C₈₀ Endofullerenes: Small magnetoelectric Bits

日時　2024年11月27日　（水）　14:00～15:30
場所　WPI-SKCM2研究棟（VBL）　2階　セミナー室（VBL204）
講師　Thomas Greber
(LDS group University of Zürich, Switzerland）

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].

[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.

問合せ先　奥田太一、出田真一郎（放射光研究所）