  Multiple relaxation times detected in the ac magnetic susceptibility of
several single-molecule magnets have been always assigned to extrinsic factors,
such as nonequivalent magnetic centers or effects of intermolecular
interactions in the crystal. By solving quantum relaxation equations, we prove
that the observed multiple relaxation times can be of intramolecular origin and
can show up even in single-ion metal complexes. For the latter a remarkably
good description of the coexistent two relaxation times is demonstrated on
several experimental examples. This proves the relevance of the intramolecular
mechanism of multiple relaxation times in such systems, which is even easier
justified in polynuclear magnetic complexes.
