HiSOR+WPI Seminar: Thomas Greber (LDS group University of Zürich, Switzerland), C80 Endofullerenes: Small magnetoelectric Bits
Fullerene carbon cages can encapsulate a small number of atoms. In a C80 shell, the endohedral units are cationic and have a nominal charge of +6. This charge is transferred to the cage, resulting in a stable molecule with a large HOMO-LUMO gap. As the carbon cage is not a perfect Faraday cage, the endohedral orientation can be sensed as an electric field outside the cage [1].
If the endohedral unit is paramagnetic, superparamagnetism is observed with 100 second blocking temperatures of several Kelvin [2]. Using X-ray absorption spectroscopy (XAS), the link between the electrostatic and magnetic endohedral orientation of Dy2ScN@C80 on Rh(111) was established [3]. It is also proposed that the endohedral units can realise coherently coupled bits [4].
In the case of CeTi@C80, the trivalent Ce3+ and Ti3+ ions sit front to front inside the C80 cage and the ligand field suggests single electrons without angular momentum in the 4f and 3d shells, respectively. It is shown that the orientation of the Ce-Ti axes can be changed by an electric field in a metal oxide semiconductor structure with a graphene gate [5].
References
[1] R. Stania et al. Electrostatic Interaction across a Single-Layer Carbon Shell, J. Phys. Chem. Lett. 9, 3586 (2018)
[2] R. Westerström et al. An operational definition of the 100 second blocking temperature TB100 for single molecule magnets, arXiv:1506.03657
[3] R. Westerström et al. Surface Aligned Magnetic Moments and Hysteresis of an Endohedral Single-Molecule Magnet on a Metal, Phys. Rev. Lett. 114, 087201 (2015)
[4] T. Greber, Quantum Tunneling of the Magnetization in Systems with Anisotropic 4f Ion Pairs: Rates from Low-Temperature Zero-Field Relaxation, ACS Omega 9, 37183 (2024)
[5] W.C. Lee, PhD thesis University of Zürich, in preparation.