  The time evolution of the entanglement of a pair of two spin qubits is
investigated when the two qubits simultaneously couple to an environment of an
anisotropic Heisenberg XXZ spin chain. The entanglement of the two spin qubits
can be created and is a periodic function of the time if the magnetic field is
greater than a critical value. If the two spin qubits are in the Bell state,
the entanglement can be stored with relatively large value even when the
magnetic field is large.
