Control of impurity over entanglement in Heisenberg chain

The thermal entanglement in a three-qubit Heisenberg XXX spin chains with a impurity site is investigated under an external magnetic field. For a fixed ξ(ξ=2 or -2), we discussed the effect of the impurity parameter γ and the magnetic field B to the concurrence. The calculation results reveal that the impurity parameter γ and the magnetic field B can significantly effect the pair entanglement between the spin lattices with a different way on the case of anti-ferromagnetic (ξ=2) or ferromagnetic (ξ=-2).