  We present a study of the entanglement properties of the F-AF zig-zag
Heisenberg chain done by means of the Density Matrix Renormalization Group
method. In particular, we have selected the concurrence as measure of
entanglement and checked its capability to signal the presence of quantum phase
transitions within the previously found ergodicity phase diagram [E. Plekhanov,
A. Avella, and F. Mancini, Phys. Rev. B \textbf{74}, 115120 (2006)]. By
analyzing the behavior of the concurrence, we have been able not only to
determine the position of the transition lines within the phase diagram of the
system, but also to identify a well defined region in the parameter space of
the model that shows a complex spin ordering indicating the presence of a new
phase of the system.
