  Antiferromagnetic spin chains play an important role in condensed matter
physics and statistical mechanics. Recently XXX spin chain was discussed in
relation to the information theory. We consider here localizable entanglement,
introduced recently by F.Verstraete, M.Popp and J.I.Cirac. That is how much
entanglement can be localized on two spins on average by performing local
measurements on the other individual spins in a system of many interacting
spins. We consider the ground state in antiferromagnetic spin chains and study
localizable entanglement between two spins as a function of the distance. We
start with isotropic spin chain.
  Then we study effect of anisotropy and magnetic field. We conclude that
anisotropy increases localizable entanglement. We found an explicit dependence
of critical exponents in XXZ spin chain on magnetic field. We discovered that
the cases of high symmetry corresponds to high sensitivity of magnetic field.
We also calculated the concurrence before the measurement to illustrate that
the measurment raises the concurrence.
