  The entanglement quantum properties of a spin-1/2 Ising-Heisenberg model on a
symmetrical diamond chain were analyzed. Due to the separable nature of the
Ising-type exchange interactions between neighboring Heisenberg dimers,
calculation of the entanglement can be performed exactly for each individual
dimer. Pairwise thermal entanglement was studied in terms of the isotropic
Ising-Heisenberg model, and analytical expressions for the concurrence (as a
measure of bipartite entanglement) were obtained. The effects of external
magnetic field $H$ and next-nearest neighbor interaction $J_m$ between nodal
Ising sites were considered. The ground-state structure and entanglement
properties of the system were studied in a wide range of the coupling constant
values. Various regimes with different values of the ground-state entanglement
were revealed, depending on the relation between competing interaction
strengths. Finally, some novel effects, such as the two-peak behavior of
concurrence versus temperature and coexistence of phases with different values
of magnetic entanglement were observed.
