  Quantum phase transition in dimerized antiferromagnetic Heisenberg spin chain
has been studied. A staircase structure in the variation of concurrence within
strongly coupled pairs with that of external magnetic field has been observed
indicating multiple critical points. Emergence of entanglement due to external
magnetic field or magnetic entanglement is observed for weakly coupled spin
pairs in the same dimer chain. Though closed dimerized isotropic XXX Heisenberg
chains with different dimer strengths were mainly explored, analogous studies
on open chains as well as closed anisotropic (XX interaction) chains with
tilted external magnetic field have also been studied.
