrical conformation of the molecule. In particular, we find that a planarization of the molecular units stabilizes a singlet ground state (as we measure on the Au substrate), while less planar geometries tend to reduce the exchange coupling, resulting in non-interacting spins.

Following these findings, we demonstrate the possibility of tuning the spin-spin interaction in the diradical by means of mechanical manipulation, in two ways: i) approaching the STM tip towards the molecule to induce attractive/repulsive forces; ii) contacting one edge of the molecule to lift it from the substrate and recover a less planar conformation. These findings represent an important step towards the control of magnetic interactions within purely organic molecules.

Figure 1. (a) STM image and chemical structure of the Chichibabin’s diradical investigated in this work. (b) mechanical manipulation: dI/dV spectra taken at different tip heights, while lifting the molecule from the substrate.