  For an electron spin in coupling with an interacting spin chain via
hyperfine-type interaction, we investigate the dynamical evolutions of the
pairwise entanglement of the spin chain and a correlation function joined the
electron spin with a pair of chain spins in correspondence to the electron spin
coherence evolution. Both quantities manifest a periodic and a decaying
evolution. The entanglement of the spin bath is significant in distinguishing
the zero-coherence status exhibited in periodic and decoherence evolutions of
the electron spin. The periodical concurrence evolution of the spin bath
characterizes the whole system in a coherence-preserving phase, particularly
for the case that the associated periodic coherence evolution is predominated
by zero-value in the infinite chain-length limit, which was often regarded as
the realization of decoherence.
