  The ground entanglement and thermal entanglement in quantum mixed spin chains
consisting of two integer spins 1 and two half integer spins 1/2 arrayed as
${1/2}-{1/2}-1-1$ in a unit cell with antiferromagnetic nearest-neighbor
couplings $J_1$($J_2$) between the spins of equal (different) magnitudes, are
investigated by adopting the log-negativity. The ground entanglement transition
found here is closely related with the valence bond state transition, and the
thermal entanglement near the critical point is calculated and shown that two
distinct behaviors exist in the nearest neighbor same kind of spins and
different kind of spins, respectively. The potential application of our results
on the quantum information processing is also discussed.
