  A quantum Heisenberg model with anisotropic coupling and all-to-all
interaction has been analyzed using the Bose-Einstein statistics. In
Ref.\cite{jsp} the existence of a classical energy disconnection border (EDB)
in the same kind of models has been demonstrated. We address here the problem
to find quantum signatures of the EDB. An independent definition of a quantum
disconnection border, motivated by considerations strictly valid in the quantum
regime is given. We also discuss the dynamical relevance of the quantum border
with respect to quantum magnetic reversal. Contrary to the classical case the
magnetization can flip even below the EDB through Macroscopic Quantum
Tunneling. We evaluate the time scale for magnetic reversal from statistical
and spectral properties, for a small number of particles and in the
semiclassical limit.
