  Magnetic hysteresis is a direct manifestation of non-equilibrium physics that
has to be understood if a system shall be used for information storage and
processing. The dilanthanide endofullerene Tb2ScN@C80 is shown to be a
single-molecule magnet with a remanence time in the order of 100 s at 400 mK.
Three different temperature dependent relaxation barriers are discerned. The
lowest 1 K barrier is assigned to intermolecular interaction. The 10 K barrier
to intramolecular exchange and dipolar coupling and the 50 K barrier to
molecular vibrations as it was observed for Dy2ScN@C80. The four orders of
magnitude difference in the prefactor between the Tb and the Dy compound in the
decay process across the 10 K barrier is assigned to the electron number in the
4f shells that evidences lack of Kramers protection in Tb3+. The sub-Kelvin
hysteresis follows changes in the magnetisation at adiabatic and non-adiabatic
level crossings of the four possible Tb2 ground state configurations as is
inferred from a zero temperature hysteresis model.
