Spin shuttle is a term coined for endofullerene molecules which encage and protect an atom or molecule with an open electron shell. Such molecules are candidates for single molecule magnets and have a great potential as building blocks in molecular spintronics. A single molecule magnet is a molecule that retains its magnetization direction for a long time, i.e. displays hysteresis. The first single molecule magnet spin shuttle was DySc₂N@C₈₀ (Westerström et al. Journal of the American Chemical Society 134, 9840 (2012)) (article).

Model of DySc₂N@C₈₀ (diameter 1.1 nanometer). The electron density of the Dy 4f⁹ shell in the j_z = ¹⁵/₂ ground state is indicated in red inside the yellow sphere (for enlargement click image). The non-isotropic shape of the open 4f shell is the source of the magnetic anisotropy and the long spin relaxation times of the Dy ion inside C₈₀. It couples to the ligand field of the central nitrogen atom (green) and the carbon cage. Picture copyright Ari P Seitsonen.